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The Development of Thermal and Mechanical Property Tests for Mass Concrete

Permanent Link: http://ufdc.ufl.edu/UFE0021506/00001

Material Information

Title: The Development of Thermal and Mechanical Property Tests for Mass Concrete
Physical Description: 1 online resource (141 p.)
Language: english
Creator: Smith, Samuel J
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2007

Subjects

Subjects / Keywords: age, cement, concrete, early, flexure, heat, mass, specific, tension, thermal
Civil and Coastal Engineering -- Dissertations, Academic -- UF
Genre: Civil Engineering thesis, M.E.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Our study was aimed at contributing to the development of design parameters for mass concrete. It consisted of the assessment, procedural development, and testing for mechanical and thermal properties that are relevant to the cracking of mass concrete at early ages. With this assessment, it was chosen to develop the methodology behind testing for the elastic modulus, modulus of rupture, tensile strain capacity, and specific heat. In addition to concluding on the tests? viability, another objective was to evaluate these properties of concrete at a young age. The flexural test that was developed for early age concrete utilized third-point loading with surface mounted strain gages. The tensile strength and elastic modulus in tension and compression increased, and the tensile strain capacity decreased from 1 to 3 day tests. The elastic modulus of the compression region in the beam compared well to the estimated elastic modulus from the compressive strength using the equation indicated in ACI 8.5.1-2002, and the measured elastic modulus from compression cylinders. The tensile elastic moduli were generally lower than the elastic moduli in compression and is thought to be due to micro-cracking within the tension region at an early stage in the loading process. The observed difference between the measured strains in the tensile zone versus the compressive zone warrants further investigation into this area. The specific heat of early age concrete and its components were measured with the use of an insulated dewar flask. The lime rock, cement paste, and concrete were adequately measured using the 11 value moving average analysis. The concrete and cement paste specific heat increased with age, and is thought to be due to the diffusion of excess water into the pore structure where the cement has previously undergone hydration. While the lime rock worked well for the insulated flask test, higher variability was obtained for the sand samples due to it requiring less mass and a longer duration of equilibrium time.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Samuel J Smith.
Thesis: Thesis (M.E.)--University of Florida, 2007.
Local: Adviser: Birgisson, Bjorn.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2007
System ID: UFE0021506:00001

Permanent Link: http://ufdc.ufl.edu/UFE0021506/00001

Material Information

Title: The Development of Thermal and Mechanical Property Tests for Mass Concrete
Physical Description: 1 online resource (141 p.)
Language: english
Creator: Smith, Samuel J
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2007

Subjects

Subjects / Keywords: age, cement, concrete, early, flexure, heat, mass, specific, tension, thermal
Civil and Coastal Engineering -- Dissertations, Academic -- UF
Genre: Civil Engineering thesis, M.E.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Our study was aimed at contributing to the development of design parameters for mass concrete. It consisted of the assessment, procedural development, and testing for mechanical and thermal properties that are relevant to the cracking of mass concrete at early ages. With this assessment, it was chosen to develop the methodology behind testing for the elastic modulus, modulus of rupture, tensile strain capacity, and specific heat. In addition to concluding on the tests? viability, another objective was to evaluate these properties of concrete at a young age. The flexural test that was developed for early age concrete utilized third-point loading with surface mounted strain gages. The tensile strength and elastic modulus in tension and compression increased, and the tensile strain capacity decreased from 1 to 3 day tests. The elastic modulus of the compression region in the beam compared well to the estimated elastic modulus from the compressive strength using the equation indicated in ACI 8.5.1-2002, and the measured elastic modulus from compression cylinders. The tensile elastic moduli were generally lower than the elastic moduli in compression and is thought to be due to micro-cracking within the tension region at an early stage in the loading process. The observed difference between the measured strains in the tensile zone versus the compressive zone warrants further investigation into this area. The specific heat of early age concrete and its components were measured with the use of an insulated dewar flask. The lime rock, cement paste, and concrete were adequately measured using the 11 value moving average analysis. The concrete and cement paste specific heat increased with age, and is thought to be due to the diffusion of excess water into the pore structure where the cement has previously undergone hydration. While the lime rock worked well for the insulated flask test, higher variability was obtained for the sand samples due to it requiring less mass and a longer duration of equilibrium time.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Samuel J Smith.
Thesis: Thesis (M.E.)--University of Florida, 2007.
Local: Adviser: Birgisson, Bjorn.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2007
System ID: UFE0021506:00001


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8a51ad9124bb67acd92a75b8d4e0e2ff
60d2117c77e001c4925c0aed157a2ff1d175d4ec







THE DEVELOPMENT OF THERMAL AND MECHANICAL PROPERTY TESTS FOR
MASS CONCRETE




















By

SAMUEL J. SMITH


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF ENGINEERING

UNIVERSITY OF FLORIDA

2007





































O 2007 Samuel J. Smith









ACKNOWLEDGMENTS

Thank you Dr. Birgisson, Dr. Tia, Dr. Lybas, George Lopp, Chuck Broward, Chris

Ferrarro, Charles Ishee, Colin Swaysland, Nabil Hossiney, and all of my peers. Your help and

support is greatly appreciated.












TABLE OF CONTENTS


page

ACKNOWLEDGMENT S .............. ...............3.....


LI ST OF T ABLE S ............ ....._._. ...............7.....


LIST OF FIGURES .............. ...............8.....


AB S TRAC T ............._. .......... ..............._ 1 1..


CHAPTER


1 INTRODUCTION ................. ...............13......... .....


1.1 Problem Description............... ..............1
1.2 Fully Insulated Case ................. ...............14......... .....
1.3 Non-Insul ated Case ..........._..._ ...............16.......__......
1.4 Tests Developed ................. ...............17...............
1.4.1 Specific Heat ....._._ ................ ........_._ .........1
1.4.2 Flexural Test ....._._ ................. ........_._ .........1
1.5 Main Obj ectives of Study ................. ...............20.............
1.6 Scope of Work............... ...............20.


2 SURVEY OF SPECIFICATIONS .............. ...............28....


2.1 Introduction ....__. ................. .......__. ..........2
2.2 State Specifications .............. ...............28....
2.3 Government Agencies ........._._.... ...............3.. 1....__.. ...
2.3.1 U. S. Army Corps of Engineers .........__. ............ .....__. ..........3
2.3.2 U. S. Bureau of Reclamation ........._.__. ......... ...._... ...........3


3 LITERATURE REVIEW .............. ...............35....


3.1 Overview of Issues with Mass Concrete ........._._... .......... ......__...........3
3.2 Heats of Hydration .............. .... ......_ ... ... ...............36....
3.2.1 Temperature Prediction in Mass Concrete ................. ....__.. ................3 7
3.2.2 Low Heat Cements ................. ...............40........ .....
3.2.3 M ineral Ad mixtures ................ ...............41...
3.2.4 Other Methods to Lessen Heat ................. ...............42...............
3.3 Cracking ................. .... ......... .. .. ........... ........ ..... .......4
3.4 Mechanical Effects of Temperature and Relative Humidity Gradients ................... .....44
3.4.1 Internal Restraints .............. ...............45....
3.4.2 External Restraints ............... ...............46...
3.4.3 Temperature-Related Restraint .............. ...............46....
3.4.4 Relative Humidity-Related Restraint ................. ............. ......... .......49
3.4.4.1 Autogenous shrinkage .............. ...............50....












3.4.4.2 Drying shrinkage .............. ...............50....
3.4.4.3 Combinational effects ................... .... .......... ............. ............5
3.5 Chemical Effects of Extreme Temperature and Relative Humidity ................... ..........5 1
3.5.1 Immediate Effects .............. ...............52....
3.5.2 Long Term Effects .................... ....... ..........5
3.6 Measuring Mechanical Properties of Mass Concrete ................. .........................56
3.6.1 Tensile Strength ............... ...............58....
3.6.1.1 Direct tensile tests ................. ...............58................
3.6.1.2 Indirect tensile tests .............. ......... .............6
3.6.1.3 Hydro-static force induced tension tests ................. ............. .......63
3.6.1.4 Flexural test .............. ...............64....
3.6.2 Tensile Strain and Elasticity............... ...............6
3.6.3 Creep ......... ... ...............65....
3.7 Measuring Thermal Properties ................. ...............66................
3.7.1 Coefficient of Thermal Expansion ................. ...............66........... ...
3.7.2 Specific Heat ................ ...............67........... ....
3.7.3 Thermal Diffusivity............... ....... ..............6
3.7.4 Heat Production and Heat Production Rate .............. ...............68....
3.8 Summ ary .............. ...............69....


4 FLEXURAL TEST FOR EARLY AGE CONCRETE .............. ...............83....


4.1 Background .............. ... ...............83..
4.1.1 Early-Age Concrete ............ ...... .___ ...............83.....
4. 1.2 Third-Point Loading Scheme ......_.._._ .... ...._. .......__..........8
4.1.3 Compression Test for Elastic Modulus ..........._..__....._.. ......._.... .....84
4.2 Flexural Test Materials .............. ...............84....
4.2.1 Instrumentation .............. ...............84....
4.2.2 Sample Accessories ................. ...............85........... ....
4.2.3 Preparation Accessories .............. ...............85....
4.3 Flexural Test Procedure .............. ...............85....
4.3.1 Casting ............ .... ... ...............85
4.3.2 Sample Preparation and Storage .............. ...............86....
4.3.3 Testing ............ ...............86.....
4.3.4 Data Analysis .............. ...............86....
4.4 Results and Discussion............... ...............8
4.5 Summary and Conclusions............... ..............9


5 SPECIFIC HEAT FOR EARLY AGE CONCRETE AND ITS COMPONENTS ................97


5.1 Background .............. ...............97....
5.2 Insulated Flask Test............... ...............99..
5.2.1 Calorimeter Accessories............... ..............9
5.2.2 Data Instrumentation ............ ...... ...............100..
5.2.3 Cast Procedure ................ ...............100...
5.2.4 Test Procedure Calibration .............. ...............100....
5.2.5 Test Procedure With Material .............. ...............102....












5.2.6 Analysis 103
5.3 Transient Test............... ...............105.
5.3.1 Calorimeter Accessories. ......___ ..... .___ .....___ ..........10
5.3.2 Data Instrumentation ............ ...... ..__ ...............105..
5.3.3 Cast Procedure .............. .. ...............106...
5.3.4 Test Procedure Calibration............... ..............10
5.3.5 Analysis Calibration............... ..............10
5.3.6 Test Procedure With Material .............. ...............109....
5.3.7 Analysis With Material ............ .....___ ...............110.
5.4 Results and Discussion. ................ ...... ..._ .. ...............111.
5.4.1 Calorimeter Development and Sensitivity ............__.....___ ................111
5.4.2 Transient Test Complications ............ .......... ........_ ...........14
5.4.3 Mix Materials and Parameters ................. ...............114.......... ...
5.4.4 Concrete Specimens ................. ...............115...............
5.4.5 Paste Specimens ................. ...............117...............
5.4.6 Rock S ampl es ................. ...............117...............
5.4.7 Sand Samples ................. ...............118...............
5.5 Summary and Conclusions ................. ...............118......... .....


6 SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS .............. ....................13


6.1 Summary and Conclusions............... ..............13
6.1.1 Flexural Test. ........_................. ...............134.....
6. 1.2 Specific Heat Test ..............._ ............ ...............134...
6.2 Recommendations for Further Research ........ ................. ............... 135....
6.2.1 Characterization of Maturity ................. ...............135...............
6.2.2 Flexural Test ................. ...............135................
6.2.3 Specific Heat Test ................ ...............135...............


LIST OF REFERENCES ................. ...............137...............


BIOGRAPHICAL SKETCH ................. ...............141......... ......











LIST OF TABLES


Table page

2-1 Limiting conditions, indicated in mass concrete specifications taken from various
D O T's. ............. ...............33.....

2-2 Required amounts of mineral admixtures, indicated in mass concrete specifications
taken from various DOT's. ............. ...............34.....

3-1 Contribution of cement compounds to overall cement hydration ................. .................7 1

3-2 Properties of typical course aggregates ................. ...............72...............

3-3 Estimation of tensile strain capacity. ................ ...................... ..................72

4-1 Material weights used. ............. ...............91.....

4-2 Mix proportions used, according to PCA recommendations. ................... ...............9

4-3 Mechanical properties for three day aged cylinders. ............. ...............91.....

4-4 Mechanical properties for the beam ................. ...............91...............

4-5 Standard deviation for various tests and ages. ............. ...............92.....

5-1 Equilibrium times for the flask test and transient test ......... ................. ...............120

5-2 Specific heat and statistical results for transient test .............. ...............121....

5-3 Material weights used for concrete mix ................. ...............121........... ..

5-4 Specific heat values for the insulated flask test for concrete. ................... ...............12

5-5 Averages and standard deviation results for the insulated flask test for concrete. ..........122

5-6 Specific heat values for the insulated flask test for cement paste ................. ................122

5-7 Averages and standard deviation results for the insulated flask test for cement paste....123

5-8 Results for the insulated flask test for lime rock. ......___ ... ...... ................ ..12

5-9 Results for the insulated flask test for sand. ............. ...............124....










LIST OF FIGURES


Fiare page

1-1 Graphical depiction of stress exceeding the strength within a certain region of mass
concrete. .............. ...............21....

1-2 Temperature effects on fully insulated mass concrete. ................... ...............2

1-3 Relative humidity effects on fully insulated mass concrete. ........._. ..... ..._._..........22

1-4 Depiction of heat flow in an insulated case. ............. ...............23.....

1-5 Depiction of moisture state in an insulated case. .............. ...............23....

1-6 Temperature effects on non insulated mass concrete in one dimension. ...........................24

1-7 Relative humidity effects on non insulated mass concrete in one dimension. ........._........24

1-8 Depiction of heat flow in a non-insulated case. .............. ...............25....

1-9 Depiction of moisture flow in a non-insulated case............... ...............25..

1-10 Set up of the transient state calorimeter. ...._. ......_._._ .......__. ..........2

1-11 Set up of the insulated calorimeter. ........._. ...... .... ...............26.

1-12 Loading scheme for the third point beam test, and accompanying moment diagram. ......27

3-1 Vertical temperature gradients vs. time, within a dam lift. ........._._ .... ...._............73

3-2 Vertical temperature gradients vs. time, between several lifts. ............. ....................73

3-3 Effect of minimum dimension and replacement % of fly ash on temperature rise............74

3-4 Effect of minimum dimension and replacement % of BFS on temperature rise. .............74

3-5 Thermal constraint device. ..........._ ..... ..__ ...............75...

3-6 Effect of internal relative humidity on capillary tension. ..........._.....__ ..............75

3-7 Compressive strength vs. time of heat exposure. ....._._._ .... ... .__ ......._._........7

3-8 Elastic strain vs. time of heat exposure. ...._. ......_._._ .......__. ..........7

3-9 Graphs depicting compressive strength for concrete subj ect to high temperature. ...........77

3-10 Graphs depicting the elastic modulus for concrete subj ect to high temperature. ........._....77











3-11 Concrete tension specimen. ............. ...............78.....

3-12 Concrete specimen with notches ................. ...............78........... ...

3-13 Large and small specimens. ............. ...............79.....

3-14 A simple two-piece mould, with claw-like embedments ................. ........................79

3-15 The IDT test, with a sample of asphalt concrete. ......___ ..... ... __ ....._ ......8

3-16 Sectional view of the nitrogen gas test, with a diagram of principle stresses. ................80

3-17 Typical stress-strain curves for concrete in tension. .............. ...............80....

3-18 Kelvin chain model .............. ...............81....

3-19 Schematic drawing of a calorimeter used to measure specific heat............... .................81

3-20 Schematic drawing of a calorimeter used to measure thermal diffusivity. ................... .....82

3-21 Schematic drawing of a calorimeter used to measure the heat of cement hydration. ........82

4-1 Theoretical stress and strain distribution through cross section .............. ....................92

4-2 Loading scheme and moment diagram. ............. ...............93.....

4-3 Loading scheme for the measurement of elastic modulus in compression, with the
use of extensometers. .............. ...............93....

4-4 Comparison of methods used to obtain compression elastic modulus for concrete.
This plot depicts three day samples. ............. ...............94.....

4-5 Typical plot of 1-day stress ................. ...............95....... ...

4-6 Typical plot of 3 -day stress ................. ...............96........ ...

5-1 Set up of the transient state calorimeter. ......... ......._.__._ ......... .........12

5-2 Extrapolation technique to acquire the temperature change of the concrete. .................. 125

5-3 Set up of the insulated calorimeter ................. ...............125........... ..

5-4 Average temperatures (oC) for the point of 622 seconds .................... ............... 126

5-5 Average temperatures (oC) for the point of 623 seconds ................. .......................127

5-6 The specific heat is obtained by averaging the final five values that were obtained by
using the moving average method. ............. ...............128....











5-7 Typical extrapolation technique used for the transient test, in order to obtain AT2........129

5-8 Moving average for a 7 day cement paste sample. ............. ...............129....

5-9 Typical curves depicting the establishment of thermo-equilibrium within the flask
calorimeter, in using concrete specimens. ............. ...............130....

5-10 The evolution of concrete specific heat with age, in using the moving average
method............... ...............130

5-11 Hydration sketch of microdiffusion of free water through layers of already formed
hydrates to unhydrated cement. ............. ...............131....

5-12 Typical curves depicting the establishment of equilibrium for the paste samples
within the fl ask calorimeter. ............. ...............13 1....

5-13 The evolution of cement paste specific heat with age, in using the moving average
analysis method. ................. ...............132_._._.......

5-14 Curves depicting the establishment of thermo-equilibrium for lime rock within the
fl ask calorimeter. ........._.__...... ._ __ ...............132....

5-15 The results obtained from 5 individual specific heat runs for lime rock. ........................133









Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Engineering

THE DEVELOPMENT OF THERMAL AND MECHANICAL PROPERTIES FOR MASS
CONCRETE

By

Samuel J. Smith

December 2007

Chair: Bjorn Birgisson
Major: Civil Engineering

Our study was aimed at contributing to the development of design parameters for mass

concrete. It consisted of the assessment, procedural development, and testing for mechanical and

thermal properties that are relevant to the cracking of mass concrete at early ages. With this

assessment, it was chosen to develop the methodology behind testing for the elastic modulus,

modulus of rupture, tensile strain capacity, and specific heat. In addition to concluding on the

tests' viability, another obj ective was to evaluate these properties of concrete at a young age.

The flexural test that was developed for early age concrete utilized third-point loading with

surface mounted strain gages. The tensile strength and elastic modulus in tension and

compression increased, and the tensile strain capacity decreased from 1 to 3 day tests. The elastic

modulus of the compression region in the beam compared well to the estimated elastic modulus

from the compressive strength using the equation indicated in ACI 8.5.1-2002, and the measured

elastic modulus from compression cylinders. The tensile elastic moduli were generally lower

than the elastic moduli in compression and is thought to be due to micro-cracking within the

tension region at an early stage in the loading process. The observed difference between the

measured strains in the tensile zone versus the compressive zone warrants further investigation

into this area.









The specific heat of early age concrete and its components were measured with the use of

an insulated dewar flask. The lime rock, cement paste, and concrete were adequately measured

using the 11 value moving average analysis. The concrete and cement paste specific heat

increased with age, and is thought to be due to the diffusion of excess water into the pore

structure where the cement has previously undergone hydration. While the lime rock worked

well for the insulated flask test, higher variability was obtained for the sand samples due to it

requiring less mass and a longer duration of equilibrium time.









CHAPTER 1
INTRODUCTION

1.1 Problem Description

Mass concrete has been defined as an element having dimensions large enough to raise

concerns with respect to the heats of hydration, which cause significant volume changes and

therefore cracking within the structure. Although there are several methods that have been

developed in order to assess the vulnerability for a mass concrete structure to crack, there are few

models that are able to comprehensively assess mass concrete's thermal and mechanical behavior

on a finite scale.

The goal for this research was to work on the first step of developing this comprehensive

model, which included a thorough literature review and the development of a specific heat and

flexural test that could be used for early age concrete and its components. The literature review,

which covers a broader base than the experimentation that was conducted in this research, was

aimed at developing an approach to solve this problem by including the study of various thermal

and mechanical properties that are relevant to the cracking of concrete at an early age.

The reason for the development of these tests is to use them to quantify properties

individually, and to later integrate them into a finite element program to predict the onset of

detrimental cracking. Other essential parameters that were identified and studied, but were not

tested for include autogenous shrinkage, coefficient of thermal expansion, thermal diffusivity,

and heat production (from a calorimeter). All of these properties are essential in the development

of this finite element program because they encompass the generation and movement of heat,

and how it is associated with the mechanical behavior.










The mechanical behavior which raises concern with respect to mass concrete is cracking.

The concrete will crack when the tensile stress exceeds the tensile strength. These stresses may

be induced by humidity and temperature factors, as indicated in Equation 1-1.

o- = E (ez, + ez,, ec,, (1-1)



In this equation, Est is the strain due to temperature and Ssh is the strain due to capillary

shrinkage. In addition, the creep strain, scr, reduces the overall stress accordingly (Figure 1-1).

The temperature and relative humidity gradients that develop within mass concrete are the main

factors that cause cracking. The following two cases introduce the fundamental issues that are

associated with these factors.

1.2 Fully Insulated Case

Regions of concrete in its elastic state may expand or contract due to temperature and

relative humidity. Generally, a homogenous state of humidity and temperature within concrete

does not induce strain, unless there are obstructions within or outside of the mass causing

restraining forces against a uniform expansion or contraction. In order to achieve nearly

homogenous relative humidity and temperatures (and therefore minimum strain), insulation may

be used to prevent heat and moisture losses. In the case where a concrete block is fully insulated

(and externally unrestrained), as in Figure 1-2 and 1-3, temperature and humidity gradients are

nearly eliminated. However, this may not completely dismiss cracking, as humidity-related strain

may become an issue (Figure 1-3). Autogenous shrinkage may be a harmful mechanism, and is a

result of the hydrating cement paste consuming the water within the concrete matrix. Although

the figures included in this chapter summarize the potential consequences in mass concrete, they

may be studied in much more depth in Chapter 3, Literature Review.










In the insulated case, there is only a slight temperature differential that develops within the

mass, as depicted in Figure 1-4. Although this is one of the most effective ways of reducing the

risks of thermal cracking, it has been found that especially when using high early strength

concrete, there may be too much heat produced at an early age. This may cause a couple of

potential conflicts, including the formation of delayed ettringite (at a later stage) or a weaker

concrete matrix of co-dicalcium silicate hydrate (immediately after hydration).

With respect to autogenous shrinkage, regions will contract due to their porous nature and

relative humidity (RH), as the water in a concrete mixture reacts with the Portland cement. The

capillary stresses that may be experienced by a region within an insulated mass concrete block

may be brought about by autogenous shrinkage gradients, as indicated in Figure 1-3 and 1-5.

The RH is simply the partial water vapor pressure divided by the saturation water pressure,

as shown in Equation 1-2. It will adjust due to either a change in the partial pressure of vapor, or

a change in temperature (which causes a change in the saturation vapor pressure).


RH (%/) = [FtrVpr*10(1-2)


The Kelvin equation, that describes the change of vapor pressure over a liquid curved with

a radius r (such as in a capillary) may be written as follows,


M I trnpr2- (1-3)
Psat,,mton r -R -T

where y is the surface tension; y,,, the molar volume; R, the universal gas constant; r, the radius

of the droplet; and T, the temperature.

By equating the Kelvin and Laplace equations and substituting RH of Equation 1-2 into

Equation 1-3, we can calculate capillary tension as depicted in Equation 1-4.









In (RH )RT
GCaplllan.= (1-4)

1.3 Non-Insulated Case

In the case where insulation is not used on one face, the differential relative humidity and

temperature between regions is more pronounced and may cause cases of conflicting expansion

and contraction, and therefore strain. It is when these regions hold different conditions with

respect to temperature and humidity that a coupling of the behavior may lead to the most

ominous of stresses. If we were to look at one particular region, say region 3 of Figure 1-6 and 1-

7, the total strain of this region is that which is induced by both temperature and humidity. In the

case depicted in Figure 1-7, the relative humidity of the air is at much less than 100 %, and

therefore encourages drying shrinkage. In the case where the concrete is kept at 100% relative

humidity, the effect of relative humidity restraint may often times be considered negligible, as

long as autogenous shrinkage is not significant.

The thermal behaviors of concern within mass concrete include both heat movement, and

heat production. As Figure 1-8 shows, Fourier' s law of cooling governs the movement of heat

from the concrete block to the ambient air. Fourier' s law of cooling is indicated by the following

equation,


dO=-k VT -dS (1-5)


where Q is the amount of heat transferred, t is the time taken, k is the material's conductivity, S

is the surface through which the heat is flowing, and Tis the temperature.

The heat production within the mass is a property that may be measured with the use of a

calorimeter, where the temperature is measured with respect to time within a concrete or paste










sample of known mass. The reaction of cement and water is exothermic, and therefore is

accelerated with the addition of heat (Figure 1-8).

Analogous to the Fourier' s law, Kelvin's equation (depicted previously) may not only be

used to describe the stress induced on the capillary matrix, but also the tendency for the moisture

to migrate or evaporate. As the relative humidity of the surrounding air becomes less, there is

more of a tendency for moisture on the face of the specimen to evaporate. In addition to this, as

seen in Figure 1-9, moisture may be inclined to move from the central region towards the outer

region if it is able to migrate through the capillary network within the concrete.

1.4 Tests Developed

The main objectives of this research were to develop a flexural and specific heat test.

Although these properties have been studied, there aren't any standards that describe how they

may be applied to early age concrete. A methodology was developed for both tests, so that the

procedures may be applied to concrete at an early age.

1.4.1 Specific Heat

Specific heat is a material's thermal property that describes the amount of energy it takes

to raise one gram of substance one degree of temperature. It is important because if the heat

production of the concrete (in units of energy) is known within a massive structure, than the

temperature rise within can also be calculated. Another thermal property that should not be

confused with specific heat is the thermal diffusivity of a material. The thermal diffusivity

describes the speed that a heat front may move through a material. Together, these two properties

can be used to calculate the thermal conductivity of a material by the following equation,

AZ= p- c-a










Where h is the thermal conductivity, c is the specific heat, and a is the thermal diffusivity.

Therefore, the specific heat is the first step in calculating the thermal movement within mass

concrete.

It was found in the literature review that the concrete's specific heat evolved with respect

to age (De Schutter and Taerwe, 1995). This is thought to be caused by the chemical reaction

between cement and water. As concrete ages, new products are formed and therefore contribute

to properties that evolve with time. The experiments conducted in this research were aimed at

looking into the evolution of this property, as the concrete aged.

In order to measure the specific heat, two separate calorimeters were developed. Within

each calorimeter included a stir paddle, a heater, and two thermocouples. The stir paddle was

used so that equilibrium could be achieved within. This was necessary because the specific heat

is based on the amount of energy it takes to raise the temperature of a substance one degree.

Therefore, by measuring the heat energy outputted, this could only be related to the specific heat

if it was assumed that all of the components within the calorimeter achieved equal temperatures.

The heater' s output was measured by a watt meter, that plotted the power in watts as a function

of time. A numerical method could then be used to calculate the energy in kiloj oules. The two

thermocouples within the calorimeter were read by a portable data acquisition system. Both the

energy measurements and thermocouple readings could be uploaded and analyzed in excel.

The two calorimeters that were developed included one that was based on work done by

De Schutter and Taerwe, 1995, (a transient temperature analysis) and another one that was

developed by the researcher (an insulated analysis). The transient experiment utilized two baths,

where one was placed within another (Figure 1-10). The exterior bath was of the circulatory

type, and was set to maintain a constant temperature of 280C, which was that of the room










temperature within the lab. The interior bath was made from stainless steel and contained all of

the components as indicated in Figure 1-10. During and after heat was supplied to the interior

bath it was readily dissipated to the exterior bath' s constant state of 280C. This transient state of

heat loss was analyzed and the specific heat was ultimately calculated, as will be discussed

further in Chapter 5.

The insulated test included the use of a high vacuum (107 torr) dewar flask, as indicated in

the schematic of Figure 1-1 1. This procedure was developed in order to contain all of the heat

added to the calorimeter. It also served to better observe the thermal equilibrium of the

components within the flask, as this was not as clear as with the transient state of the previous

experiment. As Figure 1-11 indicates, the setup within the insulated calorimeter is identical to

that of the transient state set up. In order to carry out a single run to analyze a material's specific

heat, both a calibration test and material test were needed for each experiment. This will also be

described in more detail in Chapter 5.

1.4.2 Flexural Test

The development of a test that can accurately indicate the mechanical behaviors of mass

concrete is a critical contribution to modeling it on a finite scale. Unlike the specific heat tests,

which measure a single thermal property, the flexural test is used to measure three critical

properties. These include the modulus of rupture (MOR), tensile strain capacity, and elastic

modulus in tension and compression. While the MOR estimates the stress at which concrete may

fail in tension, the tensile strain capacity is defined as the strain at which concrete will fail.

Furthermore, the elastic modulus is a property that is indicated by the amount of stress that a

material undergoes with a unit strain applied.

While mass concrete may often times contain thermocouples, these temperatures may be

used to ultimately indicate the thermo-mechanical movement of mass concrete. While the










expansion or contraction can be calculated with the coefficient of thermal expansion, the tensile

strain capacity may be used to check the status of a certain region. The elastic modulus can also

be used to indicate what the stress state is for a given strain.

Like the specific heat test, the flexural test needed to be compatible with early age

concrete, and additionally it needed to be applied in order to study changes in mechanical

properties at different ages. It was decided that the third point loading scheme would be used for

this proj ect. This included capturing the magnitude of load with a load cell, and the magnitude of

stain with two strain gauges. One strain gauge was placed on the top surface and the other on the

bottom surface, in order to measure compressive and tensile strain, respectively. The stress

versus strain relationship was used to obtain the elastic modulus in tension and compression by

calculating the slope of the initial linear portion of this graph. Efficiently, four important

properties were obtained from this test. The loading scheme is indicated in Figure 1-12.

1.5 Main Objectives of Study

The main objectives of our study included the development of a mechanical and thermal

property test for early age concrete. More specifically, this includes the following:

* The evaluation of the use of a beam test for the determination of tensile strength, elastic
modulus, and tensile strain capacity of concrete at an early age.

* The evaluation of test methods for the determination of specific heat of early age concrete.

1.6 Scope of Work

The scope of work performed in this study includes the following:

* Survey of specifications A review of various department of transportation and
government agency guidelines and specifications involving mass concrete.

* Literature review.

* Performance and evaluation of compression and flexure test.










*Evaluation of specific heat test and conduction of test on aggregates, cement paste, and
concrete.






E = tensile modulus
at = strain by temperature
~esh = strain by rel. humidity
scr = reassociation by creep


Graph represents
one particular
C n region


StreSS


Strength
/Induced Stress
= E*(st+Esh-scr)


Pllasicl StatElastic Statc



Figure 1-1. Graphical depiction of stress exceeding the strength within a certain region of mass
concrete.















+6t = expansion, w.r.t. temp
-6t = contraction, w.r.t. temp


Due to uniform
thermal expansion,
there will be
no area of
notable restraint.


The fully insulated specimen will
undergo complete, relatively
uniform expansion and contraction
due to temperature. Later on, the
specimen may be threatened by
DEF, and a weaker matrix of
ac-dicalcium silicate hydrate (high
temperature effects).


Figure 1-2. Temperature effects on fully insulated mass concrete.


tah = expansion, w. r.t. humidity|
-dh =contraction, w.r.t. humidity



li. ..dull
... *~~ i radient


Indicates region
of hig hest g radilent
(i~e.,strain


lNote: The scale for 6h in this case is
much smaller than in the
non-insulated case and is almost
completely due to autogenous
shrinkage.


The core will have a hig her
temperature than the shell
region. This causes faster
hydration, and therefore the
core will reach the stage of
autogenous shrinkage quicker
than the shell (causing
restraint). Autogenous
shrinkage is a humidity effect.


Figure 1-3. Relative humidity effects on fully insulated mass concrete.














Only slight
heat dissipation.


Slightly Cooler



Slighitly Hlotter


Figure 1-4. Depiction of heat flow in an insulated case.




More maturity due to
slightly higher temperatures
cyclically accelerating hydration
due to heat production. Therefore,
this area will be the first to
undergo autogenous shrinkage
and may develop internal restraint.


Approx. 100%


Figure 1-5. Depiction of moisture state in an insulated case.












+6t = expansion, w.r.t. temp
-6t = contraction, w.r.t. temp


Indicates region
of highest gradient


1~
2r
3


gradient


--Gradient

*~"'"Expansion


Figure 1-6. Temperature effects on non insulated mass concrete in one dimension.



+6h = expansion, w.r.t. humidity
-6h = contraction, w.r.t. humidity +6h
Indicates region
of highest gradient,
i.e. strain_ 2 - - -


5 t

Harmful Stri

7 I=:::_ Gradient

SNote: Sh is dominated by drying
shrinkage in this case (not
autogenous). In this diagram, we
assume that the
relative humidity of the
air is at less than 100%


Figure 1-7. Relative humidity effects on non insulated mass concrete in one dimension.












Heat flow to air, due to Fourier Law
of Cooling. More heat flow due to
relatively low exterior temperature.
Evaporation endothermicc process)
also contributes to cooling.


-In addition to heat being
able to readily dissipate
from a non-insulated top,
this region is cooler due
to less hydration occurring
(lower moisture).



Migration of heat
--- from hot core,
to cool shell (Fourier).


Cooler Region



Hotter Region


More hydration due to
higher temperatures and
a more humidified
environment cyclically
accelerates hydration due
to heat production.


Figure 1-8. Depiction of heat flow in a non-insulated case.



Moisture evaporation, due to
Kelvin's law. More evaporation due
to relatively high exterior
temperature and low moisture.
Moisture migrationros :,em :,a'l L


a lower exterior
humidity drives it
in this direction
(Kelvin). -


Dryer (<100%)


Approximately
100%


Figure 1-9. Depiction of moisture flow in a non-insulated case.

































Figure 1-10. Set up of the transient state calorimeter.


Figure 1-11. Set up of the insulated calorimeter.








































Figure 1-12. Loading scheme for the third point beam test, and accompanying moment diagram.


II L I



M=PL/6









CHAPTER 2
SURVEY OF SPECIFICATIONS

2.1 Introduction

According to ACI Committee 207 (2005), "Mass concrete is any volume of concrete with

dimensions large enough to require that measures be taken to cope with the generation of heat

from hydration of the cement and attendant volume change to minimize cracking." ACI' s

definition was made to be ambiguous because there are infinite combinations of mix designs,

geometries, and ambient conditions that may lead to cracking in mass concrete. However, most

states have set their own guidelines that classify mass concrete as having minimum dimensions

at or above a certain threshold, usually in the range from 4 to 5ft. Unites States agencies, such as

the Army Corps of Engineers and the Bureau of Reclamation also have guidelines and perform

their own experimentation to determine certain parameters to follow.

2.2 State Specifications

There were seven states that were surveyed by observing their current mass concrete

specifications and provisions. These states included California, Colorado, Delaware, Florida,

iowa, Virginia, and West Virginia. All of these states had specifications addressing several

important requirements for the construction and engineering procedures involving mass concrete.

The regulated parameters included allowable temperature gradients, allowable peak

temperatures, and limits involving mineral admixtures. The specifications also included a

description of what it is that constitutes mass concrete and construction procedures that need to

be followed during the curing process.

Any structure which has a minimum dimension above the state code's threshold is

considered mass concrete, and actions are taken in order to reduce both the temperature gradient

and peak temperature in accordance with the state specifications. A specialty engineer is often









hired by the contractor to decide on a safe temperature range, to design the mix, and also to help

monitor the temperatures. Typically, the monitoring program involves putting at least two sets of

interior and exterior temperature probes (e.g. thermocouples) within each mass concrete element.

Generally, the most practical way to limit temperatures includes the replacement of

Portland cement with fly ash or ground blast furnace slag. The measures taken to reduce the

temperature magnitude and gradient are discussed in more detail in the literature review.

Although the specialty engineer often has a good idea about the most effective mix design, some

states specifically indicate certain limits on mineral admixtures. Some specifications may be

ambiguous, due to them only mentioning a maximum amount of admixture, but not specifying a

recommended range. It is evident in Table 2-2 that there are various ranges or specified

maximum amounts of admixtures to replace cement with. This is partly attributed to the

variability in admixture properties when obtaining the product from different locations. In fact,

West Virginia' s provisions indicate that multiple sources of the same type of pozzolanic material

are not permitted within the same structure.

For some mass concrete structures, additional effort must be made in order to limit thermal

cracking. Mentioned by the Delaware specifications, the use of insulated forms and curing

blankets help there to be a uniform distribution of temperature. One method of reducing the

temperature magnitude involves using cooling pipes within the mass during the hydration period.

California Transportation Department mentions this technique for use in the more massive

applications, but requires that the pipes must be fully grouted after the cooling is completed.

Cracks may occur in massive structures, either due to the negligence of the contractor, or

because of the complexity of the situation. For cracks of small magnitude, between 0.01" and

0.02", the specifications from Colorado, Virginia and Delaware require them to be epoxy










inj ected. This method is used because the main concern lies in the concrete's ability to resist the

ingression of deleterious elements that may be a precursor to structural failure. Another

important reason for epoxy inj section is to beautify the appearance of portions of the structure that

can be viewed by the public. As the Virginia specifications mention, it is also important for the

excess mastic compound to be removed and for the surface to be made visually uniform. In cases

where the cracks are more extreme due to the contractor exceeding the temperature control

requirements, then the contractor may be ordered to remove and replace the concrete at no

additional cost to the proj ect.

It can be seen in Table 2-1 that most DOT's specify a maximum curing temperature of

around 160 F. This temperature is chosen due to extensive research that has found delayed

ettringite formation (DEF) to occur after concrete has been subj ected to temperatures around

175 F (Nasser and Lohtia 1971, Ramlochan 2003, Ramlochan 2004). At times, a rather large

deduction in pay will be implemented against the contractor if the specified limit in temperature

is exceeded. For example, the mass concrete specifications for a bridge in Colorado (proj ect

number HB-0821-075, Apr. 28, 2005) indicated that if the temperature of concrete exceeded

11' F or more above 165 F, then the bid price for concrete would be deducted by $200.00 per

cubic yard of concrete. The fines were reduced for temperatures that were less above the

maximum, starting at a deduction of $3.00 per cubic yard for temperatures from 0-4 F above

the limit.

With respect to temperature differential, it is not an issue of chemical consequences, but

rather one of conflicting mechanical behavior of regions within the mass. Caused by a non-

uniform temperature profile, conflicting mechanical behavior occurs due to variations in thermal

expansion. The "Max Differential" column in Table 2-1 refers to the maximum difference in










temperature allowed between the hottest and coolest temperature monitoring probe taken from a

section. These values are based on experimental and field data where it was found that a certain

magnitude of temperature differential caused cracking. Delaware' s specification was more

comprehensive (see Table 2-1), in that the maximum allowable temperature difference was

higher as the concrete became more mature.

2.3 Government Agencies

2.3.1 U.S. Army Corps of Engineers

The U. S. Army Corps of Engineers is responsible for various civil engineering proj ects in

the country. They're involved with designing and managing the construction of military facilities

for the Army and Airforce. In addition to this, they also design and operate water resource and

civil work proj ects. As a result, they have designated their own guidelines that are somewhat

different from the states' DOT specifications. Their guidelines include special provisions

discussed by ACI Committee 207 (2005) in order to counteract thermal cracking. The following

list describes what additional measures are taken in mass concrete, when compared to the

construction procedures of non-massive concrete:

* Changing construction procedures, including placing times and temperatures.
* Changing concrete materials and thermal properties.
* Pre-cooling of concrete materials and controls on concrete placement temperature.
* Post-cooling of concrete.
* Construction of joints (with waterstops where necessary) to control location of cracks.
* Alteration of structure geometry to avoid or control cracking.
* Use and careful removal of insulation


There are three levels of analyses that are used by the U.S. Army Corps (U. S. Army Corps

1997) when designing a structure that is potentially considered massive. In order to assess the

vulnerability of cracking for a mass concrete structure (MCS), level one analysis is used to make

a conservative guess and to determine if a more detailed analysis is necessary. It involves little or










no laboratory testing and assumes the worst reasonable combination of material properties and

site conditions. Strain, length change, and cracking are computed based on temperature change in

the MCS. In addition, an assumption of complete restraint of thermal expansion is made.

For the level two analysis, thermal analysis is based on a more rigorous determination of

concrete temperature history by the use of several analysis tools. The temperature history of

concrete may be estimated by the use of 2-D (cross section) or 1-D (strip) finite element analysis,

or Schmidt and Carlson methods. An evaluation of the cracking involved within the interior as

well as the cracking at the surface is evaluated at this level.

Level three analysis involves detailed cracking evaluation of complex shapes and loading

conditions other than thermal loads. Usually performed exclusively with the finite element

method, efforts is first put forth in order to collect environmental data, assess and implement

applicable construction parameters, and perform the testing required for thermal and nonlinear

material property input. This analysis involves a 3-D finite element model, and requires much

more time than the other methods.

2.3.2 U.S. Bureau of Reclamation

The U. S. Bureau of Reclamation is best known for the dams, power plants, and canals it

constructed in the West. They constructed more than 600 dams, including the Hoover Dam on

the Colorado River and the Grand Coulee Dam on the Columbia River. Due to their involvement

in dam construction, their method of crack reduction emphasizes the use of cooling pipes.

John Laboon, U. S. Bureau of Reclamation, was able to provide literature (Townsend 1981)

that displayed the plans of the elaborate cooling system involved in the construction of the Glen

Canyon Dam. Generally, it consisted of pipe or tubing placed in grid-like coils over the entire top

surface of each 5 or 7 V/2 foot lift of concrete. Aside from the embedded pipe cooling system,










another method included reducing the placing temperature of concrete. Although the average

recommended cooling temperature is 500F, it has been reported to be as high as 650F.

The bureau also finds it important to evaluate the cracking on the surface of mass

structures, after they have been poured. Cracks that begin to raise concern include those that are

more than 0.01 in. Similar to state guidelines, the bureau usually specifies that such cracking

needs to be filled with a special epoxy agent.


Table 2-1. Limiting conditions, indicated in mass concrete specifications taken from various
DOT' s.
Constitution of Mass
State DOT Max Temp (Deg F) Max Differential (Deg F)
Concrete
West
Min Dimension of 4ft. 160 35
Virgimia

Virginia Min Dimension of 5ft. 170 w/Slag, 160 w/FA. 35
Min Dimension of
lowa 160 35
3.9ft.
Florida Specified by specialty Specified by specialty 3
engineer. Engineer.
Determined
.48hrs =40F,
Delaware sujetvl n160 Next 2-7 Days = 50F,
a proj ect to proj ect
basis.Next 8-14 Days = 60F.

Colorado Min Dimension of 5ft. 165 45

.i ienino Specified by the thermal control
California 6.f.160 plan, provided by the
contractor.









Table 2-2. Required amounts of mineral admixtures, indicated in mass concrete specifications
taken from various DOT's.
Required Mineral Total Required
Fly Ash Required Slag Required (%
Admixture Cementitious
State (% Replacement Replacement of .aera
Replacement Of Mael
of Cement) Cement) 3eet(/)(bf'
WVA 25% (Max) 50% (Max) 50% (Max)
VA 25-40% 50-75%

IA 35% 20.79

FL 18-50% 50-70%

DEL -75% (Max) 75% (Max)

CO

CA ---18.73









CHAPTER 3
LITERATURE REVIEW

3.1 Overview of Issues with Mass Concrete

As more foundations and dams were poured from concrete in the United States during the

twentieth century, much attention was directed towards mass concrete, and the problems

associated with it. The complications corresponding with mass concrete included excessive

cracking thought to be brought on by high temperatures. This speculation led to several studies

during this time, in order to pinpoint the issues.

Mead (1963) presented a data analysis of Pine Flat Dam, where the temperatures were

monitored within and between successively poured lifts. When this dam was constructed, it was

decided that it would not only serve as a retention structure, but also as a study to determine the

effects that the hydration, geometry, and environment have on the heats produced within mass

concrete. Electrical resistance thermometers were embedded throughout, and were able to

illustrate temperature profiles. The dam was poured in lifts in order to allow the concrete to cool

in increments and therefore not produce high temperatures in concentrated areas (Figure 3-1). It

should be noted how the differential temperatures peak at a certain time, and then converge to

zero. Figure 3-2 shows the typical temperature profile between successive lifts, where at least a

5 day curing period takes place before each proceeding lift placement. It can be noticed that the

initialization of each successive lift causes the preceding lift to fluctuate in terms of temperature.

The hypothesis made by these researchers was that cracking would be present where the

monitored thermal gradients would reach excessive values. At the time of this publication, it was

still uncertain what was to be considered "excessive." By observation of Figure 3-1, it can be

seen that the internal gradient does not exceed 10 F in this lift, and as a result there was no









cracking depicted in this lift at early ages. With the specifications of today, one may have been

able to say that this differential is in fact safe for the concrete.

In the years to come, more research was conducted, and it was confirmed that thermal

gradients due to the heats of hydration cause cracking in mass concrete (Burg and Ost 1994,

Burg and Fiorato 1999, Faria 2006, Kim et al. 2002, De Schutter and Taerwe 1995). The

conclusions brought about by these studies were derived from experiments which utilized more

enhanced instrumentation, microscopy, and software tools. In addition to this, findings from

researchers with respect to the degree of hydration of concrete and associated heat flux, as De

Schutter and Taerwe (1995) found, helped to lead to accurate models which could be used to

predict the temperature profiles and stresses in later work (De Schutter 2002). Ballim (2003)

successfully implemented a finite difference model in order to predict the temperature curve at

different locations within mass concrete, as this will be discussed in more detail later.

In addition to thermal gradients, relative humidity gradients and high temperature curing

have also been found to pose detrimental effects on concrete. Mechanically, humidity gradients

may act similarly to thermal gradients in order to cause differential contraction and ultimately

lead to cracking (Grasley 2003, Bentz and Jenson 2004, Lee et al. 2006, Ulm and Coussy 1995).

In contrast to the effects of gradients, high temperature curing may cause alternative chemical

reactions to take place, creating compounds which are inferior to those produced at more

moderate temperatures (Nasser and Lohtia 1971, Mindess et al. 2003, Ramlochan et al. 2003,

Ramlochan et al. 2004).

3.2 Heats of Hydration

The hydration of Portland cement is an exothermic reaction which may produce

temperature rises as high as 50 C in mass concrete. It consists of combining the compounds of

Portland cement with water and producing hydration products. Because the reaction is









temperature dependant, the climbing temperature accelerates the reaction and the concrete may

set at even hotter temperatures than expected. Ulm and Coussy (1995) suggest that as the

reactions proceed, the water diffuses through the cement from the regions of the hydrated cement

to the regions of unhydrated cement, where products form on an instantaneous manner, relative

to the timescale of the diffusion process. With respect to reaction kinetics, the diffusion of water

is said to be the most dominating mechanism of the hydration reaction (Ulm and Coussy 1995).

The hydration reactants consist of compounds within the cement which react at different

rates, release different amounts of heat, and contribute differently to strength (Table 3-1). It

should be noted that the C3A + CSH2 aS Well aS the C3S, contribute the most to the cement's heat

lib erati on.

3.2.1 Temperature Prediction in Mass Concrete

Ballim (2003) developed a two dimensional finite difference model to predict the

fluctuation of temperature with respect to time. His predictions were found to be within 2 C of

actual temperatures. Like Ulm, Ballim knew that an important problem facing heat modeling is

that the rate of heat evolution in a specific element depends on mixture parameters, time, and

position within the mass. After determining the rate of heat liberation of the material by use of a

calorimeter, the Arrhenius maturity function was used to predict the rate and extent of hydration

at any time and position within a block which was 700 x 700 x 1000mm.

Ballim's model (2003) was essentially based on the two-dimensional flow of heat (the

third dimension being insulated) as well as the maturity of concrete with respect to time. The

heat flow within a porous medium may be described by the Fourier equation,



pC 2+ Q (3-1)










where p is the density of concrete; Cp, the specific heat capacity; T, the temperature; t, the time;

k, the thermal conductivity; x and y, the coordinates at a particular point in the structure; and Q',

the rate of internal heat evolution.

The rate of heat evolution, Q', is based on the equation for obtaining the total heat Q from

calorimeter tests, noted as the following:

Q = mC ST (3-2)

where m is the mass of the sample and ST is the change in temperature of the sample over the

time period under consideration. The rate of heat evolution is therefore derived as the following:


Q', =(3-3)


However, Ballim (2003) realized that although Equation 3-2 factored in the temperature

change, its derivative in Equation 3-3, does not account for the effect which temperature

magnitude has on the rate of the reaction (ie., the production of heat). Therefore, it is essential to

adjust for this factor, as the temperature magnitude is constantly changing and affecting the

reaction rate of the medium. In order to predict the heat liberation accurately, one needs to

express the heat rate equation in terms of the maturity time, rather than real-time. Therefore, the

Equation 3-4 expresses the maturity-based heat rate which is used to account for the exothermic

nature of the reaction.

dQ
Q'M (3-4)


The heat rate equation in terms of real time is needed in order to calculate the flow of heat,

as indicative of Equation 3-1. It is derived by using the chain rule and is noted as the following:


Q', = Q', *- (3-5)









The maturity equation which has been proven effective by Ballim's (2003) work is the

Arrhenius relationship. It is crucial to Eind the change in heat with respect to maturity time, in

order to accurately depict the rate of heat liberation at individual time frames. The following

equation depicts the Arrhenius relationship.


t201 1 (3-6)
,=>i- Ri 273 + To T

In this equation, t20 is the time required when curing at 20 C to reach equivalent maturity of an

insitu element. Ti is the average concrete temperature (K) in the time interval Ati, To is the

reference temperature (taken as 20 C), and E is the apparent activation energy (- 34 kj/mole).

By using the Arrhenius relationship, one is able to calculate the effective maturity of the concrete

and apply this value to the time-based heat data received from the calorimeter, in order to

indicate the rate of heat liberation by Equation 3-4 and 3-5 above.

When situations arise where there will not be significant thermal gradients or extreme

temperatures, than the heats of liberation are usually not of concern. However, how should we

indicate what is or isn't mass concrete? It is noticeable that there is little agreement between

different state specifications for what is considered mass concrete. This is because there are

many factors which contribute to heat production, including ambient temperature, mixing

temperature, and cement type variability. Bamsforth (1984) specifies that for sections in excess

of 2m (6.6ft), temperature rise is directly proportional to the cement content. He had also noted

that the heats from hydration in mass concrete become increasingly an issue when the cement

content is greater than 350kg/m3 (22 lbs/ft3). However, as high-strength concrete has become

more utilized in recent years, it has raised further concerns, due to its propensity to producing

more heat than normal strength concrete. This has also led to increased uncertainty of the









dimensional thresholds set by the states, due to higher temperatures leading to problems at

smaller dimensions. Bamsforth (1984) mentions that for a section that is less than 500mm thick,

it is usually assumed that heat is readily lost to the environment and does not cause significant

internal thermal restraints. Ulm and Coussy (2001), on the other hand indicate that the hydration

heat diffusion length may be determined in order to decide whether or not a structure should be

considered massive. The following equation depicts his theory on the gauge-length, 16,


lh = Ju,(3-7)

where D is the thermal diffusivity and zh is the characteristic hydration time. The value zh is

considered intrinsic to the material (respectively to the mix proportions of the material). In Ulm

and Coussy's work (2001), they find that the gauge-length where the latent hydration heat affects

the long-term structural integrity for high performance concrete is when 16 = 0.2m, while in

normal strength concrete, lh = 0.3m.

3.2.2 Low Heat Cements

In order to account for the large amounts of heat generated within massive structures where

high strength concrete was not needed, Type IV cement was developed in order to lessen the heat

production. Type IV cement is produced with less C3A and C3S, in order to relieve the concrete

from arduous stresses brought on by large amounts of heat (Mindess et al. 2003). However, it

was found that by only reducing the amount of C3A content (and not as much C3S) and fine

adjusting the other components accordingly, it poses as an effective and efficient solution. Less

C3A content not only produces a lower adiabatic temperature rise during hydration, but also

produces higher sulfate resistance. While lowering the C3S amount may have a similar impact on

heat generation, the high early strength of concrete can be reduced substantially (Mindess et al.

2003). In considering the types of Portland cement to be used, it can be found that Type IV









cement (Low Heat of Hydration), which has a considerably low C3S content, is nearly extinct

due to the latter explanation. For this reason, a Type II, 'Moderate Heat of Hydration,' or Type

V, 'High Sulfate Resistance,' is often used to replace it, where there is an adequate amount of

C3S available for early strength.

It should be noted that a lower rate of hydration is the key to less heat generation.

Therefore, another efficient way to decrease the heat produced during the hydration process is by

replacing some of the Portland cement with mineral admixtures, which hydrate at a slower rate,

and ultimately contribute to lower peak temperatures within a curing mass. The most popular

mineral admixtures include ground blast furnace slag and fly ash.

3.2.3 Mineral Admixtures

In common practice, mineral admixtures may be used to either replace cement, improve

the workability of concrete, or to enhance the durability of concrete. When dealing with mass

concrete, mineral admixtures are often used for the same reasons, and especially for replacing the

cement content. Replacing cement with mineral admixtures that hydrate at a much slower rate

yields much less heat and also produces a denser and more tightly bound matrix (Malhorta and

Mehta 1996, Naik et al 1994, and Wee et al. 2000). Heat generation is dependent upon mineral

admixtures (as well as minimum dimension) in OPC concretes (Bamsforth 1984), as shown in

Figure 3-3 and Figure 3 -4. Notice that it is typically acceptable that larger amounts of Blast

Furnace Slag (BFS), rather than Fly Ash, may customarily be used to replace cement. Unlike Fly

Ash, BFS is a cementitious admixture, which means that it only needs water to react. Fly Ash

however, needs a combination of water and calcium hydroxide (from cement paste), in order to

produce calcium silicate hydrate. The weakness of mineral admixtures is that the strength gain is

much more gradual, and may lessen a structure's load capacity at earlier stages.









3.2.4 Other Methods to Lessen Heat

Other effects on heat generation include the pour size, the type of formwork, and the

mixing temp. In Figure 3-3 and Figure 3-4, the temperature rise with respect to minimum

dimension can also be seen. As it can be depicted in the graphs, the largest increase in

temperature rise occurs when the minimum depths range from 0.5m 2m in OPC concrete (the

curves are the flattest in this region). Pours that have a minimum dimension which is greater than

3 m to 4 m asymptotically reach a maximum temperature increase, which depends on the

admixture replacement percentage. This asymptote is due to the concrete nearly having full

insulation within itself at these higher dimensions.

The type of formwork or the use of insulation may also be a significant factor in

controlling the liberation of heat in a mass pour, but several factors should be accounted for with

respect to this. Plywood happens to have much better insulation properties than metal forms and

therefore may be able to serve as an insulator and lessen the changes in temperature from the

core to the exterior. Although forms may serve to moderate the temperature differential, it is also

important to consider the overall rise in temperature (Bamsforth 1984). By heavily insulating

concrete, it may result in the deterioration of the hydrated cement paste (HCP) properties at high

temperature (Ramlochan et al. 2003, Ramlochan et al. 2004). Thermal shock also needs to be

considered as these forms are removed, and the newly exposed surfaces cool to the surrounding

temperature. For the face of concrete which is exposed to the air, several types of insulation can

be used to lessen thermal gradients. Wetted quilts or burlap can not only serve as insulators but

also provide the concrete with essential moist curing conditions (Bamsforth 1984). Another

method is to use tenting, in order to prevent evaporative cooling. Tents are especially useful

when the open air has a relatively small amount of water content at a given temperature. This is

known as relative humidity, and when it is low it may cause deleterious evaporative cooling and









loss of water at the surface (Grasely 2003). Other forms of insulation include foam mats, soft

board, or sand laid on polythene sheets (Bamsforth 1984).

The mixing temperature is another factor that may lower the heats of hydration. By cooling

the mixing temperature, the heats generated during critical hydration periods are less. This can be

accomplished by using chilled water, ice, or cooled aggregates within the mix.

Cracking may still occur, even though insulation or plywood formwork is used, or the

mixing temperature is reduced. The term, "Mass Concrete," does imply that it is massive, and for

that reason, the predominant way to solve the problems of heat liberation lies in cement

chemistry and the nature of exothermic reactions.

3.3 Cracking

Cracking is one of the main concerns when considering the durability of concrete. It allows

ions to access the matrix with much less impedance and may lead to increased corrosion of the

steel reinforcement, more prevalent sulfate attack, and ultimately more vulnerability to structural

failure. As will be discussed shortly, the internal restraint of concrete is a cause for cracking, and

can be a result of temperature or relative humidity differences within its mass. These restraints

are what cause significant strains to develop because of the conflicting contraction rates.

However, the strains are not harmful unless they cause significant magnitudes of cracking.

The magnitude of cracking is determined by the thermal expansion coefficient of concrete,

the degree of restraint and the tensile strain capacity (Bamsforth 1984, Houghton 1976).

According to Bamsforth (1984), there are several practical ways to reduce the likelihood of

cracking within high volume pours, including the following:

* Reduce the peak temperature during curing
* Select aggregate with a low thermal expansion coefficient
* Minimize the restraint to thermal movement
* Increase the tensile strain capacity









Reducing the peak temperature usually moderates the differential temperatures within the

concrete and the overall temperature fall to ambient conditions. The overall fall of the mass is

important because it dictates the concrete's susceptibility to thermal shock and external restraint.

For this reason, the peak temperature is one of the most important attributes to control with

respect to thermal stresses.

During the construction of the Pine Flat Dam (Mead 1963), one of the control measures

taken in order to reduce the peak temperature was to keep the concrete cool before and during

the pour. In fact, there was a limitation set that the concrete had to be from 40 F to 50 F while

being placed. The way that they chilled the mix included screening the aggregates with cool well

water and refrigerating the other ingredients, except for the Portland cement. The target

temperature of the cooled components was at 3 5 F. When the ingredients all came together as

the concrete was being mixed, flake ice was added as well.

Another way to reduce cracking may be by selecting an aggregate with favorable

mechanical and thermal properties. In the case where an aggregate with a low thermal expansion

coefficient is used, the concrete matrix will be subject to much less strain when temperatures rise

and fall (Bamsforth 1984). Typically, aggregates with lower thermal coefficient values also have

a higher strain capacity (Table 3-2). Therefore, although it is much weaker in strength than

gravel or granite, using limestone may reduce the occurrence of micro cracks in mass concrete

due to it having a lower coefficient of thermal expansion and a higher tensile strain capacity.

3.4 Mechanical Effects of Temperature and Relative Humidity Gradients

Through experience and laboratory studies, many states have required that the temperature

differential does not exceed a certain value in mass concrete (See Survey of Specifications,

Chapter 2). After it has developed some stiffness, if the regions within are not moving (i.e.,

thermal movement) in unison with one another because of differences in temperature, the regions









act to resist the movement of one another. The tensile stress that concrete encounters as a result

of this is often referred to as restraint. Restraints may be classified as either internal or external

(Bamsforth 1984).

3.4.1 Internal Restraints

When the central region of a concrete pour is considerably hotter than the exterior regions,

its tendency is to resist the cooling shrinkage of the latter. Because there is a shrinkage gradient

that develops, cracking in the exterior region may occur as a result of this phenomenon,

increasing the exposure to ominous ions such as sulfates or chlorides. On the other hand, a

cooling core may cause internal cracks to form after it has hydrated, as a consequence of a

restraining outer shell (Houghton 1976, Mead 1963).

Internal restraints are characterized by the strains that occur due to opposing forces of

regions within a mass, as mentioned above. Although it is often overlooked by state

specifications, differential relative humidity may also be a cause for internal restraints (Grasely

2003, Bentz and Jenson 2004, Lee 2006, Ulm and Coussy 1995). Drying shrinkage may be one

result from the air having a low relative humidity, causing capillary tension to develop in the

pore structure (Bamsforth 1984, Grasely 2003, Ulm and Coussy 1995). Therefore, as a result of

both relative humidity and temperature being non-uniform throughout, differential movement

occurs, and depending on its degree may cause cracking. However, relative humidities are often

not monitored due to the humidity sensors either being unreliable or extremely expensive.

Work from Ulm and Coussy (1995) presented a theoretical and mathematical coupling of

both the effects from temperature and relative humidity. Some years later, Ulm and Coussy

(2001), worked to develop a finite element model, which was used to predict cracking based on

the unique concept of the hydration heat diffusion length (mentioned previously). Also, this work

and another publication, Faria et al. (2006), indicate that the heat production, flow of heat, and










flow of moisture may be treated independently from the mechanical movement. For example,

they assumed that the formation of a small crack would not effect the movement of heat or

moisture through the concrete. This assumption seems to be valid, when one is to consider the

size of these cracks (very small) in relation to the size of the concrete in question.

3.4.2 External Restraints

External restraints are those that may be imposed on mass concrete by its immediate

surrounding environment or an adj acent structure. Situations may involve ground rock imposing

restraint onto drilled shafts which undergo expansion or contraction throughout the hydration

process. Another example may involve a rigid foundation restricting the thermal movement of a

wall cast onto it. The magnitude of external restraint is directly related to the net amount of

expansion or contraction on a macroscopic scale, and the force that the surroundings impose in

order to prevent this expansion or contraction from occurring (Bamsforth 1984). In the study of

Pine Flat Dam (Figure 3-2), external restraints were a concern as layers (lifts) of the dam were

poured in increments of at least five days. The critical region of concern with external restraint is

usually the interface of the two bodies in question (Mead 1963). In this region, tensile and shear

stresses may cause cracking, especially in the newly poured concrete, where the maturity is not

as developed.

3.4.3 Temperature-Related Restraint

While internal restraints are usually governed by guidelines (maximum temperature

differentials) set by state specifications, external restraints are usually controlled by the

contractor' s experience in identifying subj ective issues. Internal restraints are usually of more

concern due to the frequency of cracks resulting from them and their associated complexity.

Therefore, one will find that the maj ority of literature written on mass concrete cracking has to

do with the internal restraints.










In general, three factors have been found to govern the uniformity of temperature within

concrete during its early ages, namely:

* Surface area to volume ratio
* Rate of hydration
* Amount of insulation used

The surface area to volume ratio has been found to raise concern when values are less than

1 ft '. This ratio is based on the same concept behind states defining mass concrete as having a

minimum dimension at or above a certain value. The concept is that concrete usually dissipates

most of its heat to the ambient air through its least dimension, and therefore the gradients and

maximum temperatures are usually controlled by this parameter. For a given mass structure, the

finalized design is given to the contractor, who usually becomes liable for its sound construction

with respect to material and dimension. Often times, contractors hire specialty engineers to

consult with them on the mix design and precautions to take (including formwork), in order to

produce a structure with as little cracking as possible.

By knowing the thermal expansion coefficient and hydrating temperature range, the

amount of rapid or slowly induced strain may be conservatively estimated with the use of the

thermal expansion equation (Houghton 1976, U.S. Army Corps 1997), namely,

e = a T (3-8)

However, Houghton' s early work (1976) conservatively assumed complete restraint of the

contracting system, and did not account for the effect that a gradient of expansion or contraction

had on the amount of strain encountered. This is similar to the Level 1 Analysis described by the

Army Corps (1997). The advantage of the finite element analyses (FEA) that were conducted in

the 90's and 2000's was that they more discretely accounted for stain gradients that developed in

mass concrete. Although FEA may be used to depict temperatures and stresses throughout mass









concrete in a detailed manner, some problems may be encountered. The problems included the

difficulty of predicting the mechanical or thermal properties as a function of the degree of

hydration, or maturity. Ultimately, this led to inaccuracy in the prediction of stresses.

Today, thermal stresses are usually obtained by FEA after determining the thermal

distribution, which may also be obtained by FEA. Nakamura et al. (1999) designed a finite

element model application to predict stresses that also accounted for the uncertainty in the

material properties and environmental conditions. Their study used a first-order approximation

theory based on Taylor expansion. De Schutter (2002) presented a study where he used his

previous work in order to devise an element simulation for temperature and stress prediction in

concrete. In his early work (De Shutter and Taerwe, Cem. Concr. Res., 1995), he developed a

general hydration model for both Portland cement and blast furnace slag cement. He also studied

the specific heat and thermal diffusivity of concrete (De Shutter and Taerwe, Mag. Concr. Res.,

1995) as a function of the degree of hydration. Another publication (De Shutter 1999) describes a

degree of hydration based Kelvin model for the basic creep of early age concrete. These studies

all contributed to the finite element model he developed, so that the 'uncertain' parameters

would be better justified.

Faria, et al (2006) developed a finite element program that accounted for the evolution of

the thermal conductivity and activation energy as a function of the degree of hydration. For this

application, the degree of hydration was computed as the ratio between the heat released up to a

certain instant, t, and the total heat expected. However, he made the assumption that specific heat

would remain a constant. This was based partly on De Schutter' s (Mag. Concr. Res., 1995)

study, where he found variations below 5% of its final value. He also assumed a constant value

for the thermal expansion coefficient.









Faria et. al (2006) also accounted for the evolution of the mechanical properties, including

compression, tension, and elastic modulus by the following equations (Rostasy et al. 2001):


L (a)= J o(3 -9)



a a)= (3-10)



Ec (a) = E, (3-11)


Another method of measuring thermal stresses (Kim, et al., 2002), shown in Figure 3-5,

involved something different from the recent FEM approach. Their study involved a frame

device which was built to restrain the thermo-mechanical movement of concrete. It was done by

building the frame to dilate according to constraint material which had a different coefficient of

thermal expansion when compared to that of concrete. An important feature of this method was

that the uncertain material properties of early age concrete such as the modulus of elasticity and

coefficient of thermal expansion could be calculated through innovative mathematical

relationships. This involved the stresses induced on the load cell as a result of the coupling

mechanism between the constraint material and concrete.

3.4.4 Relative Humidity-Related Restraint

With respect to its internal relative humidity, mass concrete may either undergo

autogenous or drying shrinkage. Faria (2006), indicates that Normal Strength Concrete (NSC) is

usually more susceptible to drying shrinkage while High Strength Concrete (HSC) is more

vulnerable to autogenous shrinkage. Faria also mentions that the affects which thermal gradients

have far outweigh the effects of autogenous shrinkage in NSC. In addition to this, problems

associated with drying shrinkage may simply be controlled by monitoring the relative humidity









and temperature of the exterior environment. For instance, Kim et al. (2002) ensured that the

testing environment for his device was kept at a relative humidity at over 85%, to minimize

drying shrinkage.

3.4.4.1 Autogenous shrinkage

Autogenously, concrete has a tendency to shrink due to the products of concrete having

less volume than the reactants (Bentz and Jenson 2004, Lee et al. 2006, Ulm and Coussy 1995).

Autogenous shrinkage occurs by the concrete consuming the internal moisture through the

chemical hydration process (i.e. developing small voids), and as a consequence creating capillary

tension through the menisci of moisture within the pore structure. However, much like thermal

movement, autogenous shrinkage does not occur uniformly throughout mass concrete, due to it

being dependant on the maturity, which is directly affected by the temperature (Ulm and Coussy

1995, Ballim 2003, Faria 2006). At later ages, the core region is prone to autogenous shrinkage

and may be restrained by the outer vicinity, which has undergone drying shrinkage at an earlier

age (Ballim 2003). As mentioned above, this becomes most significant when HSC is used.

3.4.4.2 Drying shrinkage

Concrete may undergo drying shrinkage when it loses water due to evaporation (at a

surface) to the ambient surrounding air. As Kim et al. (2002) mentions, higher tensile strengths

and elastic moduli are present in the interior portion of mass concrete at early ages due to there

being more maturity when compared to the exterior portion. Therefore, the surface may

prematurely undergo drying shrinkage as a result of capillary tension and in this case be more

vulnerable to cracking. Some authors, such as Ulm and Coussy (1995), mention that evaporation

may also lead to incomplete hydration of the exterior surface. Others (Mindess et al. 2003),

suggest that hydration may continue if water is later provided, however not to its full degree.









3.4.4.3 Combinational effects

With respect to both autogenous and drying effects, Equation 3-12 represents the capillary

tension with respect to relative humidity (Grasley 2003).



In(RH)RT
"caplllary. (3-12)


In this equation, RH is the relative humidity, and R, T, and Vm are the universal gas constant,

temperature, and molar volume of water, respectively. Conceptually, the equation describes how

the capillary tension is directly related to the evaporative potential of the water within the void

spaces to become vapor. This potential energy exerts what is known to be the capillary tension

within the micro-voids of concrete, and conceptually applies to both drying and autogenous

shrinkage. It can be seen in Figure 3-6 that theoretically, there is nearly a linear relationship

between capillary tension and internal relative humidity (Grasley 2003). The graph only shows a

relative humidity range between 50-100% because when the relative humidity drops below 50%,

the menisci are said to be unstable and other mechanisms are said to contribute to stresses.

In summary, when considering the mechanical stresses that develop in mass concrete, one

has to recognize both temperature and humidity differentials from the center to the exterior. As

mentioned earlier, drying shrinkage may be accounted for by providing a controlled

environment. Autogenous shrinkage may be assumed negligible in some circumstances using

NSC, but needs to be accounted for when using HSC.

3.5 Chemical Effects of Extreme Temperature and Relative Humidity

When considering the chemical alterations of hydrated paste, careful attention should be

made to individual temperature and humidity extremities that may alter the hydration products of

concrete. If certain regions within a mass structure have in fact endured through a rigorous










temperature cycle with minimal cracking due to internal and external restraint, have their

intrinsic properties been altered? Nasser and Lohtia (1971) found that the compressive strength

and modulus of elasticity are both affected immediately after the exposure to higher

temperatures. However, according to recent findings in the early 1990's, the most serious

consequences of higher curing temperatures are not always immediately evident in some

concretes.

3.5.1 Immediate Effects

Nasser and Lohtia (1971) conducted an experiment that consisted of two main test groups

of cylinders, Group A and B, which would be exposed to the same temperatures that included

35' F, 70' F (control), 160' F, 250' F, 300' F, 350' F, 400' F and 450' F. The only

difference between the groups is that they were to be exposed starting at a different time after the

cylinders were cast. Group A was exposed to these temperatures after one day of moist curing,

while Group B was exposed after 14 days of moist curing. Within group A and B, the cylinders

were divided up so that at least three would be exposed to a particular constant temperature for a

given time period, and then tested for ultimate strength and modulus of elasticity, immediately

after the exposure period. The specimens were all sealed so that no moisture loss would occur.

The effect which extreme temperatures have on compressive strength as an average

between groups A and B (groups mentioned above) is depicted in Figure 3-7. This plot

illustrates how the 14 days of moist curing of Group B created higher strengths than Group A

when exposed to elevated heat for less time, but the difference becomes less significant as you

approach longer heat exposure periods.

The overall difference in elasticity between Group A and B with respect to curing time is

depicted in Figure 3-8. Here it can be seen that at about 40 days of heat exposure the two

concrete groups were about equal in elasticity on average. Any exposure to heat for less than 40









days shows that on average there was a higher elastic modulus (less elastic strain for a given

load) for Group B. After 40 days, the contrary occurred as A had acquired a higher elastic

modulus (becoming more brittle), because it had been exposed to heat at an early stage in its

curing cycle.

In comparing the 4 and 14 day lines, with the 90 and 180 day lines, Figure 3-9 indicates a

critical temperature, where the magnitudes of compressive strength switch hands in both Group

A and B. The reason for this is in part due to the exothermic nature of the concrete curing

process. To a certain extent, the concrete matures quicker when exposed to higher temperatures

(see earlier discussion of Arrhenius relationship). However, when 250 F is exceeded, it can be

seen that the strengths for higher exposure periods drop dramatically. This occurs because altered

hydration reactions proliferate when the concrete exceeds temperatures of 250 F. Similar, but

more consistent trends can be illustrated in Figure 3-9 for Group B. The lines here are much

smoother due to less chaotic behaviors occurring at earlier maturities of heat exposure. Like

Group A, about the same critical temperature forces the lines to switch hands (in comparison of 4

and 14 day lines with the 90 and 180 day lines) indicating an environment which becomes too

hot to produce a higher strength product.

Looking at the elastic modulus versus curing temperature, Figure 3-10 indicates similar

trends noticeable between the relative magnitudes of the 14 and 28 day lines versus the 91 and

180 day lines when approaching a critical temperature of around 200-250 F. Although this

relative behavior stays consistent, the graphs depict that there is a notably more pronounced all

around decrease in the elastic modulus magnitude as the samples are subj ected to higher

temperature with a given age. The values of Em are indicated in some cases to decrease 50% or

more when exceeding temperatures of 350 F. Another unique trend when compared to strength









is that the elastic modulus increases with exposure time, given a temperature of 160 F. An

elastic modulus obtained at 70 'F nearly equals that of the samples exposed to 160 'F for 180

days.

Between the characteristics of strength and elasticity, Nasser and Lohtia's (1971)

experiment points to nearly identical properties arising in concrete when exposed to temperatures

of up to 160 F, when compared to 70 F, throughout the time of exposure from 0 to 180 days.

The assumption that such a temperature produces similar properties is of course only valid when

considering a specimen of uniform temperature while also being sealed against moisture loss, as

the experiment provided.

Summary of immediate effects. One of the conclusions drawn from Nasser and Lohtia' s

(1971) experiment was that as temperatures exceeded 180 F, highly crystallized co-dicalcium

silicate hydrate of weaker strength began to form. Mindess et al. (2003) also mentions this

occurrence. The critical temperature was essentially interpolated between 160 F and 250 F,

where the mechanical properties were affected the most. To get a closer look at the behavior, it

might have been advantageous to have tested the concrete at temperatures within the interpolated

region from 160 F to 250 F.

When conditions approached 320' F, more extreme affects may have been due to

hydrothermal reactions resulting in the transformation of the original tobermorite gel into new

equilibrium phases, of more crystalline and lime rich calcium silicate hydrates that have poorer

cementing properties (Nasser and Lohtia 2003). Delayed ettringite formation is another product

of high temperature exposure, but in this case it wasn't applicable due to ettringite only forming

after a substantial period of cooling (Mindess et al. 2003).










The precuring time proved a few interesting points as well. First of all, the early strength of

Group A was increased due to heat acting as an accelerator to the exothermic reactions. Second,

it seemed that this strength quickly diminished with increased time of exposure. Furthermore, as

noticeable in the temperature ranges from 250 F to 350 F, the results indicate that the longer

the curing time before exposure, the less deterioration occurred at extended ages. Therefore, the

hydration reactions of Group A were accelerated initially, but its strength was most rapidly lost

past 4 days. Group B may have been matured at a much slower initial rate but the strength loss

was not as much as A at extended ages.

3.5.2 Long Term Effects

Ettringite is a product of Portland cement hydration, which may be considered innocuous if

it forms when concrete is in its plastic phase (Mindess et al. 2003, Ramlochan et al. 2003,

Ramlochan et al 2004). It is produced when gypsum and tricalcium aluminate (components of

Portland cement clinker) are combined with water during the concrete's liquid phase:

C3A + 3CSH2 + 26H -C6AS3H32 (3-13)
Tricalcium Gypsum Water Ettringite
Aluminate


Once all of the sulfate ions from gypsum are consumed, the tricalcium aluminate proceeds to

react with the formed ettringite and water, in order to produce monosulfoaluminate:

2C3A + C6AS3H32 + 4H -,3C4ASH12 (3-14)
Tricalcium Ettringite Water Monosulfoaluminate
Aluminate


It has been found that delayed ettringite formation (DEF) occurs when concrete is first

exposed to temperatures above 160 F during curing, and then exposed to a well humidified

environment (Ramlochan et al. 2003, Ramlochan et al. 2004, Lee et al. 2005, Sahu and Thaulow

2004). The theory behind this is that at higher curing temperatures, a significant amount of









ettringite which normally forms during the hydration process of Portland cement, as seen in

Equation 3-14, is absorbed in the C-S-H or present in the pore solution (Sahu and Thaulow

2004). Ramlochan (2003) found that there was a considerable amount of ettringite crystallization

for OPC concrete at times between 100 and 360 days after exposure to temperatures above 160

F at the time of curing. This has been found to cause extensive damage, due to the delayed

growth of ettringite crystals having the ability to force cracks in the concrete by means of

wedging within hydrated cement paste (Ramlochan et al 2004).

The formation of ettringite is especially enhanced with the availability of sulfate, derived

from either internal or external sources. One internal source is said to be pyrite (FeS2) that

releases sulfate ions through its oxidation process (Lee et al. 2005). Exterior sources for sulfate

may include sulfur rich soils or deicer salts. Lee, et al. (2005) concluded that from petrographic

and scanning electron microscopy, combined with EDAX area element mapping, that DEF had

an important role in the cracking of several lowa highway concretes.

Sahu and Thaulow (2004) found that DEF forms as a result of curing temperatures being

below 1600F. Their study dealt with DEF in Swedish railroad ties, which were heat cured before

placement, and in service for seven years before visible map cracking was noticed. They

concluded that although the ties were steam-cured at 1400F, other factors such as high cement

content, high specific surface and high amounts of sulfate, magnesium oxide, and reactive ferrite

also contributed. They also warned that DEF may very easily form in the well-looking ties, if

moisture is absorbed. Petrographic examination, scanning electron microscopy, and energy

dispersive spectroscopy were all used in order to ascertain the nature of the cracking.

3.6 Measuring Mechanical Properties of Mass Concrete

Nakamura et al. (1999) mentions that the mechanical properties that are necessary in order

to predict the cracking of concrete involve the tensile strength and elastic modulus. However, it









has also been found important that creep be calculated as well. An additional parameter that

might be needed for future reference is autogenous shrinkage, although findings show it to be

negligible when compared to the magnitude of thermal expansion. In other words, a compilation

of these parameters (thermal properties discussed later) with respect to maturity time are needed

if one was to input them into an FEM.

Burg and Ost (1994) and Burg and Fiorato (1999) aimed at obtaining the thermal and

mechanical properties of regions within large massive concrete elements at different ages (not

maturities). Note that neither of these studies looked into the effects which thermal gradient

played on the strength, but only looked at the intrinsic properties developed as a function of real

time. These studies also concentrated more on compressive strength, rather than the tensile

strength of mass concrete.

In their first study, Burg and Ost (1994) cast 4 ft. cubed blocks in order to monitor the

temperature development. They then took cores from the blocks, in order to obtain the critical

properties, including compressive strength, modulus of elasticity, tensile strength, modulus of

rupture, thermal expansion, relative humidity, specific heat, thermal conductivity, and durability

properties. There was a lot of data collected in their study, but little conclusions were drawn from

the data by the researchers. However, the paper' s presentation of data in the form of graphs may

easily be interpreted as reference material by outside researchers.

Burg and Fiorato (1999) studied the use of high-strength concrete in massive foundation

elements. Their main concern was with regards to the heat generation and moisture lost during

hydration in HSC (see discussion on autogenous shrinkage, above), and how this would affect

the mechanical properties. The first step was to evaluate the temperature development within

massive caisson foundations. The next involved analyzing the 'in place' strength and stiffness by









taking cores at different radii from the center, and different depths from the top. He concluded

that the in place strength (derived from cores) was about 80% of the strength of the moist cured

cylinders. The elastic moduli were found to be 90% to 100% of the moist cured cylinders.

These conclusions seem to be consistent with findings from Nasser and Lohtia (1971),

where the strength and elastic moduli were not significantly effected by the temperature

exposures which were indicative of Burg and Fiorato' s (1999) study. Burg and Fiorato (1999)

indicated that temperatures reached about 1750F in the hottest regions. This temperature actually

coincides well with the critical temperature in Nasser and Lohtia's (1971) study, where the

concrete's mechanical properties just began to deteriorate when exposed for certain durations.

It is important to note that mass concrete cracks in tension and not in compression.

Therefore, it is important that an accurate tensile strength test be developed in order to predict

this occurrence. The following section discusses the research of tensile strength tests.

3.6.1 Tensile Strength

In the past, many approaches have been made in finding the tensile strength for concrete,

and researchers agree that obtaining this property may pose problems with respect to both

accuracy and consistency. Some methods are much more complex than others, especially those

associated with direct tension. Also, some test methods may be more compatible with concrete at

early ages.

3.6.1.1 Direct tensile tests

Direct tensile tests consist of applying a load which is theoretically perpendicular to crack

propagation. Although it has very little margin for error, many claim this to be the best way to go

about obtaining tensile strength, considering that it is done correctly. In this test, eccentricities

and other extraneous stresses need to be accounted for, so that the sample breaks in a predictable










region and on a failure plane relatively perpendicular to the axis of force. There are several ways

to go about doing this, including the following:

Gripping and notches. Elvery and Heroun (1968) presented an innovative method, where

a two-stage casting sequence took place. This included casting the specimens in a cylindrical

shape and subsequently casting an additional tapering ring of grout around the specimen ends, in

order to form an area where the specimens' tapers may act as a gripping wedge. They tested

tensile strengths at ages ranging from 1-28 days, with average 28 day strengths of about 270 psi.

The methodology was sound, and the data which was found seemed precise, but the lack of data

compilation made the study less convincing. Figure 3-11 displays a diagram of the specimen

design that they used.

Brooks and Neville (1977) described using samples similar to Elvery and Haroun (1968),

with bobbin-shaped ends. However, in their study they developed general power equation

relationships between the direct tensile strength and splitting tensile strength, modulus of rupture,

and compressive strength. The development of equations which relate these parameters have

become somewhat controversial, and especially with regards to the relationship between tensile

strength and compressive strength. They also found that the tensile strength of saturated

specimens increases at a slower rate than their compressive strength, with respect to age.

Al-Kubaisy and Young (1975) tested for tensile strength with the use of notches, cast in a

radial manner around each specimen. This was done in a similar two-step process as indicated by

Elvery and Haroun (1968). While the samples were being tested, by the direct longitudinal

application of force to the notches, ultrasonic pulse velocities were conducted through the

sample. In addition to this, strain distributions, and strain magnitudes were tracked as well. It

was found that 92% of the specimens broke within the region of uniform stress (the central part









of the specimen, between the notches) under a loading rate of 130 psi/minute. The average

tensile strength for this loading rate was 363 psi, with a coefficient of variation of 5.8%. The

diagram for this specimen may be seen in Figure 3-12.

Embedded bars. Several attempts have been made for this approach, with some

experiments having more precise results than others. It consists of having bars (usually steel) cast

within the test specimen, in order to apply an axial tensile force until failure occurs. Nianxiang

and Wenyan (1989) approached their experiment with the knowledge of possible slippage

occurring at the concrete-bar interface of larger specimens. They accounted for this by making

the central region of their large specimens less thick, so that the stresses would concentrate here

and hopefully create failure in this region. In Figure 3-13, it can be seen that they tested both

relatively large (bottom of figure) and small (top of figure) specimens.

The results showed tensile strengths of 175-290 psi with a coefficient of variation of 5-

15% for large specimens of different mixing proportions. For the smaller specimens, tensile

strengths were much higher at 275-450 psi and had a coefficient of variation of 7-14%. They

were loaded at a rate of about 30 psi/min. Ultimately, it was concluded that when comparing the

large specimens to the small ones, the test results seemed to agree with the following empirical

formula, which relates specimen size with tensile strength,

K, = 1- OO L~0.061oF)01 (3-15)

where Ks is the factor of the specimen size effect and F is the cross sectional area of the

specimen in cm2. Notice that when F = 100 cm2, Ks = 1.

Unlike Nianxiang and Wenyan (1989), Swaddiwudhipong et al. (2003) presented their

innovative method of accounting for slippage by using embedded bars that had claw-like grips

on the ends. Their results seemed very comprehensive due to the previous studies done by Wee









et al. (2000), where the claw-grip method was also introduced. They found that by using a two-

piece mould (Figure 3-14), they were able to assemble it easily and accurately, greatly

minimizing the eccentricity caused by the asymmetric axial loading encountered in many direct

tension applications. As a result, 100 out of 117 test specimens failed in the middle section, and

the standard of deviation of 12-18Cls for tensile strain capacity was significantly lower than those

of other tensile tests such as the flexure test.

Gluing. Gluing has been a popular approach to direct tension testing, and is the method

used in the CRD-C 166-92 standard. It consists of using the top and bottom faces of the

specimen for applying an epoxy bond to another surface (usually a steel platen) in order to apply

a longitudinal tensile force. Quian and Li (2001) analyzed the effects of metakaolin on the tensile

and compressive strength of concrete, using the gluing method for the tension specimens. Zhen-

hai and Xiu-qin (1987) also used this method, but had their aims on a depiction of a complete

stress-deformation curve for concrete. Reinhardt et al. (1986) was another publication, focusing

more on fracture theory and analysis, with respect to both static and cyclic loading.

One of the problems associated with gluing the specimen is that if one wishes to obtain

early age tensile strength (e.g. as is critical in mass concrete), it is difficult to provide a bond

with a wet interface of concrete. The concrete needs to be moist at early ages because it is still in

a critical maturing state, where desiccation would lead to an alteration in the apparent tensile

strength. There have been no papers cited, where early age tensile strength was tested by the

gluing approach.

3.6.1.2 Indirect tensile tests

Indirect tensile tests were developed with an understanding of the basic fracture mechanics

of concrete. These tests are based on calculating the resultant tensile stresses caused by forces









being applied on a parallel axis to the crack propagation. The indirect tension test (IDT) is the

method which is most preferred when compared to splitting tension, due to it tending towards

better accuracy and precision. However, the IDT may pose problems with respect to obtaining

the properties at early ages, due to sample preparation, including the cutting of specimens and

gluing of mounts for extensometers.

Indirect tension test (IDT). The IDT (Figure 3-15) is a test where a wafer-like sample

having a diameter of either 4 or 6 in. is cut from a cylindrical specimen at a thickness of 1.5 in.

Extensometers are subsequently mounted onto a circular face of the specimen, in order to obtain

strain on a two-dimensional plane. Originally developed for asphalt, it has recently been adapted

to accommodate concrete as well. Figure 3-15 is a depiction of an asphalt specimen, where the

only difference between the loading scheme of it and concrete would be the associated loading

and calculation software. The loading platens on the top and bottom exert a force onto the wafer,

which subsequently propagates a failure crack parallel to the axis of loading, and therefore

indirectly.

Splitting tension test. The splitting tension test, ASTM C496, involves the same concept

as the IDT, but it does not measure strain and may also be less consistent at depicting the tensile

strength. It consists of using a 4 x 8 in. cylinder where a load is applied transversely, in a similar

manner as the IDT. The tensile strain capacity may not be obtained from this test, but the tensile

strength is calculated by the following,



T = 2Pd (3-16)



where T is the splitting tensile strength, P is the maximum applied load, and I and d are the

length and diameter, respectively.









3.6.1.3 Hydro-static force induced tension tests

This type of test takes advantage of hydrostatic forces (Figure 3 -16), in order to induce an

axial tensile force onto the specimen. It may either involve the use of liquids or air, to give the

desired effect. This is accomplished by placing the concrete cylinder into an open-ended steel

jacket, where a fluid pressure is applied to the bare curved surface. It is generally accepted that

the indicated gas pressure at failure is the tensile strength of the concrete. One of the problems

related to this test is that there is little known about the induced stress that develops because of

the porous nature of the concrete. All that is known is that there are longitudinal stresses that

develop within, as a result of hydro-static stresses.

Mindess et al. (2005) carried out an experiment where he tested the difference between the

tensile strength of solid 4 x 8 in. cylinders vs. hollow 4 x 8 in. cylinders, placed into a steel

j acket. A diagram of the testing device is indicated in Figure 3 -16..

The data indicates clearly that there is negligible difference in the tensile strength between

hollow cylinders and solid cylinders, in the testing of two mix designs. Depending on the mix

design, the tensile strength for both solid and hollow cylinders was in the range of 4 MPa to 5.5

MPa (580 psi to 800 psi), with a standard of deviation of 0.275 to 0.375. The results agreed with

the theory that the gas pressure at failure is directly indicative of the tensile strength.

Clayton (1978) carried out experiments with the use of both nitrogen gas and liquid water

as the loading medium. His set-up was nearly identical to the one above. With the use of nitrogen

gas, he found that the indicated tensile strengths were much lower than that of water. However,

he mainly concentrated on the importance of the loading rate and how it affected the strengths

regardless of the loading medium. The results show that the quicker loading rates led to higher

tensile strength values.









3.6.1.4 Flexural test

The flexural strength is one measure of the tensile strength of concrete. Often referred to as

the modulus of rupture (MOR), the flexural strength may be measured by applying two point

loads to an unreinforced beam at 1/3 and 2/3 of the length. The dimensions of the beam should

be 6 x 6 in., with a length of at least three times the depth. The MOR is usually calculated using

ASTM C 78 (third point loading). ASTM C 293 notes the procedure of center point loading, but

is less conservative and may yield misleading strength values.

3.6.2 Tensile Strain and Elasticity

By having the ability to accurately measure tensile strain as a function of stress, this also

implies that an accurate estimation of the elastic modulus may be obtained from this data.

Although concrete's tensile stress-strain curve is not exactly linear in the first portion, a linear

assumption may be made, in order to classify the first phase of this curve as being elastic.

Swaddiwudhipong et al. (2003) utilized claw-like gripping and estimated the elastic

modulus in tension from the slope of the stress-strain curves (Figure 3-17). They also found that

in the linearly elastic regime (0 90% failure load) all values of the regression coefficient were

greater than 0.98. In this experiment, two electrical resistance strain gages were glued onto two

opposite side faces in the middle of the specimen.

The tensile strain capacity of concrete refers to the strain which induces a cracking failure.

The critical locations for cracking induced by thermal movement in mass concrete may occur

near the surface at early ages, especially where it is exposed to rapid drops in ambient

temperature and an accompaniment of drying shrinkage (Houghton 1976).

Early work done by Houghton (1976) depicts how the tensile strain capacity was obtained

from beam tests (Table 3-3). Notice that capacities for slow loading cases (creep) were included

also. In this situation, a coefficient for creep was to be factored into the calculations. The









modulus of rupture was used in this case to depict the tensile strength. The concrete was assumed

to be linear elastic until failure; hence the theory that the tensile strain capacity is equal to the

modulus of rupture divided by the elasticity. Another assumption that was made is that the

elasticity for the concrete under the bending test for modulus of rupture is equal to the modulus

of elasticity under a compressive load. The predicted strain capacities in this table represent

concretes mixed with Type II cement, moderate proportions of fly ash, air entrainment

admixture, and quartzite aggregate.

3.6.3 Creep

De Schutter (2002) proposed that compressive creep is valid when estimating thermal

restraint cracking. After finding the basic creep of concrete, De Schutter decided to predict the

mechanical behavior of hardening concrete by compiling the stiffnesses into a Kelvin chain

model, as shown in Figure 3-18.

In this model, Eco(r) is the young' s modulus as a function of the degree of reaction, fiel(r) is

the viscosity, and Ecl(r) is the spring stiffness. The degree of reaction, r, is simply the heat

produced thus far in the reaction, divided by the total expected heat of liberation.

De Schutter (1999) calculated compressive creep at early ages by using standard creep

frames, and found that loading the specimens to a value of 20% of the compressive strength at

the age of loading was ideal. In his experiments, he tested concretes of varying initial ages. He

began by loading the specimens to 20% and subsequently measuring initial creep strain (so), as

well as periodical creep strain. When the value for creep became relatively constant the final

creep strain was be measured (sEr), and the following calculation was made,


4 = 0 (3-17)

where cper is the final creep coefficient.









Faria (2006) also accounted for creep when using his FEM. Because of the large stress

fluctuations that occur in concrete during the early ages, the Double Power Law (DPL) was

implemented, due to it being reputable and one of the most widely used functions for describing

early age creep. This was used alongside a basic creep equation where a Taylor series expansion

was used to approximate the total creep in hardening concrete.

3.7 Measuring Thermal Properties

Although the main problem with predicting cracking seems to be the evolution of

strength and elasticity with respect to concrete's maturity, the thermal properties have also been

found to evolve. As was mentioned by Nakamura et al (1999), the thermal properties needed for

the prediction of thermal cracking in mass concrete include the coefficient of thermal expansion,

specific heat, thermal diffusivity, and the heat of cement hydration. Laplante and Boulay (1994)

reveal that there is an evolution of the CTE of up to about 16 hours of age. De Schutter and

Taerwe (Mag. Concr. Res., 1995) found that the specific heat decreased linearly with respect to

the degree of hydration. The values for thermal diffusivity and heat production were also both

found to vary to a significant extent, with respect to the maturity or degree of hydration.

3.7.1 Coefficient of Thermal Expansion

It has been disputed whether or not the coefficient of thermal expansion (CTE) evolves

with maturity to a considerable extent. De Schutter (2002) made an analysis for the prediction of

concrete cracking, assuming a constant value of CTE. However, Laplante and Boulay (1994) had

experimentally found that the concrete CTE decreased rapidly with increasing stiffness at early

age, and became relatively constant at about 16 hours. Beginning the tests at 8 hours, they



t Both maturity and the degree of hydration are used to express the amount of hydration which has taken place in
concrete. While the maturity has units in time (see Arrhenius, Eq. 6), the degree of hydration is expressed as a
decimal value, equal to the amount of heat liberated thus far divided by the total heat of liberation expected.









continued until 24 hours was reached, where they had found the CTE to be at an unmoving

value.

CRD-C 39-81 describes a test which may be used to find the linear thermal expansion of

concrete. This involves obtaining the length changes of the concrete as a function of temperature

change. It is very important that the accurate simulation of moisture is modeled for this

experiment, due to the CTE depending highly on the moisture content of the concrete. This may

be done by the immersion of the sample into water for at least a couple hours before the test. The

more aged the concrete is, the more the sample may need to be immersed, due to the need for re-

saturation of the pores. CRD-C 39-81 indicates a procedure for finding the CTE.

3.7.2 Specific Heat

The specific heat capacity of the paste may be experimentally calculated by the method

used from De Schutter and Taerwe (Mag. Concr. Res., 1995). This can be done by first

supplying a known energy quantity, E1, and measuring the corresponding temperature increase,

A61, without the addition of a cement paste sample to the heptane (see Figure 3-19). For a second

measurement, the cement paste sample is included and another energy supply, E2, 1S supplied and

the temperature increase, A62, iS TOCOrded. With the use of Equation 3-19, the specific heat, c,,

may be calculated,


cp = E E 8~;B~, (3-18)


where m, is the mass of the paste sample, E2 and E1 are the energy supplies with and without the

paste sample respectively, and A62 and 61 are the temperature rises with and without the paste

samples, respectively. Linear regression yielded the following equation, describing the specific

heat (c,) as a function of the degree of hydration (r) in cement paste.










c, (r) = 1300 x (1.5 0.5r) (J/kg K) (3-19)

Figure 3-19 shows a schematic view of the calorimeter which was used to calculate the

specific heat of the paste. Notice that it only has minor modifications when compared to that of

the calorimeter used for obtaining the thermal diffusivity.

3.7.3 Thermal Diffusivity

In the work by De Schutter and Taerwe (Mag. Concr. Res., 1995), the thermal diffusivity

was also calculated for young age concrete. Embedding a thermocouple within each specimen,

they measured the temperature at the center axis of the specimen vs. the time. The specimen, at

temperature 60 (200C), was subj ected to a water bath at temperature 60 + AO, which was 200C +

100C. The temperature 6(t) at the cylinder axis was then measured as a function of time. When

the following equation,


K~ 8, + AO B(t)~](-0


is plotted as a function of time, the curve becomes linear after some time, and the slope of this

curve is directly related to the thermal diffusivity. Linear regression of the results yielded the

following equation, where the degree of hydration was related to the thermal diffusivity.

a(r)= 4*10 x (1.10-0 10r) (m2/h) (3 -21)

Figure 3-20 depicts the calorimeter used for this test. Once again, it is very similar to the others,

with the only exception being that there is a thermocouple that is embedded within the cylinder.

3.7.4 Heat Production and Heat Production Rate

The heat generation Q was measured by Ballim (2003) with the use of a calorimeter. A

typical schematic of the calorimeter he used is presented in Figure 3 -21. The amount of heat

evolved from the sample was calculated from the following equation,










Q = mCpST


(3-22)


where m is the mass of fresh cement mixture, Cp is the specific heat capacity, and ST is the

change in temperature. With respect to the heat rate, the following equation was used, but only

under the unique conditions of the adiabatic test noted above.




Q', =(3-23)


3.8 Summary

Mass concrete may crack due to the thermal and relative humidity gradients that develop,

or may be weakened in strength by extreme temperatures or lack of moisture. The mechanical

properties that need to be quantified, in order to develop a finite element analysis include the

tensile strength, tensile strain, and modulus of elasticity. The thermal properties that need to be

modeled include the coefficient of thermal expansion, specific heat, thermal diffusivity, and heat

production.

Although the external environmental temperatures may come into play, the main concern

lies in the early age heats of hydration within mass concrete. Ballim (2003) created a two

dimensional finite difference model that effectively predicted the heats of hydration to within

two degrees celsius. In his theory he was able to get close to the actual temperatures by

accounting for maturity in the heat rate equation that he used. The maturity is an important

factor, because as a function of this, the heat production changes. He used the Arrhenius equation

to calculate the maturity of his test specimens.

In order to lessen these temperatures from the hydration reaction, several methods may be

used. This includes the use of mineral admixtures or by precooling the aggregates and water.









Another method to lessen the heat generation includes reducing the minimum dimension of the

pour so that heat may be liberated more readily.

Cracking occurs in mass concrete when the tensile strain capacity is exceeded. The causes

of this may include either internal or external restraint. While internal restraint is brought about

by strain gradients within the material, exterior restraint is brought about by externally applied

loads. While both may be the result of thermal expansion and/or moisture content, internal

restraints are brought about by the gradients in strain within the mass, and external restraints are

brought about by the average strain throughout the whole structure. In other words, the internal

restraints may be looked at as the structure fighting within itself, as external restraints are

brought about when an outside obstruction constricts the movement of the structure.

Another consequence that needs to be obviated for within mass concrete are the absolute

temperatures that develop. The immediate effects of extreme temperature includes the formation

of highly crystallized co-dicalcium silicate hydrate of weaker strength that may proliferate within

the concrete. This is said to especially come about when temperatures exceed 180 F (Mindess,

et al., 2003, Nasser and Lohtia, 1971). One of the long term consequences of extreme

temperatures is delayed ettringite formation, and especially becomes a problem when

temperatures exceed 160 F and moisture is present in the environment.

In order to obtain the tensile strength of concrete, several methods may be employed. The

main concern for these tests is the method that is used in order to apply the load, without

producing stress concentrations, or eccentric forces. The tensile tests include the use of

embedded bars, glued loading platens, pressure tension, indirect application of load, and beam

testing. All of these methods were studied so that one of them could be chosen for its application



































Table 3-1. Contribution of cement compounds to overall cement hydration (Mindess et al. 2003).
Amount of
Heat Heat
Compounds Common Name Reaction Rate Liberated Strength Liberation

Tricalcium
C3S Silicate Moderate Moderate High High

Low
Dicalcium
C2S Slow Low initially, Low
Silicate'
high later

Tricalcium
Aluminate and
C3A + CSH2 Gypsum Fast Very High Low Very High

C4AF + Ferrite Paste
CSH2 and Gypsum Moderate Moderate Low Moderate


to early age concrete, in order to calculate the strain capacity, strength, and elastic modulus of

concrete beams of different age.

It is disputed whether all of the thermal properties of concrete evolve with age. While

Laplante and Boulay (1994) claim that the coefficient of thermal expansion decreases up to 16

hours of age, others have assumed it to be constant in calculating thermal movement (De

Schutter, 2002). The specific heat and thermal diffusivity test used by De Schutter and Taerwe

(1995) was aimed at finding the evolution of these properties with respect to the degree of

hydration. They found that both the specific heat and thermal diffusivity decreases with respect

to the degree of hydration.












Table 3-2. Properties of typical course aggregates (Bamsforth 1984).
Aggregale rvl rnt Line- Llght-
typle stone weight
Thernilal
lexpansl on
coathicierit i0-s!"C 12.0 1008 0 7.0

Tensile
strain
capa~cty K10* 70 80 90 110

Lim~iling leaperglure
change in "C for
different restraint
factors:
i.B 7 16 16 20,
0.7i5 10 13 19 26
0.50 15 20 32 39
0.25 29 40 164 78

L[rniting
temperatures
d if ferential OC 201 28 39 55


Table 3-3. Estimation of tensile strain capacity (Houghton 1976).

Tenaile sftrin capacity Added tensile strain cap-acity Ulltimate
at age 90I days under from ereep under slow loadjng, tensile strain
raslrd Ledlng, age 5 to 90 days, capacity at 90dl
malaurnmillianths under slow loanding
Mdix miUjeaths
No.
Modulus of rupture ~ M en modulus of rupnture x
Modulus of elasticiy specific creep (1) +t (2)
(1) (2)
15071 290 4.1;5 x 19r = 70 2 t+219 i' 125
15122 I15i0170) s 5r FO 1* lus Lr IS% + $35) X 0,2;3* = 10521

1575 M $5- !1 -- 10 I = 45 ** NEl. (d St = jy 18)
15798 265 ;, 4.33 x 101-: = 41 5 IlL* + 671 u 2 = 59 1

,ated value baseda cm onum letb Teu5 o uhrae admxs













O~~LF 27I PLACED 01
-+-c--LIFT 26 PLACED



35
****** ""*56 LIFT JO IN T 27
r~70 7e 626


so 350 3'-6" ,6

so~~35 4 IF JtN 2


46'2 LOCATION DETAIL


I 0 22 24 26 ) 50 I 5
MARCH APRIL 1951


Figure 3-1. Vertical temperature gradients vs. time, within a dam lift (Mead 1963).





PLACING INTERVAOL IN DAYS



1 *4'1~~CONCRETE TEMPERATURcES



%M~I I I r h241] -- EL.5u84

I ~31 EL. ""578


22 e EL.572TI

4017.L EL.566

I NEAN DAILY TEMPERATURE OF AIR LO~~

0O 20 51 i0 20 21 D 20
JANlUARY FEBRUARYV MARCH 1954


Figure 3-2. Vertical temperature gradients vs. time, between several lifts (Mead 1963).













































I l I I I
0 2 4 (1 8 10 12 1
Temperatulre rise "C per 100 kg cementitious content

Figure 3-4. Effect of minimum dimension and replacement % of BFS on temperature rise
(Bamsforth 1984).


Milliml.J jillef ulU 111

5a Rly ash





2 Replacemnent %


1 -


0 2 4 6 8 10 12 14
Temperature rise "O per 100 kg cenientitious content

Figure 3-3. Effect of minimum dimension and replacement % of fly ash on temperature rise
(Bamsforth 1984).


Mininjmur dimensio6n rn

5b Blastiurnace slsepaga~l ZI
































80 40! 120 E1 log1 1201 2 40 80
m 8



Figure 3-5. Thermal constraint device (Kim et al. 2002).






50[



3 0


Consr~aint material
s~aeluminum or Iny r
7 ~~~ i load cell !-T----


concrete


70 80
Internal Re at ve Humidity (%)


90 100


Figure 3-6. Effect of internal relative humidity on capillary tension (Grasley 2003).


Unirt : mm






































1 4 8 14 28 56 90 180

TIME IN DAYS


Figure 3-7. Compressive strength vs. time of heat exposure (Nasser and Lohtia 1971).


5000
(35L5)1


CONCRETE B


2000




g: 1000
(L (710.3)


i CONCRETE A E
o o


LEGEND
SYMBOL
o


SERIES
CONCRETE A\
CONCRE TE B


1200




1000


CONCRETE 8-






CON(CRETE A


O
o
o


600 t-


LEGEND
SYMBOL SERIES
o CONCRETE A
CONCRETEE B


14 28


56 100 180


TIME IN DAYS ( LOG SCALE )


Figure 3-8. Elastic strain vs. time of heat exposure(Nasser and Lohtia 1971).









































l i s l i i l i t i


..4





CONCRETE A


6000 I


4000
(5281.2)

2000
rt4o.s)


0 515 70 100


(71) (93.5) ()21) (149) (177) (209) (232) *C

10200 250 500 350 4100 4M0

SYMBOL AGE IN2 DAYS
-2.".------ra-


..----c- -
5

r--.-


8000


4000

2000.p

04oos)


(4 7) (21.4) (30)


(1T) (93.d) (124) (149) (177) (205)1 (232) Ce


0 36 70 100


160 200 21)0 300 550 KI 40040
TEMPERATURE *F


Figure 3-9. Graphs depicting compressive strength for concrete subj ect to high temperature
(Nasser and Lohtia 1971).


6
(42.)8)





(21.09)
2
(14.06)

(7.03)


CONCRETE A


(17)r (2,.4) (38)


(71) (935) (121) (149) (177) (205) (232) C
I I r I III
160 200 250 300 350 400 450


O 35 70 100


LEGEND


6
(42 18)

(35.(5)
4
(28.12)
3
(21.09)
2
(14.os)

(7.03)


SYMBOL
-------- -4-. -- -






NhCRETE B --


AGE IN DAYS
14


(71) (95.5) (121) (149) (I17) (205) (232) *C

160 200 250 300 350 400 450


O
(17) (21.4) (58)


CC


0 35 70 100


CONYCRETE 8


TEMPERATURE *F


Figure 3-10. Graphs depicting the elastic modulus for concrete subj ect to high temperature

(Nasser and Lohtia 1971).










12 00


0125 00 f tUUv












Figure 3-11. Elvery and Haroun (1968) concrete tension specimen (dimensions in inches).










90R 00




380






Figure 3-12. Concrete specimen with notches (Al-Kubaisy and Young 1975).











150 ~
18


550 ~mt
1 550~ i


mnr dlam. bar

I~I
--'lljC7 mm


Figure 3-13. Nianxiang and Wenyan (1989) large and small specimens.


Figure 3-14. Swaddiwudhipong et al. (2003) used a simple two-piece mould, with claw-like
embedments.












































































O 20 40 650 80I 100a 12 140 16018
Tensite! Strain Ecrl


Figure 3-15. The IDT test, with a sample of asphalt concrete.





D=100mm Concrete cylinder
End rng / Socket head bolt


Steel Jacket


30~ ~trogen gas inlet 82 3Z




Rubb~er "O" rng


Figure 3-16. Sectional view of the nitrogen gas test, with a diagram of principle stresses
(Mindess et al. 2003).


9.%

3;


~ 2.5



~E~ 1,5

or
~ I

CI.S

D


Figure 3-17. Typical stress-strain curves for concrete in tension (Swaddiwudhipong et al. 2003).























Figure 3-18. Kelvin chain model (De Schutter 2002).






Chr onomtet
d Motor


Pr inter
Thermocouple








Figure 3-19. Schematic drawing of a calorimeter used to measure specific heat (De Schutter and
Taerwe 1995).


rid (r)











Chrononeter


Thermocouple

Cemen-t Poste


Figure 3-20. Schematic drawing of a calorimeter used to measure thermal diffusivity.


Figre -21 Scemaic rawng f acalrimteruse tomeaurethehea ofcemnt ydrtio
(Balli 2003)









CHAPTER 4
FLEXURAL TEST FOR EARLY AGE CONCRETE

4.1 Background

4.1.1 Early-Age Concrete

One of the challenges with this proj ect was to determine a way in which the stress and

strain behavior could be measured in early age concrete. In this case, "early age concrete"

pertained to samples which were from one day to seven days old. Beam tests were determined to

work fine, so as long as the strain gages were well bonded to the concrete. As early age concrete

was of concern, the adhesive had to be compatible with a wet concrete surface. The preferable

properties characterized by Loctite 454 surface gel were fitting for this purpose, due to it readily

reacting with moisture, in order to form a bonding interface.

4.1.2 Third-Point Loading Scheme

To obtain the tensile strength and strain of this concrete, it was decided that beam tests

would be used. Commonly known as third-point loading, ASTM C78 describes a method which

utilizes a support on each end of the beam, and point loads located at 1/3 and 2/3 of the span. The

dimensions of the beam should include a 6"x6" cross section as well as a length of at least three

times the depth. It is indicated in ASTM C78 that a load rate of 30 lbs/sec is fast enough to not

induce significant creep, and slow enough so that premature rupture does not occur. This loading

rate is applied until the beam fails, and subsequently the stresses in the extreme fibers may be

calculated by Bernoulli's Theorem. The maximum stress incurred onto the beam is called the

modulus of rupture (MOR). Figure 4-1 shows the stress and strain distribution, according to

Bernoulli's theorem.

Another method of measuring the MOR is described in ASTM C293 as the center-point

loading test. Unlike the third-point loading scheme, this tends to create sporadic results due to










the moment peaking at the center point, as opposed to it being constant throughout the middle

third of the beam. By using the third-point test, the researcher was able to confidently place the

strain gage in the middle of the constant stress region so that the stress-strain data could be

procured. The compressive elastic modulus of the beam was then compared to compression

cylinder tests where extensometers were used to measure the deformation. These cylinders were

also broken, in order to compare the empirical relationship between crushing strength and elastic

modulus with that of the compression region of the beam.

4.1.3 Compression Test for Elastic Modulus

The standard test procedures of ASTM C39 and C469 were generally followed in running

the compressive strength and elastic modulus test. Figure 4-3 shows the set-up for this test,

where 4 in x 8 in cylindrical specimens were used. The two ends of the specimen were ground

evenly before testing to insure even loading during the test. Two 4-inch extensometer

displacement gages, which were held by four springs, were mounted on the sides of the

specimen. The specimen was then placed in a compression testing machine. The testing

machine used was hydraulic-controlled and had a maximum capacity of 220 kips. Load was

applied to the specimen at a constant loading rate of 26 kip/minute until failure. The outputs

from the displacement gages and the load cell from the testing machine were connected to a data

acquisition system, which records the data during the test. The average displacement reading

was used to calculate the strain, and the reading from the load cell was used to calculate the

stress.

4.2 Flexural Test Materials

4.2.1 Instrumentation

* Strain Gages Tokyo Sokki Kenkyuj o Co., Ltd., Type PL-60-1 1-3LT
* Loading Frame Instron 3384, with third-point loading attachments
* Signal Conditioning Unit National Instruments SCXI 1000










* Two Computers One for strain, and the other for load cell acquisition

4.2.2 Sample Accessories

* 6x6x22" Beam Moulds
* Concrete Ingredients Per ASTM specification (see Results and Discussion)
* Drum or Shear Concrete Mixing Device
* Vibration Table
* Mineral Oil
* Plastic Cover for Beams


4.2.3 Preparation Accessories

* Glue Loctite 454 surface gel
* Non-Bonding Polymer Sheath Packaged with strain gages
* Rubber Setting '/" thickness, 5" long
* 2x4" Block 5" long
* Cloth Clean and damp
* Acetone Standard concentration
* Sand Paper Fine Grit
* Masking Tape
* 18" Ruler
4.3 Flexural Test Procedure

4.3.1 Casting

1. Wipe the forms with mineral oil, so as to produce a non-stick surface

2. Mix batch of concrete per ASTM C192

3. Procure slump, unit weight, and any plastic properties of concern

4. Place concrete into the beam molds so that '/ of the volume is filled

5. Vibrate the half-filled molds for 12 seconds on a vibration table

6. Fill the molds to the top with concrete and vibrate for 12 seconds

7. Trowel the top surface of the concrete, using a wet instrument

8. Cover the filled molds with a plastic cover, so that negligible moisture evaporates from the
surface.










4.3.2 Sample Preparation and Storage


1. De-mold after 24 hours and either begin to prepare the samples for one day testing, or store
the samples in a lime bath solution for later age testing.

2. Procure specimen of desired age and let it sit on the counter top for 30 minutes for moderate
evaporation.

3. Sand the central region of the top and bottom faces of the beams, approximately a 2x5"
surface area. Note that the top and bottom faces should be the original side faces of the
molded specimen. This allows for smooth surfaces to be used, as opposed to the trowelled
surface.

4. Wipe away the concrete dust with a dampened cloth. Then, proceed to wipe the sanded
region with an acetone-dampened cloth. Do this for both faces.

5. Draw a line along the width at each of the 1/3 portions as well as the mid-point of the
specimen. Draw another line along the length in the center of the specimen. Do this for both
faces.

6. After acetone has apparently evaporated, place a pencil-lead-thick line of glue onto the strain
gage, and carefully center it onto one of the marked faces of the specimen.

7. Carefully place the polymer sheath onto the top of the gage and work a finger over it lightly
to encourage bonding.

8. Carefully place the rubber setting and then the 2x4" block onto the top of the sheath and
press firmly for approximately 5 minutes.

9. Repeat 14-16 for the other face.

10. Gently secure the wires in the area where they connect to the gage by taping them down in
this region. This will prevent the fine-gauged wires from tearing. Do this for both gages.

4.3.3 Testing

1. Carefully center the beam onto the loading frame, so that the 1/3 marks accurately align with
the loading platens. Note: Ensure that the strain gage wires will not be crimped by the
loading action of the test frame!

2. Connect both gages to the SCXI-1000 unit, ensuring proper quarter bridge configuration

3. Run the loading apparatus at a rate of 30 lbs/sec, acquiring both voltage data (from strain
gages) and the load cell data.

4.3.4 Data Analysis

1. Determine Vr, from the voltage output data with the following equation,











Ve (4-1)

where Vx is the variable voltage; Vi is the initial voltage, and Ve is the excitation voltage.

2. Determine the strain from the following equation,

4 Vr

GFl(1 + 2Vr) (4-2)

where GF is the gage factor.

3. Determine the stress, from the load output data with the following two equations,


I=" (4-3)




Where P is the load cell readings; L is the span length (not the beam length); c is V/2 the depth;
and I is the moment of inertia of the section.

4. Correlate the output values so that they match to one another. Do this by observing when the
strain voltages begin to increase. Lastly, check the failure stress and strain to ensure that they
are terminating at approximately the same value.

5. The mechanical properties shall be calculated in the following manner:

* Tensile Strength the peak tensile stress before the beam breaks.
* Tensile Strain Capacity the peak tensile strain before the beam breaks.
* Elastic Modulus of Tenison See Equation 4-5.
Et=ft40 ft20
8740 20d (4-5)

Where ft and et is the stress and strain at the given percent of strength and capacity,
respectively.

* Elastic Modulus of Compression See Equation 4-6.
Ec = fc0 2
FC40 20C, (4-6)

6. A good way to compare the elastic modulus of compression with another experimental
method is by doing modulus of elasticity tests on 4x8" cylinders, with mounted strain
extensometers, as was done in our research proj ect.









4.4 Results and Discussion

Concrete used contained fine aggregate with a fineness modulus of2.5 and coarse

limestone aggregate with a maximum size of %/". The cement which was used was Quikrete

Type I/II Portland cement. In addition to these ingredients, water reducing admixture was added

(WRA 64) to make the concrete more workable. Overall, the mix seemed to be quite wet, and as

a result it had a higher slump of 10 inches. Tables 4-1 and 4-2 give a summary of the materials

used.

The main objectives of this mix included quantitatively and qualitatively observing the

strain gage results and assessing the feasibility in attaching them to the early age concrete.

Another goal was to observe the evolution of the early age tensile strain capacity, elastic

modulus, and tensile strength for one and three day specimens. It was observed that by following

the procedure outlined above, there was no apparent problems in attaching the gages, nor was

there any qualitative problems observed during the loading period. The numerical data yielded a

steady and relatively linear progression of strain as the beams were loaded at 30 lbs/sec (Figure

4-5 and 4-6). Although there was no noticeable discontinuity in the stress versus strain

relationship for either compression or tension, the results seemed to imply that the compressive

elastic modulus was more reliable than the tensile elastic modulus.

Figure 4-4 graphically depicts the comparison of different methods used to calculate the

elastic modulus in compression. For the three-day samples, the elastic modulus for the

compression region in the beam (3771 ksi) almost identically matched the empirical predictions

for the elastic modulus (3745 ksi). The empirical relationship was obtained by breaking cylinders

(by compression) in order to get their strength, and using it in the equation obtained in ACI

8.5.1-2002 (Equation 4-7).










Ec = 57000 ~c


(4-7)


Another value for the elastic modulus in compression was obtained for the 3-day samples

with the use of extensometers that were attached to 4"x8" compression cylinders, and the

average (3928 ksi) compared fairly well with the empirical average (Table 4-3).

The MOR and elastic modulus both displayed consistent results with age (Table 4-4). As

expected, the concrete became stiffer and stronger with age. Regarding the tensile strength, the

average MOR at one-day (0.457 ksi) displayed an expectable evolution towards the three-day

MOR (0.494 ksi). The elastic modulus displayed more change than strength did when comparing

1-day (2868 ksi) with 3-day (3377 ksi) beams. This is due to there being less tensile strain with

respect to stress.

One of the issues with the results was that the elastic modulus in tension did not match that

of the compression elastic modulus. The Bernoulli Theorem assumes that the neutral axis is

located in the center of the beam, and that there is a linear distribution of stress and strain. The

flexural test that is used in our study for early age concrete is therefore partly discredited due to

the compressive and tensile elastic moduli not matching to one another. This is due to the tension

region undergoing micro-cracking and plastic deformation before the ultimate failure occurs.

When comparing these results to literature findings, it seems that the change in these

properties with respect to age displays proportionate trends in behavior, but only display

magnitude consistency within the testing method and not as much between other methods

employed. For example, the direct tension test used by Swaddiwudhipong et al. (2003) produced

strength values that were less than those obtained by the MOR tests in this research. It is believed

that the direct tension test produces less strength due to the eccentricities that can result from a

slight miss-alignment of the applied load. Due to the constant region of stress produced in the









third-point beam tests (Figure 4-2), it is believed that there is a greater tendency to produce

results that are more representative of the true properties.

The tensile strain capacities for the beam tests were very consistent with respect to one

another (Table 4-5), therefore producing a very low standard of deviation. This was due to the

concrete consistently rupturing at a similar tensile strain at a given age. The one-day concrete

had an average tensile strain capacity of 183Cls while the three-day samples had and average of

159Cls. This holds consistent with the fact that the stiffness (E tension) increased considerably,

between one and three days.

4.5 Summary and Conclusions

The results of the beam tests using surface-mounted strain gages show that it is feasible to

run this test on early age concrete. Consistent stress-strain plots can be obtained from this test.

The measured tensile strength and elastic modulus (tension and compression) increased and the

tensile strain capacity decreased with age from one day to three days. Although the use of Loctite

454 surface adhesive created an adequate bond at the concrete-gage interface, it is evident that

the tension region of the beam behaved differently than the compression region.

The compressive elastic modulus obtained from the beam test compared well to the

estimated elastic modulus from compressive strength using the ACI equation (Equation 4-7), and

the measured elastic modulus from compression cylinders. However, the tensile elastic moduli

were generally lower than the elastic moduli in compression. This is thought to be due to micro-

cracking within the tension region at an early stage in the loading process. Due to this occurring,

the stress versus strain curve appears to be flatter, and therefore produces a lower modulus. The

observed difference between the measured strains in the tensile zone versus the compressive

zone warrants further investigation into this area.










Table 4-1. Material weights used.
%/" Aggregate Water WRA 64
W/C Ratio F. Aggregate (lb) (lb) Cement (lb) (lb) (ml)
0.45 123.45 204.96 88.80 45.59 100.00


Table 4-2. Mix proportions used, according to PCA recommendations.
F. Aggregate Cement
W/C Ratio (lb/cuy) %/" Aggregate (lb/cuy) (lb/cuy) Water (lb/cuy)
0.45 1040 1800 755 340


Table 4-3. Mechanical properties for three day aged cylinders.
Ecomp,
Extensometer Ecomp,Empirical
Sample # Age (Day) (ksi) (ksi)
1 3 3727.9 3886.7

2 3 4098.7 3819.5

3 3 3958.5 3529.7

AVERAGE 3 3928.4 3745.3


Table 4-4. Mechanical properties for the beam.
Age Ecomp Beam
Sample # (Day) MOR (ksi) (ksi)

1 1 0.474 2901.9

2 1 0.438 3420.2

3 1 0.457 3550.9

AVERAGE 1 0.457 3291.0

4 3 0.489 3371.3

5 3 0.552 4106.1

6 3 0.440 3835.5

AVERAGE 3 0.494 3770.9


Et Capacity
(cls)

184

184

181

183

159

159

159

159


Eten Beam (ksi)

2901.3

2778.3

2923.8

2867.8

3611.5

3323.4

3195.7

3376.9












3-Day Cylinder

NA

187.226


189.704

NA

NA


Table 4-5. Standard deviation for various tests and ages.
1-Day
Sample Type Beam 3-Day Beam

MOR (ksi) 0.018 0.056

Ecomp (ksi) 343.257 371.603

Ecomp Empirical
(ksi) NA NA

Eten (ksi) 78.286 212.987

st Capacity (us) 1.732 0.000


Bemn CrosSctim ~ StanSrss



Figure 4-1. Theoretical stress and strain distribution through cross section





















Lrl I Lil i ULl


M= PL.6


Figure 4-2. Loading scheme and moment diagram.


Figure 4-3. Loading scheme for the measurement of elastic modulus in compression, with the use
of extensometers.























4500.0




4000.0







-5


3000.0




2500.0




2000.0




1500.0




1000.0




500.0




0.0


-




-




-




-




-




-





.


-




-




-




-




-




-




- -


WEcomp Beam

IEcomp. C., (e:.tnsorrater)


1 2 3








Figure 4-4. Comparison of methods used to obtain compression elastic modulus for concrete.

This plot depicts three day samples.
















































-0.0002 -0.00015 -00001 -0D0005





Figure 4-5. Typical plot of 1-day stress


0 0D0005 00001 0D0015 0.0002
Strain


-*Top Strain
-8- Bot Strain
















































-0.032 -0.m015 -0DU1 -0.KOO5


0 0.COU5 0.ao1 0.m015 0092
Strain


Figure 4-6. Typical plot of 3-day stress


--Top Strain
-aBot Strain









CHAPTER 5
SPECIFIC HEAT FOR EARLY AGE CONCRETE AND ITS COMPONENTS

5.1 Background

The specific heat of concrete (c) is an essential property, because it can be directly used to

calculate the temperature increase of a material with known mass, when given the amount of

thermal energy supplied. The following equation depicts how the specific heat may be calculated

experimentally,


c = (5-1)
mx ST

where E is the applied thermal energy (kJ), m is the mass of the material (kg), and 6T is the

change in temperature of the material (oC).

The specific heat is also related to the thermal conductivity in the following way,


c = (5-2)
ap

where AZ is the thermal conductivity of the material, a is the thermal diffusivity, and p is the

density.

With respect to mass concrete, the thermal energy that is of main concern is that of the

hydration reaction of the cementitious materials. When the specific heat is used as a modeling

parameter alongside other properties including thermal diffusivity, coefficient of thermal

expansion, and heat generation, one is able to model the temperature rise and expansion of a

concrete mass.

Customarily, a differential scanning calorimeter (DSC) is used to obtain the specific heat

of materials (ASTM E 1269-05). However, the problem with applying this test to concrete is that

because the required sample amount is very small (a few milligrams), it would not be

representative of the concrete as a whole. Also, it was desired that a more simple procedure









could be developed (than that compared with the DSC procedures) and where less expensive

equipment would be needed. The goal of this research was to therefore use larger samples that

would be tested by precise, yet more simple procedures.

The specific heat tests used in this research involved the use of a calorimeter fabricated by

the researcher, in accordance with De Schutter and Taerwe, 1995, and another calorimeter

designed and fabricated by the researcher. The first experiment (De Schutter and Taerwe, 1995)

involves the use of two baths, with an interior one of oil and an exterior one of polypropylene

glycol. The liquids used in these baths were chosen due to their ability to rapidly transfer heat. In

the interior bath, a stir paddle, heater, and two thermocouples were placed within. The exterior

bath was of the circulatory type, and regulated a constant temperature at approximately that of

the room (Figure 5-1).

The procedure involves supplying a known flux of heat energy into the interior bath and

analyzing the resulting rise in temperature within The stir paddle was used to distribute the heat

evenly throughout the interior bath. In the first step, a known quantity of heat is provided to the

interior bath without the concrete sample (AE 1), and the resultant temperature rise (A61) of the

oil bath is measured. Following this, the concrete is added to the oil bath and another quantity of

energy is supplied (AE2) and the change in temperature of the concrete (A62) is measured. In this

case, the change in concrete temperature may be measured without the embedment of a

thermocouple by extrapolating from the temperature vs. time plot for the interior bath (Figure 5-

2). In order to measure the heat energy of both cases, a watt meter was used that was able to plot

watts as a function of time. With this plot, the energy could be obtained by taking the area under

the curve.










The region of the graph (Figure 5-2) where the temperature peaks (above the value A62)

represents the process of the concrete establishing thermal equilibrium with the oil. After this

peak has resided and linearity is achieved, the linear portion of the graph can be extrapolated to

obtain A62. Once this is calculated, Equation 5-3 may be used to determine the specific heat of

concrete. The researcher noticed that when adapting De Schutter's experiment, there wasn't as

pronounced of a peak as was indicated in the literature's graph. However, there was a nonlinear

and a linear transient state that was noticed after the heater was shut off.

I fAE2 AEl\
c = (5-3)
me \AO2 All1

The calorimeter that was designed by the researcher was based on a different concept than

De Schutter' s experiment. The scheme was to have a fully insulated flask, in order to contain all

of the heat energy input. In this case, there was a negligible transient state after the heater was

shut off. This experiment also utilized two thermocouples, that were used to indicate any thermal

gradient that was present within the calorimeter, as shown in Figure 5-3. The researcher chose to

do this in order to stress the importance of establishing thermal equilibrium.

Although the concept was different, the procedures between the two approaches were very

similar. For the insulated test, there was also a run with and without material. The specific heat

was also calculated in a similar manner, except for the AT2 term being measured directly (from

thermal equilibrium), as opposed to extrapolation.

5.2 Insulated Flask Test

5.2.1 Calorimeter Accessories

* Dewar flask 4000ml capacity
* Heat transfer oil Duratherm 600, heat transfer fluid
* Heater Gaumer, 500 Watt, with screw plug
* Air motor With a drill chuck attachment










* Stir paddle Powered by air motor and fitting into chuck fitting
* Wooden Mount Used to cover the top of the flask and to mount accessories
* Material Specimen 100 250 grams of material, per Table 5-1.


5.2.2 Data Instrumentation

* Data Acquisition Daq PRO, 5300
* Watt Meter Watts Up Pro, Power Analyzer
* Thermistor Needed to verify temperatures
* Thermocouple Three type J
* Scale Accurate to 0.1 gram


5.2.3 Cast Procedure

1. Cast 4 in by 8 in cylindrical specimens with caps to seal moisture.

2. De-mold the cylinders at 24hrs +/- 1hr.

3. Place the cylinders into a lime bath solution to provide a neutral curing environment for
the concrete. Withdraw them at necessary ages for testing.

5.2.4 Test Procedure Calibration

1. Ensure that the Daq Lab is configured properly. This includes the following menus:
"System Configuration" ensure that input filter is on, that no average is taken, and that
temperature is in C.

2. "Setup the Logger" Ensure that the three inputs used are set to read as type J
thermocouples. Also be sure that the rate is set to every second for 5,000 samples.

3. Warm up the data acquisition system for the thermocouples by turning it on and having it
read temperatures.

4. Ensure that the accessories are put into position on the wooden mount. Orient the
thermocouples so that one touches the bottom surface of the flask, and the other is in the
center. Keep all of the accessories in the same positions for each run. Also, place one of
the three thermocouples outside of the beaker to read the air temperature.

5. Zero the dewar flask (without the mount), and leave it on the scale.

6. Check to ensure that the heat transfer oil is equal to the room temperature. This may
require leaving the oil in the room for 24 hours before testing.

7. Add oil to the flask, so that a two inch lip is left between the level of the oil and the top
edge. Record the mass of the oil.









8. Place the flask into position underneath the air motor apparatus and put the wooden cover
on the flask with the paddle, heater, and thermocouples placed into position. Fit the stir
paddle into the chuck fitting on the air motor, and ensure that it vertically passes through
the center of the stir paddle hole on the mount.

9. Start the stir paddle. Adjust the regulator so that there is a 6 psi driving pressure.

10. Ensure that there is close to zero thermal gradient within the flask. This is done by
observing the deep and middle thermocouple temperatures as the stir paddle turns. Also,
check that the temperature in the room is approximately equal to the temperatures within
the flask.

11. Turn off the data acquisition system after a final check of the internal flask gradients, and
any differential between the room and flask.

12. Begin experimentation by simultaneously initiating the readings for the thermocouples,
starting the heater (obtaining power measurements) and starting a timer. It needs to be
made certain that both systems are synchronized, so that the power measurement
coincides with the temperature measurement. This may take some trial running by the
researcher to check the time when the Daq Lab initiates its inputs. It does not occur the
moment that the "start logging" option is initiated.

13. Leave heater running for four minutes.

14. Unplug the heater from the watt meter at exactly four minutes, leaving the Daq Lab to
continue making measurements.. After this, unplug the watt meter from the power outlet.
For the Watts Up PRO, the data will be saved to system, even though the meter was
abruptly unplugged from the wall. Note: The Watts Up PRO will begin to generate two
second intervals between readings if the meter is left plugged in for more than 17 minutes.
Therefore, the meter should be unplugged immediately after heating so that one second
intervals will be obtained to coincide with temperature readings.

15. Continue to obtain temperature readings for thermocouples for a duration of time in
accordance with Table 5-1. The duration of the calibration run depends on the duration of
the type of material tested in the materials test. Even though the calibration run does not
include material, it needs to be run for the same time period as the material run.

16. After this time period has elapsed, press the escape button on the acquisition system to
end the logging.

17. Stop the stirrer, remove it from the chuck and remove the wooden mount (with all
components) from the flask. Set it, along with its mounted components onto a paper towel.
Wipe off any oil on the heater, stir paddle, and thermocouples.

18. Pour the oil from the flask into a 6"xl2" cylinder mould, place a cover on it, and label the
calibrated fluid.










19. Place the fluid into a refrigerator for about an hour to bring the temperature back down to
the room's value. Check to ensure this, and keep it in for longer as necessary. Note: It is
recommended that a few batches of oil are prepared, so that the researcher may use one
that is room temperature, while another is cooling back down

20. Thoroughly clean the flask of oil residue.

21. Upload the data for thermocouples and power into excel. The watt meter unfortunately
does not have the capacity to store more than one data file.

5.2.5 Test Procedure With Material

1. Repeat steps 1 5 above.

2. If using concrete or paste, read step 3 below, else skip to step 4.

3. Prepare the concrete or paste samples by grinding the cylinder specimens in /2" WaferS,
and gently hammering the wafer in order to cleave the sample into sizes similar to peanut
brittle. Place the pieces into a tupperware container with the lid closed until needed for
test.

4. Add material to the flask in accordance with Table 5-1. If using paste or concrete, pat the
sample dry with an absorbent cloth before adding. This is to rid the sample of any free
moisture at its surface. Record the mass of the sample.

5. Add the batch of oil that was calibrated previously into the flask. The height of oil will be
slightly higher than in the calibration run, due to it being displaced by the addition of the
material. Note: The mass may be slightly less than the calibration run after pouring the oil
into the flask. Add a small amount of fresh oil if necessary.

6. Place the flask into position underneath the air motor apparatus, without the mount. Pull
the deeper thermocouple out of the mount 3 4 in from its original position, so that it will
not lodge onto the material. Put the wooden cover on the flask with the paddle, heater, and
thermocouples (one of them raised). Swiftly stab the raised thermocouple into the material
so that it resumes the same position it had during calibration, but fully embedded into the
sample. Fit the stir paddle into the chuck fitting on the air motor, and ensure that it
vertically passes through the center of the stir paddle hole on the mount. All of the
mounted accessories need to be in an identical position as the calibration run.

7. Start the stir paddle. Adjust the regulator so that there is a 6 psi driving pressure.

8. Ensure that there is close to zero thermal gradient within the flask. This is done by
observing the deep and middle thermocouple temperatures as the stir paddle turns. It may
take a few minutes of monitoring this, now that there is one thermocouple in the material
and one outside of it. Also, check that the temperature in the room is approximately equal
to the temperatures within the flask.









9. Turn off the data acquisition system after a final check of the internal flask gradients, and
any differential between the room and flask.

10. Begin experimentation by simultaneously initiating the readings for the thermocouples,
starting the heater (obtaining power measurements) and starting a timer. It needs to be
made certain that both systems are synchronized, so that the power measurement
coincides with the temperature measurement. This may take some trial running by the
researcher to check the time when the Daq Lab initiates its inputs. It does not occur the
moment that the "start logging" option is initiated.

11. Leave heater running for four minutes.

12. Unplug the heater from the watt meter at exactly four minutes, leaving the Daq Lab to
continue making measurements. After this, unplug the watt meter from the power outlet.
For the Watts Up PRO, the data will be saved to system, even though the meter was
abruptly unplugged from the wall. Note: The Watts Up PRO will begin to generate two
second intervals between readings if the meter is left plugged in for more than 17 minutes.
Therefore, the meter should be unplugged immediately after heating so that one second
intervals will be obtained to coincide with temperature readings.

13. Continue to obtain temperature readings for thermocouples for a duration of time in
accordance with Table 5-1.

14. After this time period has elapsed, press the escape button on the acquisition system to
end the logging.

15. Stop the stirrer, remove it from the chuck and remove the wooden mount (with all
components) from the flask. Set it, along with its mounted components onto a paper towel.
Wipe off any oil on the heater, stir paddle, and thermocouples.

16. Pour the oil from the flask, through a filter, and back into the 6"xl2" cylinder mould to
remove any material that is in suspension and place the cover on it.

17. Place the fluid into a refrigerator for about an hour to bring the temperature back down to
the room's value. Check to ensure this, and keep it in for longer as necessary.

18. Thoroughly clean the flask of oil residue.

5.2.6 Analysis

Note: This analysis section may be used to format either the calibration or material data file

1. After uploading the data file from the calibration and material run, trim out all of the
excessive columns that are included with the watt meter' s data. This includes everything
except for time, power (watts), and watt-hours.









2. Ensure that the entries were taken in one second intervals for both acquisition systems.
The uploaded data from the watt meter is usually given in units of hours. The Daq Lab
outputs 60 entries per written minute (one second per entry).

3. Trim out the initial (zero) power readings so that the first power entry, when the heater
was plugged in, matches with the first temperature reading. This synchronizes the data.

4. After synchronizing, convert all of the time entries into units of seconds.

5. Trim out the excessive readings of the synchronized data so that there are a total number
of data points (seconds) equal to that indicated by Table 5-1. For example, a lime rock
data file would have a total of anywhere from 625 sec 700 sec of data points.

6. Write an equation in a column that calculates the total energy outputted from the heater.
The equation that converts power to energy for each interval (one second) is indicated by
the following:


E, = I't -(,-t, ) + E, (5-4)


Where i indicates the time step, P indicates the power (Watts), t is the time (seconds), and
E is the energy (j oules). Copy this equation down the column until the last thermocouple
reading. One can convert to kiloj oules by multiplying the first term by the reciprocal of
1000.

7. Calculate the heat capacity (C) of the calorimeter (calibration run), and the calorimeter
with material (material run) as indicated in Equation 5-2. The values for AE and AT
(change in energy and temperature, respectively) are given by one of the three methods
outlined below Equation 5-2. Use the calculated energy.


C =(5-5)


Single value method. This method utilizes only one final and one initial measured value.
The AE term is calculated by subtracting the first energy term (should be zero) from the
final energy term. For AT, the initial reading of the deep and shallow thermocouple is
averaged, and subtracted from the final averaged temperature between the deep and
shallow thermocouple.

Average analysis (11 values). This method uses the last and first eleven measured
increments (seconds). The AE term is calculated by subtracting the average of the first
eleven energy terms from the average of the final eleven energy terms (in this case, the
final eleven energy terms should be the same). For AT, the first eleven readings of the
deep and shallow thermocouples are averaged (total of 22), and subtracted from the final
eleven averaged temperatures between the deep and shallow thermocouple (also a total of
22 values).










Average analysis (6 values). This method uses the last and first six measured increments
(seconds). The AE and AT terms are calculated the same as in the eleven value analysis,
except that the last and first six terms are used instead.

Moving average analysis (11 values). This method calculates the AE and AT terms by
taking the average of the surrounding 10 values about a point in time (five less and five
greater than the point. With the use of this approach, one can graphically depict the way
that the calculated specific heat changes as a function of time. Figure 5-4 and 5-5 show
examples of two temperatures that were calculated. The temperatures indicated here
represent both thermocouples' (one in the first column within the box and the other in the
second) readings at a well established equilibrium time. It should also be noted that both
the calibration run, and the material run need to be used in parallel with this method. In
other words, the moving average AT terms need to be calculated for both runs, in order to
compute the specific heat. The moving average for AE should be constant, due to the
heater being off at these times.

8. Calculate the specific heat (c) of the material by referring to Equation 5-3. The theoretical
specific heat should be calculated for each of the three analysis methods indicated above.



mn' (5-6)

Where mm is the mass of the material, CTot is the heat capacity obtained from the run that
included the material and calorimeter, and CCal is the heat capacity obtained from the run
that included the calorimeter by itself.

5.3 Transient Test

5.3.1 Calorimeter Accessories

* Interior bath Stainless steel beaker, 4000ml
* Interior bath oil Duratherm 600, heat transfer fluid
* Heater Gaumer, 500 Watt with screw plug
* Air Motor With a drill chuck attachment
* Stir paddle Powered by air motor
* Wooden Mount Used to cover the top of the interior bath and to mount accessories
* Exterior Bath Circulatory, to maintain constant temperature of 280C
* Exterior Bath Fluid Dowfrost heat transfer fluid
* Concrete Specimen 125 grams of concrete material


5.3.2 Data Instrumentation

* Data Acquisition Daq PRO, 5300
* Watt Meter Watts Up Pro, Power Analyzer
* Thermistor Purpose is to check the exterior bath' s ability to maintain 280C










* Thermocouples Three type J
* Scale Accurate to 0.1 grams


5.3.3 Cast Procedure

1. Cast 4 in by 8 in cylindrical specimens with caps to seal moisture

2. De-mold the cylinders at 24hrs +/- 1hr

3. Place the cylinders into a lime bath solution to provide a neutral curing environment for the
concrete. Withdraw them at necessary ages for testing

5.3.4 Test Procedure Calibration

1. Ensure that the beaker will sit in the exterior bath so that the top lip of it is above the level
of dowfrost fluid by about two inches. Place a step on the bottom of the bath if needed, in
order to hold the beaker at this level.

2. Engage the exterior circulating bath so that it is maintaining a constant temperature of
approximately equal to the room temperature. Note: Leave this temperature setting the
same for the material run.

3. Ensure that the Daq Lab is configured properly. This includes the following menus:
"System Configuration" ensure that input filter is on, that no average is taken, and that
temperature is in C.

"Setup the Logger" Ensure that the three inputs used are set to read as a type J
thermocouples. Also be sure that the rate is set to every second for 5,000 samples.

4. Warm up the data acquisition system for the thermocouples by turning it on and having it
read temperatures.

5. Ensure that the accessories are put into position on the wooden mount. Orient the
thermocouples so that one hovers over the bottom surface of the beaker, and the other is in
the center. Keep all of the accessories in the same positions for each run. Also, place one of
the three thermocouples outside of the beaker to read the air temperature.

6. Zero the beaker (without the mount), and leave it on the scale.

7. Check to ensure that the heat transfer oil is equal to the exterior bath temperature. Since the
exterior bath is set to the room temperature, it may be best to leave the oil in the room for
24 hours to allow equilibrium.

8. Add oil to the beaker, so that a two inch lip is left between the level of the oil and the top
edge. Record the mass of the oil.










9. Place the beaker into position within the exterior bath and underneath the air motor
apparatus.

10. Put the wooden cover on the beaker with the paddle, heater, and thermocouples placed into
position. Fit the stir paddle into the chuck fitting on the air motor, and ensure that it
vertically passes through the center of the stir paddle hole on the mount.

11. Start the stir paddle. Adjust the regulator so that there is a 6 psi driving pressure.

12. Ensure that there is close to zero thermal gradient within the beaker. This is done by
observing the deep and middle thermocouple temperatures as the stir paddle turns. Also,
check that the temperature in the exterior bath is equal to the temperatures within the
beaker. This may take a few minutes, but not an excessive amount of time, due to the oil
being at room temperature and the bath also being set to regulate itself at room
temperature.

13. Turn off the data acquisition system after a final check of the internal beaker gradients, and
any differential between the room and beaker.

14. Begin experimentation by simultaneously initiating the readings for the thermocouples,
starting the heater (obtaining power measurements) and starting a timer. It needs to be
made certain that both systems are synchronized, so that the power measurement coincides
with the temperature measurement. This may take some trial running by the researcher to
check the time when the Daq Lab initiates its inputs. It does not occur the moment that the
"start logging" option is initiated.

15. Leave heater running for three minutes.

16. Unplug the heater from the watt meter at exactly three minutes. After this, unplug the watt
meter from the power outlet. For the Watts Up PRO, the data will be saved to system, even
though the meter was abruptly unplugged from the wall. Note: The Watts Up PRO will
begin to generate two-second intervals between readings if the meter is left plugged in for
more than 17 minutes. Therefore, the meter should be unplugged immediately after heating
so that one second intervals will be obtained to coincide with temperature readings.

17. Seize the data acquisition of the temperatures. The calibration run for the transient test only
needs to last for three minutes.

18. Stop the stirrer, remove it from the chuck and remove the wooden mount (with all
components) from the beaker. Set it, along with its mounted components onto a paper
towel. Wipe off any oil on the heater, stir paddle, and thermocouples.

19. Pour the oil from the beaker into a 6"xl2" cylinder mould, place a cover on it, and label the
calibrated fluid.

20. Place the fluid into a refrigerator for about an hour to bring the temperature back down to
the room's value. Check to ensure this, and keep it in for longer as necessary. Note: It is










recommended that a few batches of oil are prepared, so that the researcher may use one that
is room temperature, while another is cooling back down

21. Thoroughly clean the beaker of oil residue.

22. Upload the data for thermocouples and power into excel. The watt meter unfortunately
does not have the capacity to store more than one data file.

5.3.5 Analysis Calibration

1. After all data from the calibration run has been uploaded to excel, trim out all of the
excessive columns that is included with the watt meter' s data. This includes everything
except for time, power (watts), and watt-hours.

2. Ensure that the entries were taken in one second intervals for both acquisition systems. The
uploaded data from the watt meter is usually given in units of hours. The Daq Lab outputs
60 entries per written minute (one second per entry).

3. Trim out the initial (zero) power readings so that the first power entry, when the heater was
plugged in, matches with the first temperature reading. This synchronizes the data.

4. After synchronizing, convert all of the time entries into units of seconds.

5. Trim out the excessive readings of the synchronized data so that there are a total number of
data points (seconds) equal to the total heating time plus two seconds. For example, a
concrete data file would have a total of 182 seconds for the calibration run.

6. Write an equation in a column that calculates the total energy outputted from the heater.
The equation that converts power to energy for each interval (one second) is indicated by
the following:


E = t-t-)+E-(51


Where i indicates the time step, P indicates the power (Watts), t is the time (seconds), and
E is the energy (j oules). Copy this equation down the column until the last thermocouple
reading. One can convert to kiloj oules by multiplying the first term by the reciprocal of
1000.

7. Calculate the heat capacity (C) of the calorimeter (calibration run), as indicated in Equation
5-2. Use the calculated energy.


C =(5-2)


AE is obtained by taking the energy at 182 seconds (should be the same as that at 181
seconds, but slightly more than 180, the shut off time) and subtracting the energy at zero
seconds from it (should be zero). For AT, the last three temperature readings for









thermocouples one and two are averaged (total of six values, from 180-182 seconds) and
the initial thermocouple readings (at time zero) are averaged and subtracted from the final.

5.3.6 Test Procedure With Material

1. Repeat steps 1 6 in Test Procedure Calibration.

2. Prepare the concrete samples by grinding the cylinder specimens in /2" WaferS, and gently
hammering the wafer in order to cleave the sample into sizes similar to peanut brittle. Place
the pieces into a tupperware container with the lid closed until needed for test.

3. Add material to the beaker in accordance with Table 5-1. Make sure to pat the concrete
sample dry with an absorbent cloth before adding. This is to rid the sample of any free
moisture at its surface. Record the mass of the sample.

4. Add the batch of oil that was calibrated previously into the beaker. The height of oil will be
slightly higher than in the calibration run, due to it being displaced by the addition of the
material. Note: The mass may be slightly less than the calibration run after pouring the oil
into the beaker. Add a small amount of fresh oil if necessary.

5. Place the beaker into position underneath the air motor apparatus, without the mount. Put
the wooden cover on the beaker with the paddle, heater, and thermocouples. Fit the stir
paddle into the chuck fitting on the air motor, and ensure that it vertically passes through
the center of the stir paddle hole on the mount. All of the mounted accessories need to be in
an identical position as the calibration run.

6. Start the stir paddle. Adjust the regulator so that there is a 6 psi driving pressure.

7. Ensure that there is close to zero thermal gradient within the beaker. This is done by
observing the deep and middle thermocouple temperatures as the stir paddle tumns. Also,
check that the temperature in the exterior bath is equal to the temperatures within the
beaker. It may take a few minutes of monitoring this, especially now that there is material
in the beaker.

8. Turn off the data acquisition system after a final check of the internal beaker gradients, and
any differential between the room and beaker.

9. Begin experimentation by simultaneously initiating the readings for the thermocouples,
starting the heater (obtaining power measurements) and starting a timer. It needs to be
made certain that both systems are synchronized, so that the power measurement coincides
with the temperature measurement. This may take some trial running by the researcher to
check the time when the Daq Lab initiates its inputs. It does not occur the moment that the
"start logging" option is initiated.

10. Leave heater running for three minutes (same as calibration run).

11. Unplug the heater from the watt meter at exactly three minutes, leaving the Daq Lab to
continue making measurements. After this, unplug the watt meter from the power outlet.










For the Watts Up PRO, the data will be saved to system, even though the meter was
abruptly unplugged from the wall. Note: The Watts Up PRO will begin to generate two
second intervals between readings if the meter is left plugged in for more than 17 minutes.
Therefore, the meter should be unplugged immediately after heating so that one second
intervals will be obtained to coincide with temperature readings.

12. Continue to obtain temperature readings for thermocouples for a duration of time in
accordance with Table 5-1.

13. After this time period has elapsed, press the escape button on the acquisition system to end
the logging.

14. Stop the stirrer, remove it from the chuck and remove the wooden mount (with all
components) from the beaker. Set it, along with its mounted components onto a paper
towel. Wipe off any oil on the heater, stir paddle, and thermocouples.

15. Pour the oil from the beaker, through a filter, and back into the 6"xl2" cylinder mould to
remove any material that is in suspension and place the cover on it.

16. Place the fluid into a refrigerator for about an hour to bring the temperature back down to
the room's value. Check to ensure this, and keep it in for longer as necessary.

17. Thoroughly clean the beaker of oil residue.

5.3.7 Analysis With Material

1. After all data from the material run has been uploaded to excel, trim out all of the excessive
columns that is included with the watt meter's data. This includes everything except for
time, power (watts), and watt-hours.

2. Ensure that the entries were taken in one second intervals for both acquisition systems. The
uploaded data from the watt meter is usually given in units of hours. The Daq Lab outputs
60 entries per written minute (one second per entry).

3. Trim out the initial (zero) power readings so that the first power entry, when the heater was
plugged in, matches with the first temperature reading. This synchronizes the data.

4. After synchronizing, convert all of the time entries into units of seconds.

5. Trim out the excessive readings of the synchronized data so that there are a total number of
data points (seconds) equal to the equilibrium time indicated in Table 5-1. For example, a
concrete data file would have a total of anywhere from 575 to 625 seconds for the material
run.

6. Write an equation in a column that calculates the total energy outputted from the heater.
The equation that converts power to energy for each interval (one second) is indicated by
the following:










P +P


Where i indicates the time step, P indicates the power (Watts), t is the time (seconds), and
E is the energy (j oules). Copy this equation down the column until the last thermocouple
reading. One can convert to kiloj oules by multiplying the first term by the reciprocal of
1000.

7. Calculate the heat capacity (C) of the calorimeter (calibration run), as indicated in Equation
5-2. Use the calculated energy.


C =(5-2)


AE is obtained by taking the energy at the Einal reading and subtracting the energy at zero
seconds from it (should be zero). For AT, a graph depicting the temperature vs. the time
needs to be constructed. The Einal value is equal to the intersection of the trend line for the
heat up period (from zero to 181 seconds) and the extrapolated trend line for the linear
transient period (the last 200 seconds of data). Figure 5-7 shows a graphical depiction of
this technique. Excel makes this possible by including an equation with the trend line. By
solving for these two equations for two unknowns, one may obtain the time and
temperature that they intersect. The initial thermocouple readings (at time zero) are
averaged and subtracted from the final extrapolated value, in order to get AT.

8. Calculate the specific heat (c) of the material by referring to Equation 5-3. The theoretical
specific heat should be calculated for each of the three analysis methods indicated above.

c = 1- (Cro, Coml) (5-6)
m,,

Where mn, is the mass of the material, Co,t is the heat capacity obtained from the run that
included the material and calorimeter, and Cco is the heat capacity obtained from the run
that included the calorimeter by itself.


5.4 Results and Discussion

5.4.1 Calorimeter Development and Sensitivity

As the calorimeter apparatus and testing procedures were being developed, several issues

were discovered. The air stirrer that was used for the flask test was not an immediate solution to

effectively diffusing heat throughout the flask. The first attempt was to use an electronic motor

as the driving mechanism for the stirring device. The problem with this apparatus was that it










produced an excessive and inconsistent amount of heat (from the motor resistivity) that was

conducted down the stirrer shaft, and into the calorimeter. As a consequence, the temperature

curves for this method displayed inconsistency that would lead to erroneous calorimetric

measurements. With this discovery, a stirring device that was powered by an air motor would be

developed and used in this test. By setting a bearing into the wooden mount (the cover of the

flask) to guide the rotations of the shaft, this would also serve to minimize the heat produced by

the stir paddle. For the insulated flask procedure, the calibration runs (without material) display a

near constant temperature after the heating is terminated (very slight thermal dissipation from

insulative imperfections), showing that the air stirrer was an effective device to use for this

application. As a result, this device was chosen as the chief diffuser of fluid for this test.

Another developmental issue with the flask test was establishing equilibrium between the

calorimeter and the material that was being tested. In order to calculate the specific heat of these

materials, it was essential that this state was established, in order to assume a homogenous

temperature. It was discovered that depending on the material tested for, various equilibrium

times were required. The key to this development was to balance characteristics between

equilibrium time and the amount of mass that was used. Although a small amount of mass would

allow for a shorter equilibrium time, other considerations needed to be made. The problem with

using too small of an amount of mass that would be tested within 3800 grams of fluid was that it

made the test sensitive to temperature error. As can be seen in Equation 5-6, the term 1 me, acts

as a multiplier of the differences between the AE AT terms, within the parenthesis. With this

being said, the 1 mn, term may amplify any error encountered with the thermocouples when a

small amount of mass is used. On the other hand, a large amount of mass leads to time duration

issues (for equilibrium), where other experimental error may come into play. Although the flask









is fully insulated, and negligible heat loss or input is assumed for relatively short time periods,

longer experimental durations (i.e., 1200 seconds) may lead to slight alterations in the

calorimetric conditions that result in more sporadic results.

With respect to the insulated flask test, the data analysis procedure for the different

materials evolved with trial and error. As indicated in the insulated flask analysis section above,

there were four different approaches that were used to analyze the data. The single value method

had the most flaws, due to it taking the average of two thermocouple readings at one particular

point in time. This was found to not be accurate enough, due to the noise involved with

thermocouple readings. This noise had the potential to throw off the value obtained for specific

heat by a considerable amount. For example, Table 5-7 depicts how the standard deviation for

the single value method is greater than the other methods.

The average methods (6 and 11 values) were then used, in order to help soften the noise of

the thermocouples. The procedures for these are also included in the insulated flask analysis

section above. The values proved to have less variation, due to the readings being averaged in

order to cancel the plus or minus variability in the thermocouple readings. However, due to only

one interval of values being used for the average, the method could be improved upon by taking

multiple intervals of average values and subsequently averaging them.

The Einal approach to getting a representative value for specific heat, involved taking the

average of the final Eive moving average values (see analysis procedure section and Figures 5-4

through 5-6). This method was determined to be the most accurate way of obtaining specific

heat, due to it involving the averages of several increments throughout the time period where the

material was in equilibrium with its surroundings. Although this method was the most desired, it










also displayed variability due to thermocouple noise. A plot showing the average specific heat as

a function of time is displayed in Figure 5-8.

5.4.2 Transient Test Complications

One of the issues that was encountered in using the transient test procedure was that the

linear state of temperature decrease was very difficult to locate. In doing several analyses, a

slight change in the interval for which the linear transient state was depicted would change the

value for AT to an extent where the value for specific heat would vary excessively. When

looking at Figure 5-7, one may note that because there is adequate heat conduction between the

two bath systems, the curve would continue to decay asymptotically until the temperature of the

interior bath would return to that of the exterior bath (that at time zero) This creates an infinite

amount of perspectives as to where the linear decay window of this curve should be located. In

fact, if one was to use a window of time where the two baths were nearly equal, than a value of

zero would be found for AT.

Although De Schutter's experiment appeared scientifically sound from what was presented

in the literature, the lack of procedural information made it hard to replicate in the lab. Another

setback for replication was that the fluid heptane (used by De Schutter, in his analysis) was too

toxic to use in this experiment. In place of Heptane, a nonreactive heat transfer fluid was used.

The results reported in Table 5-2 display the variability that was encountered in the transient test

approach. As a result of this variability, no viable conclusions could be drawn from this data.

5.4.3 Mix Materials and Parameters

The specific heat tests were carried out in order to analyze Florida limestone, sand, cement

paste, and concrete. While the insulated test was used to analyze all four materials, the transient

test was only attempted for the concrete samples. The data collected for the inert materials (no










hydration) consists of five rock and five sand sample tests. The data collected for the reactive

materials included two samples tested for each age of 1 day, 3 days, and 7 days curing time.

It was ensured that both the paste and concrete had the same water to cement ratio (w/c =

0.38). For the paste mix, Florida Portland Cement, Type I/II was used. The weights used for the

paste mix were 5 lbs of cement and 1.9 lbs of water. After mixing the paste by hand with gloves,

specimens were prepared in 2 in x 4 in cylinder moulds. The specimens were vibrated, covered

with plastic wrap, and left overnight to cure. They were demolded the following day, and set into

a lime water bath at the same temperature. When used for testing, they were reduced into smaller

pieces and the surface of the material was patted dry (see procedures above).

Table 5-3 indicates the proportions of materials used for the concrete mixture. The plastic

properties that were obtained included a slump of 5 in and an air content of 7%. The use of

superplasticizer and water reducing admixtures were needed in order to make the concrete

workable at a water to cement ratio of 0.3 8. After mixing these materials in a small drum mixer,

the specimens were prepared in 4 in x 8 in cylinder moulds. They were then sealed against

moisture loss and left overnight to cure. After 24 hours, they were demolded and placed in the

same lime bath as the paste samples until needed for testing.

5.4.4 Concrete Specimens

The results of the concrete tests for the insulated flask procedure are indicated in Tables 5-

4 through 5-5. While all the materials that were tested in the insulated flask displayed some

variability with respect to specific heat, the values formed a noticeable trend from which

conclusions could be drawn.

The flask test for concrete yielded results that were relatively consistent, when compared to

the other materials. Figure 5-9 shows a material run, where the temperature gradient is reduced

with time, until equilibrium is finally reached at about 625 seconds. Note that the curve which is









below the other one represents the thermocouple buried by the material. For the 1 day, 3 day and

7 day tests, the specific heats obtained from the moving average method were 1.45, 1.50, and

1.74 kj/kg~k, respectively. Figure 5-10 portrays how there was a noticeable increase in the

specific heat of concrete, particularly between 3 and 7 days of age.

This increase is thought to be due to the excessive ingress of water into the concrete as a

result of the reaction kinetics. With more water located within the specimen than was initially

present, the specific heat would inevitably increase due to water' s high value of 4. 186 kj/kg~k, as

long as this water were not to react to form different components. Although the water that reacts

with cement paste is used to make calcium silicate hydrate and calcium hydroxide, it is believed

that the reaction kinetics acted to drive excessive moisture (more than stoichiometrically

balanced) into the specimen.

It has been found (Ulm and Coussy, 1996) that as the cement and water hydration reactions

proceed, the water diffuses through the material from the regions of the hydrated cement towards

regions of unhydrated cement, where products form on an instantaneous manner, relative to the

timescale of the diffusion process (Figure 5-1 1). He also mentions that with respect to reaction

kinetics, the diffusion of water is said to be the most dominating mechanism of the hydration

reaction. In consideration of this, it would therefore not be expected that a linear increase in the

specific heat of concrete would occur with respect to age, but rather an exponential curvature of

increase. This is due to the reaction rate of the concrete being non-linear as well, brought about

by the acceleration of the hydration taking place due to the addition of not only more reactive

resource (water), but more heat (from the reaction itself) that acts as an accelerator in an

exothermic reaction. Therefore, the diffusion of the water may be thought of as accelerating.









These reaction kinetics especially hold true in concretes (or pastes) where the water to

cement ratio is lower than the ideal stoichiometric ratio. It has been found that the ideal range for

a water to cement ratio should be between 0.42 and 0.45, in order to get a complete reaction

between these components (Mindess et. al., 2003). The diffusion potential was therefore

substantial in this concrete mix, considering that the w/c ratio was mixed at 0.38.

5.4.5 Paste Specimens

The time that the cement paste took to reach equilibrium was similar to that of concrete, as

Figure 5-12 displays. The cement paste specimens also displayed analogous behavior to that of

the concrete specimens with regards to specific heat. The specific heat increased a considerable

extent between 3 and 7 days (Figure 5-13). As the 1 day (1.50 kj/kg~k) and two day (1.52

kj/kg~k) averages were nearly equivalent, the 7 day average (2.2 kj/kg~k) showed marginal

increase. The greater increase in specific heat (when compared to concrete) is thought to be due

to the greater concentration of cement paste, therefore causing a greater amount of moisture

diffusion to take place from the hydrated, towards the unhydrated regions within. The greater

increase in specific heat during the latter interval (3 to 7 days) may have been brought about by

the accelerated reaction kinetics (as occurred in the concrete specimens).

Similar to concrete, it is believed that the affinity for water, from the unreacted cement

paste within, created a saturation of the reacted media spaces (in the exterior region) with

moisture. As this moisture is only an addition to the previously reacted media, it serves as free

water, and therefore raises the specific heat.

5.4.6 Rock Samples

Although the equilibrium process of lime rock appeared a bit "rocky," the values for the

specific heat of lime rock had the least amount of variation (Figure 5-14). Table 5-8 summarizes

all of the runs that were carried out for this material, and Figure 5-15 graphically displays the










low variability and approximate average. Because these samples were dried in the oven

(something that couldn't have been done for the paste and concrete samples), the microstructure

of the test samples was very consistent. Another advantageous property of thi s material was that

the needed equilibrium time was not very long, considering there was 250 grams of material that

was used.

It was also found that the "standard" value for lime rock, 0.85 kj/kg~k, was not very far

off from what was obtained experimentally. The moving average results show that the specific

heat of the rock was 0.91 kj/kg~k, with a standard of deviation of 0. 149 that was obtained from

five test runs. It was essential to keep the rock (and other materials) in a dry place, where they

would acquire room temperature.

5.4.7 Sand Samples

Sand was the most difficult material to test, due to a long duration of time being needed for

thermal equilibrium to be established. Initially, 250 grams of material was used, where it was

observed that the diffusivity of heat into the sand took much longer than it was expected. The

amount of sand had to be reduced, in order to run the test in a shorter time interval that would not

create the error that would be incurred from longer intervals. It took 1200 seconds for only 100

grams of sample to reach equilibrium (Figure 5-16). Even though the sand was kept completely

dry, and at room temperature, the combination of these two factors (low mass and long duration)

was the cause of inconsistent results, as can be seen in Table 5-9. The average specific heat for

sand was 1.33 kj/kg~k, with a standard deviation of 0.91.

5.5 Summary and Conclusions

The transient experimental set-up was tried but found to be unsuccessful. This was due to

the inability to find a linear transient window of time that would be used to extrapolate for AT. It









was unclear how De Schutter and Taerwe's (1995) experiment could be replicated, but credit is

given to this research for it being a catalyst to develop the insulated flask test.

Although there are some improvements that may be made for the insulated flask test, the

procedures were successful in producing viable results for concrete, cement paste, and lime rock

when using the 11 value moving average analysis. With the onset of further hydration, and an

affinity for moisture, both the concrete and cement paste displayed an increase in measured

specific heat with respect to curing time. This increase in specific heat with time for the cement

paste and concrete is believed to be due to the ingress of water into the sample.

De Schutter and Taerwe (1995) found that paste samples sealed against moisture displayed

a decrease in specific heat with age due to moisture consumption. However, the samples used in

our study were stored in a lime bath where water was able to diffuse into the samples. Ulm and

Coussy (1996) indicate that water diffuses from regions of hydrated, towards regions of

unhydrated cement paste. It is believed that the measured specific heat of cement paste increased

more than that of concrete, because of the higher concentration of cement within the cement

paste samples. This occurred even though hydrated cement paste has a much less permeable

microstructure than that of concrete (Halamickova et al., 1995). The reason for placing the

samples into a 100% humidity environment in this research was to replicate the typical

requirements for many mass concrete pours, where the surfaces need to be kept wet and free

from moisture loss.

The results obtained for the specific heat of lime rock compared well with that of other

sources, at 0.91 kj/kg~k. This material fared well for the insulated flask test, due to the feasibility

in producing consistently dry, thermally stable, and thermally diffusible samples. Its higher

thermal diffusivity allowed the lime rock to undergo short flask tests with a relatively large










amount of material (250 grams). These were the factors that contributed to more consistent and

accurate results.

High variability in test results was obtained when the specific heat test was performed on

the sand samples. Due to sand's low thermal diffusivity, the mass had to be reduced and the

duration time had to be increased. The longer duration of the test introduced higher variability

because of heat loss to the environment and energy from the stirring paddle. With the use of a

smaller sample, the heat capacity of the sample is much smaller than the heat capacity of the

system. As a result, little variability in the test system would translate into a much greater

variability in the test results for a small sample.


Table 5-1. Equilibrium times for the flask test and transient test.


Mass (g) Total Heating Time (sec)
Material Dewar Transient Test Dewar Transient Test


Well Established
Equilibrium Time,
Including Heating (sec)
Dewar Transient Test

625 -
700 NA

1200 NA

725 -
750 NA

625 -
800 575 -625


Lime Rock

Sand

Cement
Paste


250

100


240

240


125 NA


240 NA


Concrete 125 250


240










Table 5-2. Specific heat and statistical results for transient test

Specific Average Specific
Age Heat Heat Per Day STDEV
Run Specimen (Day) (kj /kg~k) (kj /kg~k) Per Day

1 DeschConc(1),fl 1 1.600
1.011 0.832
2 DeschConc(2),f2 1 0.423

3 DeschConc(3),fl 3 2.420
2.717 0.420
4 DeschConc(4),f2 3 3.014

5 DeschConc(5),fl 7 2.118
2.005 0.161
6 DeschConc(6),f2 7 1.891


Table 5-3. Material weights used for concrete mix.
Water
Fine Coarse Reducing
W/C Aggregate Aggregate Cement Water Admixture Superplasticizer
Ratio (lb) (lb) (lb) (lb) (ml) (ml)
0.38 37.74 59.56 23.81 9.54 20 40


Table 5-4. Specific heat values for the insulated flask test for concrete.
Specific Heat (kj/kg~k)


Average of
Last 5
Moving
Averages

1.286

1.611

1.167

1.826

1.706

1.778


11 Values
(Avg)

1.319

1.414

1.142

1.664

1.690

1.837


6 Values
(Avg)

1.660

1.287

0.961

1.986

1.782

1.950


Run

1

2

3

4

5

6


Specimen

Conc(1),fl

Conc(2),f2

Conc(3), fl

Conc(4),f2

Conc(5),fl

Conc(6),f2


Age (Day)

1

1

3

3

7

7


Single Value

1.438

1.177

0.555

1.684

2.291

2.144











Table 5-5. Averages and standard deviation results for the insulated flask test for concrete.
Specific Heat (kj/kg~k)

STDEV, STDEV,
Single STDEV, STDEV, Moving Single 11 Moving
Age Value 11 Value 6 Value Average Value Value 6 Value Average
(Day) Method Method Method Method Method Method Method Method

1 0.185 0.067 0.263 0.229 1.307 1.366 1.473 1.449

3 0.799 0.369 0.725 0.466 1.120 1.403 1.473 1.497

7 0.104 0.104 0.119 0.050 2.218 1.764 1.866 1.742


Table 5-6. Specific heat values for the insulated flask test for cement paste.
Specific Heat (kj/kg~k)
Average of Last
Age Single 11 Values 6 Values 5 Moving
Run Specimen (Day) Value (Avg) (Avg) Averages

1 Paste(1l),fl 1 0.875 1.072 1.317 1.127

2 Paste(2),f2 1 1.754 1.765 1.824 1.872

3 Paste(3), fl 3 2.479 2.082 2.332 2.022

4 Paste(4),f2 3 0.975 1.011 1.071 1.013

5 Paste(5),fl 7 3.399 2.061 2.163 2.048

6 Paste(6),f2 7 3.007 2.302 2.500 2.310









Table 5-7. Averages and standard deviation results for the insulated flask test for cement paste.
Specific Heat (kj/kg~k)

STDEV, STDEV, STDEV,
Single 11 STDEV, 6 Moving Single 11 Moving
Age Value Value Value Average Value Value 6 Value Average
(Day) Method Method Method Method Method Method Method Method

1 0.622 0.490 0.359 0.527 1.314 1.418 1.571 1.499

3 1.064 0.758 0.891 0.713 1.727 1.547 1.702 1.518

7 0.277 0.170 0.238 0.186 3.203 2.182 2.332 2.179


Table 5-8. Results for the insulated flask test for lime rock.
Single Value 11 Value 6 Value Moving Average
Method Method Method Method
Run Specimen (kj /kg~k) (kj /kg~k) (kj /kg~k) (kj /kg~k)

1 Rock(2),f2 0.630 0.737 0.858 0.728

2 Rock(3),f3 1.092 0.940 1.079 0.929

3 Rock(4),fl 1.691 0.978 1.021 0.951

4 Rock(5),f2 1.668 1.106 1.179 1.123

5 Rock(6),f3 2.249 0.848 1.076 0.821

AVG 1.466 0.922 1.043 0.910

STDEV 0.621 0.139 0.118 0.149











Moving
Average
Method
(kj /kg~k)

0.779

0.056

2.055

2.229

1.546

1.333

0.909


6 Value
Method
(kj /kg~k)

1.366

0.320

2.067

2.381

1.700

1.567

0.795


Table 5-9. Results for the insulated flask test for sand.

Single Value 11 Value
Method Method
Run Specimen (kj /kg~k) (kj /kg~k)

1 Sand(9),f3 0.410 0.878

2 Sand(10O),fl 0.266 -0.074

3 Sand(11),fl 1.686 1.959

4 Sand(1 2),fl 2.727 2.187

5 Sand(13),f2 0.383 1.591

AVG 1.095 1.308

STDEV 1.081 0.918


Chr~onoeter


Heat TranF~er Fluid
5tir- Poddle '7


Polypropylene Glycol, kept at
29 C bay a circ~ulating both



Figure 5-1. Set up of the transient state calorimeter.




























Figure 5-2. Extrapolation technique (De Schutter and Taerwe, 1995) to acquire the temperature
change of the concrete.

Chronometer
IMotor-
Vott I Data
Meter I II Aquisition


H~atr -,~II I- M Thermocouples
-. --5Heat Trans~Fe~r F[luid
Stir Poddlel



Figure 5-3. Set up of the insulated calorimeter.













600 698 O
601 599 O
602 600 0
603 601 0
604 602 O
605 603 O
606 604 O
607 605 O
BOB 606 O
609 607 O
610 608 O
611 609 O
612 610 0
613 611 0
614 612 O
615 613 O
616 614 O
617 615 O
618 616 O
619 617 O
620 618 O
621 619 O
622 620 0
623 621 0
624 622 O
625 623 O
626 624 O
627 625 0
628 626 O
629 627 O
630 628 O
631
632
14et d 4et


32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32.5 117.3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32.5 117.3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099
32 5 117 3099


598 44 482 44.806 30 027
599 44 725 44.671 29 828
600 44 563 44.779 30
601 44 536 44 BB 30 027 TilG GSC)
602 44 428 44.698 30 1E
603 44 779 44.698 30
604 144 B 446711 30 Te~rfucouple 80)
605 44 779 4*LB 30 18
606 44 779 44644 30 1
607 44 T 44.617 3 8 ne
608 725 44.563 10 054 InerinOCOUplB L (C)
0E 44 59 44.563 30 135
610 44 617 44.BOF/ 30 1
611 44.617 44.72 3 7
612 44 59 4M.52 J 027
613 44 59 4.617 /30 054
614 44 663 44.914/ 29 828
615 44566 44.6 4 30 081
616 44 _z 4- 1,1 30 162
617r 44 698 44.7527 30 162
618 44 671 44 59 29 828
619 44 833 44.536 29 828
620 44.644 44.482 30.027
621 44 833 44.698 30 216
622 44 833 44.563 30 135
623 44 806 44.752 30 162
624 44 833 44.563 29 801
625 44 644 44.644 30
626 44 428 44.698 30 189
627 44 536 44.644, 30 081
628 44 617 44.779 30 243


Figure 5-4. The temperatures within the box (oC) represent those that are averaged for the point
of 622 seconds (indicated immediately left of the box).















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597 II 32 117 Illi 597 44 644 244 64 2 7
698 11 32 117 His9 59 44 482 -1 li 0 2
599 II 32 117 309 59 44 725 44 67 I
600 II 32 117 Illi 1111 44 563 244 -1 3
601 11 32 117 Illi Ill 44 536 -1- 86 3 I
602 II 32 117 Illi IL2 44 428 44[ 69 1
603 II 32 117 Illi II3 44 779 44[ 69
604 11 32 117 Ilid 114 44 86 44 01 3
605 II 32 117 Illi 6l" 44 779 44 69 1 8
606 11 c2 117 Illi Ill 44 779 41 44 3 8
607 11 32 117 Ilid 11' 44 779 44 1 3 8
608 II 32 117 Illi II8 44 725 44 56 3005
11 609 11 c2 117 Illi Ill 44 59 4 5 3 5
610 11 32 117 Ilid 611 44 617 44 I0 1 13
611 II 32 117 Illi 611 44 617 4 7 3 2
612 11 32 117 Ili 612 44 69 44 75 c
613 11 32 117 Ili 613 44 69 4 617 I0 Ic
614 II 32 117 Illi 614 44 563 44 914 2 2
615 11 32 117 Il9 61 l 44 563 44 44 3 8
616 II 32 117 Ild 616 44 482 44 I7 li16
617 II 32 117 Illi 617 44 698 44 75 I0 li
618 11 32 117 Illi 611 44671 4451: 82
619 II 32 117 Ild 6191 44833 44-6 92
620 II 32 117 Illi II0 44644 4442 07
621 11 32 117 Illi 61 44 833 -491 321
622 II 32 117 H09 622 44833 4453 303
623 II 32 117 Illi 623 44806 4472 I li
624 11 32 117 H09 624 44833 4453 290
625 II 32 117 Ill i 2 44 644 044
626 1 c 511739 Ili 44428 4491 308
627 11 32 117 Illi 627 44536 445441 08
628 II 32 117 Illi 628 44617 44-'< 3 43



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Figure 5-5. The temperatures within the box (OC) represent those that are averaged for the point

of 623 seconds. This is the last possible point that may be averaged using eleven

values.


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SUM X J f =AVERAGE(C68B C692)
A B| AVERAGE(numberl, numberr2, ...)| E F H II J K L M NT
Moving Average (11 Values)

1Tirne (Point) Avy Temp Specific Heat
II3 44) 6 1 18 1 ci 433
ill4 44) _1245 1 457 1
ill= 44) l i II7 1 6 0 211
6ll 44) _14 1 --1) 14
II7 44) 1804 4 '1 11 1 1

1Ill 44 I I8722 I4 513
6ll 44 6 L 1 43462
611 44 65277 I 4 I 58
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II4 44 55) 1 4 1 Illici 4
61 44) l illll81 I c) [75
6 4411 1 127 1 c7388

Aveag of Last 45 Averages0
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Figure 5-6. The specific heat is obtained by averaging the final five values (boxed in) that were

obtained by using the moving average method. Note that each "Avg Temp" was

calculated using the examples in Figures 5-5 and 5-6.


111~


























- t' r- .'" -4


Figure 5-7. Typical extrapolation technique used for the transient test, in order to obtain AT2.



14



























710 715 720 725 730 735




Figure 5-8. Moving average for a 7 day cement paste sample, where each point represents the
specific heat obtained from the average of eleven temperatures.


-HeatUp
-Nonlinear Tra nsince
-- Lherar Transience
S- Lh ear (Linear Transince)
-Lhar(Heat Lt.)


100 200 300
Sie


400 500 600





-Templ(T)
-Temp2(T)~


0 100 200 300 400 500 800 700
See



Figure 5-9. Typical curves depicting the establishment of thermo-equilibrium within the flask
calorimeter, in using concrete specimens.


2.000

1.800



1.400

1.200







0.600



0.400

0.200


Figure 5-10. The evolution of concrete specific heat with age, in using the moving average
method.














..,,Free Water

.~ Hydrates

I~ i/ Unhydrated Cement







Figure 5-11i. Hydration sketch of microdiffusion of free water through layers of already formed
hydrates to unhydrated cement.












--Templ(T)
-Tem2(T


0 100 200 300 400
Sie


500 600 700 800


Figure 5-12. Typical curves depicting the establishment of equilibrium for the paste samples
within the flask calorimeter.





0 1 2 3 4 5 6 7 8
Days


Figure 5-13. The evolution of cement paste specific heat with age, in using the moving average
analysis method.


2.500


0 100 200 300 400 600 600 700
Sie



Figure 5-14. Curves depicting the establishment of thermo-equilibrium for lime rock within the
flask calorimeter.






























0.400



0.200 -



0.800









1 2 3 4 6
Ricn

Figure 5-15. The results obtained from 5 individual specific heat runs for lime rock.























40









313









CHAPTER 6
SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS

6.1 Summary and Conclusions

6.1.1 Flexural Test

* The results from the beam tests using surface mounted strain gages show that it is feasible
to run this test on early age concrete.

* Consistent stress-strain plots can be obtained from this test.

* The measured tensile strength and elastic modulus in tension and compression increased
and the tensile strain capacity decreased from one day to three day ages.

* The compressive elastic modulus, obtained from the beam test compared well to the
estimated elastic modulus from compressive strength using the ACI equation (see Equation
4-7), and the measured elastic modulus from compression cylinders.

* The compressive elastic modulus was higher than the tensile elastic modulus. This is
believed to be due to additional micro-cracking in the tension region that produced a flatter
curve for the stress versus strain relationship. The observed difference between the
measured strains in the tensile zone versus the compressive zone warrants further
investigation into this area.

6.1.2 Specific Heat Test

* The transient experimental set-up was tried but found to be unsuccessful. This was due to
the inability to find a linear transient window of time that would be used to extrapolate for
AT.

* The procedures that were developed for the insulated flask test were successful in
producing viable results for concrete, cement paste, and lime rock when using the 11 value
moving average analysis.

* With the onset of further hydration and an affinity for moisture, both the concrete and
cement paste displayed an increase in specific heat with respect to curing time. This is
believed to be due to the ingress of water into the sample, as was studied by Ulm and
Coussy (1996).

* It is believed that the measured specific heat of cement paste increased more than concrete
because of the higher concentration of cement within the cement paste samples.

* Lime rock fared well for the insulated flask test, due to the feasibility in producing
consistently dry and thermally diffusible samples. Its higher thermal diffusivity allowed
the limerock to undergo short flask tests with a relatively large amount of material (250
grams). These were the factors that contributed to more consistent and accurate results.










* High variability in test results was obtained when the specific heat test was performed on
the sand samples. Due to sand's low thermal diffusivity, the mass had to be reduced and
the duration of time had to be increased. The longer duration of the test introduced higher
variability because of heat loss to the environment and energy from the stirring paddle.
With the use of a smaller sample, the heat capacity of the sample is much smaller than the
heat capacity of the system. As a result, little variability in the test system would translate
into a much greater variability in the test results for a small sample.

6.2 Recommendations for Further Research

6.2.1 Characterization of Maturity

* For both of the tests that were developed, additional measurements could be made in order
to classify the relative age (also known as maturity) of the concrete. With the use of
thermocouples placed into the centroid of these specimens, the temperature may be
measured with respect to time. By acquiring the history of temperature vs. time for a
concrete specimen, the maturity may be calculated and is related to the area under this
curve.

6.2.2 Flexural Test

* It is recommended that the acquired stress and strain data should be automatically
synchronized, so that the stress and strain at a particular gage point may be more reliably
matched with one another. This may involve the use of a single computer (as opposed to
two) in order to relate these parameters.

* A study should be conducted, that involves the nonlinear stress versus strain behavior of
the tensile and compression regions for the flexural test in early age concrete. The issues to
address include the adjustment of the neutral axis and moment of inertia (cracked versus
uncracked) as the specimen is being loaded. The early age of these specimens makes them
more vulnerable to alterations of these parameters as a function of load magnitude.

6.2.3 Specific Heat Test

* Due to the sensitivity to error, more precise and less sporadic temperature measurements
may be needed with instrumentation such as thermistors or resistance temperature
detectors (RTDs).

* For the flask test, produce a minimum amount of heat transfer between the calorimeter and
surrounding environment. This may involve more insulation or a more consistent stirring
mechanism. By combining these improvements with a larger collection of test data, the
averages for specific heat should further converge upon a representative value.

* Use a different amount of values to calculate a moving average. For instance, a more
representative moving average specific heat might include data with less or more points
than was done in our study (i.e. 7, 9, 13, or 15, as opposed to 11).










* Measure the amount of water within the samples at each test day, so that the ingress of
moisture may be known and accounted for in the specific heat calculations. This can be
done by oven drying the specimens and observing the change in moisture with respect to
age. With these results, a componential specific heat analysis can be carried out. This
includes accounting for the masses of all the materials (including water) so that a
componential specific heat of concrete may be compared with a measured specific heat of
concrete specimens.

* Calibrate the test system using a material sample of known specific heat, such as copper.










LIST OF REFERENCES

ACI Committee 207 (2005), 207.1R-05: "Guide to mass concrete. Farmington Hill, USA.

Al-Kubaisy, M.A., and Young, A.G. (1975). "Failure of concrete under sustained tension." Ma'~g.
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Ballim, Y. A. (2003). "A numerical model and associated calorimeter for predicting temperature
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Bamsforth, P.B. (1984). "Mass concrete." Concrete Society Digest, no 2, Concrete and Cement
Association.

Bentz, D.P., and Jenson, O.M. (2004). "Mitigation strategies for autogenous shrinkage cracking."
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Brooks, J.J., and Neville, A.M. (1977). "A comparison of creep, elasticity and strength of
concrete in tension and compression." Mag. Concr. Res., 29(100), 131-141.

Burg, R.G., and Ost, B.W. (1994). "Engineering properties of commercially available high-
strength concrete (including three-year data)." Research and Development Bulletin RD104,
Portland Cement Association, Skokie, Illinois, U.S.A.

Burg, R.G., and Fiorato, A.E. (1999). "High-strength concrete in massive foundation elements."
Research and Development Bulletin RD 117, Portland Cement Association, Skokie,
Illinois, U.S.A.

Clayton, N. (1978). "Fluid-pressure testing of concrete cylinders." Mag. Concr. Res., 30(102),
26-30.

De Schutter, G. (1999). "Degree of hydration based Kelvin model for the basic creep of early age
concrete." Mater. Struct., 32(218), 260-265.

De Schutter, G. (2002). "Finite element simulation of thermal cracking in massive hardening
concrete elements using degree of hydration based material laws." Comput. Struct., 80,
2035-2042.

De Schutter, G., and Taerwe, L. (1995). "General hydration model for Portland cement and blast
furnace slag cement." Cem. Concr. Res., 25(3), 593-604.

De Schutter, G., and Taerwe, L. (1995). "Specific heat and thermal diffusivity of hardening
concrete." Mag. Concr. Res., 47(172), 203-8.

Elvery, R.H., and Haroun, W. (1968). "A direct tensile test for concrete under long or short term
loading." Mag. Concr. Res., 20(63), 111-116.

Faria, R. (2006). "Modelling of concrete at early ages: Application to an externally restrained
slab." Cem. Concr. Compos., 28, 572-585.










Grasley, Z.C. (2003). "Embedded sensors for measuring internal relative humidity in concrete."
A Report of an Investigation, Department of Civil Engineering, UIUC.

Halamickova, P., Bentz, D.P., and Garboczi, E.J. (1995). "Water permeability and chloride ion
diffusion in Portland cement mortars: relationship to sand content and critical pore
diameter." Cem. Concr. Res., 25, 790-802.

Houghton, D.L. (1976). "Determining tensile strain capacity of mass concrete." J. Am. Concr.
Inst., 73(12), 691-700.

Kim, Jang-Ho Jay, Jeon, Sang-Eun, and Kim, Jin-Keun (2002). "Development of new device for
measuring thermal stresses." Cem. Concr. Res., 32, 1645-1651.

Klein, A., et al. (1963). "Thermal properties of mass concrete during adiabatic curing."
Symposium on Ma~ss Concrete. American Concrete Institute, Detroit, Michigan, 199-218.

Laplante, P., and Boulay, C. (1994). "Evolution of the thermal expansion coefficient of concrete
as a function of its maturity at very early age." Mater. Struct., In French, 27(174), 596-605.

Lee, H., et al. (2005). "The formation and role of ettringite in lowa highway concrete
deterioration." Cem. Concr. Res., 35, 332-343.

Lee, K.M., et al. (2006). "Autogenous shrinkage of concrete containing granulated blast-furnace
slag." Cem. Concr. Res., 36, 1279-1285.

Malhorta, V.M., and Mehta, P.K. (1996). Pozzolan2ic and' cementitious materials. Gordon and
Breach Publishers, Amsterdam, 113.

Mead, A.R. (1963). "Temperature-Instrument Observations at Pine Flat and Folsom Dams."
Symposium on Ma~ss Concrete. American Concrete Institute, Detroit, Michigan. 151-178.

Mindess, S., Young, J.F., and Darwin, D. (2003). Concrete. 2nd ed., Pearson Education, Inc.,
Upper Saddle River, NJ., 261-264 and 296-300.

Mindess, S., et al. (2005). "The nitrogen gas tension test of concrete." Proceedings of
Construction Materials and Mindess Symposium, Vancouver, B.C., Aug. 22-24, 2005.

Naik, T.R., Singh, S.S., and Hossain, M.M. (1994). "Permeability of concrete containing large
amounts of fly ash." Cem. Concr. Res., 24(5), 913-922.

Nakamura, H., et al. (1999). "Estimation of thermal crack resistance for mass concrete structures
with uncertain material properties." ACI Struct. J., 96(4), 509-518.

Nasser, K.W., and Lohtia, R.P. (1971). "Mass concrete properties at high temperatures." J. Am.
Concr. Inst., 68(3), 180-186.

Nianxiang, X., and Wenyan, L. (1989). "Determining tensile properties of mass concrete by
direct tensile test." ACI2ater. 1., 86(3), 214-219.










Qian, X., and Li, Z. (2001). "The relationships between stress and strain for high-performance
concrete with metakaolin." Cem. Concr. Res., 31, 1607-1611.

Ramlochan, T., et al. (2003). "The effect of pozzolans and slag on the expansion of mortars
cured at elevated temperature, Part I: Expansive behavior." Cem. Concr. Res., 33, 807-814.

Ramlochan, T., et al. (2004). "The effect of pozzolans and slag on the expansion of mortars
cured at elevated temperature, Part II: Microstructural and microchemical investigations."
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Reinhardt, H.W., Cornelissen, H.A.W., and Hordijk, D.A. (1986). "Tensile tests and failure
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ties." Cem. Concr. Res., 34(9), 1675-1681.

Sant, G., Lura, P., and Weiss, J. (2005). "Measurement of volume change in cementitious
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tensile strain capacity of concrete at early age." Cem. Concr. Res., 33(12), 2077-2084.

Townsend, C.L. (1981). Control of Cracking in 2a~ss Concrete Structures. U.S. Department of
the Interior Bureau of Reclamation, Washington, D.C.

Ulm, F., and Coussy, O. (1995). "Modeling of thermomechanical couplings of concrete at early
ages." J. Eng. M~ech., 121(7), 785-794.

Ulm, F., and Coussy, O. (2001). "What is a massive concrete structure at early ages? Some
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221-228.

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Report of an Investigation, Report no. 68-17, Structural Engineering Laboratory,
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BIOGRAPHICAL SKETCH

Samuel J. Smith received a degree in civil engineering at the University of Florida in the

summer of 2005. During the previous summers of acquiring this degree, he pursued internships

in the field as a surveyor, where he gained field knowledge with respect to road and bridge work.

Following this, Sam interned at Gerding Engineering Corporation, where he was involved in

structural design. He continued his education at the University of Florida the following fall and

procured his Master of Engineering in Civil Engineering in the summer of 2007. He aspires to

become a consultant in the field of structural engineering.





PAGE 1

1 THE DEVELOPMENT OF THERMAL AND MECHANICAL PROPERTY TESTS FOR MASS CONCRETE By SAMUEL J. SMITH A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING UNIVERSITY OF FLORIDA 2007

PAGE 2

2 2007 Samuel J. Smith

PAGE 3

3 ACKNOWLEDGMENTS Thank you Dr. Birgisson, Dr. Tia, Dr. Lybas, George Lopp, Chuck Broward, Chris Ferrarro, Charles Ishee, Colin Swaysland, Nabil Hossin ey, and all of my peers. Your help and support is greatly appreciated.

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4 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ ............... 3 LIST OF TABLES ................................ ................................ ................................ ........................... 7 LIST OF FIGURES ................................ ................................ ................................ ......................... 8 ABSTRACT ................................ ................................ ................................ ................................ ... 11 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .................. 13 1.1 Problem Description ................................ ................................ ................................ ...... 13 1.2 Fully Insulated Case ................................ ................................ ................................ ...... 14 1.3 Non Insulated Case ................................ ................................ ................................ ....... 16 1.4 Tests Developed ................................ ................................ ................................ ............ 17 1.4.1 Specific Heat ................................ ................................ ................................ ..... 17 1.4.2 Flexural Test ................................ ................................ ................................ ...... 19 1.5 Main Objectives of Study ................................ ................................ .............................. 20 1.6 Scope of Work ................................ ................................ ................................ ............... 20 2 SURVEY OF SPECIFICATI ONS ................................ ................................ ......................... 28 2.1 Introduction ................................ ................................ ................................ ................... 28 2.2 State Specifications ................................ ................................ ................................ ....... 28 2.3 Gover nment Agencies ................................ ................................ ................................ ... 31 2.3.1 U.S. Army Corps of Engineers ................................ ................................ ......... 31 2.3.2 U.S. Bureau of Reclamation ................................ ................................ ............. 32 3 LITERATURE REVIEW ................................ ................................ ................................ ....... 35 3.1 Overview of Issues with Mass Concrete ................................ ................................ ....... 35 3.2 Heats of Hydration ................................ ................................ ................................ ........ 36 3.2.1 Temperature Prediction in Mass Concrete ................................ ........................ 37 3.2.2 Low Heat Cements ................................ ................................ ............................ 40 3.2.3 Mineral Admixtures ................................ ................................ .......................... 41 3.2.4 Other Methods to Lessen Heat ................................ ................................ .......... 42 3.3 Cracking ................................ ................................ ................................ ........................ 43 3.4 Mechanical Effects of Temperature and Relative Humidity Gradients ........................ 44 3.4.1 Internal Restraints ................................ ................................ ............................. 45 3.4 .2 External Restraints ................................ ................................ ............................ 46 3.4.3 Temperature Related Restraint ................................ ................................ ......... 46 3.4.4 Relative Humidity Related Restraint ................................ ................................ 49 3.4.4.1 Autogenous shrinkage ................................ ................................ ........ 50

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5 3.4.4.2 Drying shrinkage ................................ ................................ ................ 50 3.4.4.3 Combinational effects ................................ ................................ ......... 51 3.5 Chemical Effects of Extreme Temperature and Relative Humidity ............................. 51 3.5.1 Immediate Effects ................................ ................................ ............................. 52 3.5.2 Long Term Effects ................................ ................................ ............................ 55 3.6 Measuring Mechanical Properties of Mass Concrete ................................ .................... 56 3. 6.1 Tensile Strength ................................ ................................ ................................ 58 3.6.1.1 Direct tensile tests ................................ ................................ ............... 58 3.6.1.2 Indirect tensile tests ................................ ................................ ............ 61 3.6.1.3 Hydro static force induced tension tests ................................ ............. 63 3.6.1.4 Flexural test ................................ ................................ ........................ 64 3.6.2 Tensile Strain and Elasticity ................................ ................................ .............. 64 3.6.3 Creep ................................ ................................ ................................ ............ 65 3.7 Measuring Thermal Properties ................................ ................................ ...................... 66 3.7.1 Coefficient of Thermal Expansion ................................ ................................ .... 66 3.7.2 Specific Heat ................................ ................................ ................................ ..... 67 3.7.3 Thermal Diffusivity ................................ ................................ ........................... 68 3.7.4 Heat Production and Heat Production Rate ................................ ...................... 68 3.8 Summary ................................ ................................ ................................ ....................... 69 4 FLEXURAL TEST FOR EARLY AGE C ONCRETE ................................ .......................... 83 4.1 Background ................................ ................................ ................................ ................... 83 4.1.1 Early Age Concrete ................................ ................................ ........................... 83 4.1.2 T hird Point Loading Scheme ................................ ................................ ............ 83 4.1.3 Compression Test for Elastic Modulus ................................ ............................. 84 4.2 Flexural Test Materials ................................ ................................ ................................ 84 4.2.1 Instrumentation ................................ ................................ ................................ 84 4.2.2 Sample Accessories ................................ ................................ ........................... 85 4.2.3 Preparation Accessories ................................ ................................ .................... 85 4.3 Flexural Test Procedure ................................ ................................ ................................ 85 4.3.1 Casting ................................ ................................ ................................ ............ 85 4.3.2 Sample Pr eparation and Storage ................................ ................................ ....... 86 4.3.3 Testing ................................ ................................ ................................ ............ 86 4.3.4 Data Analysis ................................ ................................ ................................ .... 86 4.4 Results and Discussion ................................ ................................ ................................ .. 88 4.5 Summary and Conclusions ................................ ................................ ............................ 90 5 SPECIFIC HEAT FOR EARLY AGE CONCRETE AND ITS COMPONENTS ................ 97 5.1 Background ................................ ................................ ................................ ................... 97 5.2 Insulated Flask Test ................................ ................................ ................................ ....... 99 5.2.1 Calorimeter Acce ssories ................................ ................................ .................... 99 5.2.2 Data Instrumentation ................................ ................................ ....................... 100 5.2.3 Cast Procedure ................................ ................................ ................................ 100 5.2.4 Test Procedure Calibration ................................ ................................ ........... 100 5.2.5 Test Procedure With Material ................................ ................................ ...... 102

PAGE 6

6 5.2.6 Analysis 103 5.3 Transient Test ................................ ................................ ................................ .............. 105 5.3.1 Calorimeter Accessories ................................ ................................ .................. 105 5.3.2 Data Instrumentation ................................ ................................ ....................... 105 5.3.3 Cast Procedure ................................ ................................ ................................ 106 5.3.4 Test Procedure Calibration ................................ ................................ ........... 106 5. 3.5 Analysis Calibration ................................ ................................ ..................... 108 5.3.6 Test Procedure With Material ................................ ................................ ...... 109 5.3.7 Analysis With Material ................................ ................................ ................ 110 5.4 Results and Discussion ................................ ................................ ................................ 111 5.4.1 Calorimeter Development and Sensitivity ................................ ...................... 111 5.4. 2 Transient Test Complications ................................ ................................ ......... 114 5.4.3 Mix Materials and Parameters ................................ ................................ ........ 114 5.4.4 Concrete Specimens ................................ ................................ ........................ 115 5.4.5 Paste Specimens ................................ ................................ .............................. 117 5.4.6 Rock Samples ................................ ................................ ................................ .. 117 5.4.7 Sand Samples ................................ ................................ ................................ .. 118 5.5 Summary and Conclusions ................................ ................................ .......................... 118 6 SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS ................................ ....... 134 6 .1 Summary and Conclusions ................................ ................................ .......................... 134 6.1.1 Flexural Test ................................ ................................ ................................ .... 134 6.1.2 Specific Heat Test ................................ ................................ ........................... 134 6.2 Recommendations for Further Research ................................ ................................ ..... 135 6.2.1 Characterization of Maturity ................................ ................................ ........... 135 6.2.2 Flexural Test ................................ ................................ ................................ .... 135 6.2.3 Specific Heat Test ................................ ................................ ........................... 135 LIST OF REFERENCES ................................ ................................ ................................ ............. 137 BIOGRAPHICAL SKETCH ................................ ................................ ................................ ....... 141

PAGE 7

7 LIST OF TABLES Table page 2 1 Limiting conditions, indicated in mass concrete specifications taken from various ................................ ................................ ................................ ............................... 33 2 2 Required amounts of mineral admixtures, indicated in mass concrete specifications ................................ ................................ ................................ 34 3 1 Contribution of cement compounds to overall cement hydrati on ................................ ..... 71 3 2 Properties of typical co urse aggregates ................................ ................................ ............. 72 3 3 Estimation of tensile strain capa city ................................ ................................ ................. 72 4 1 Material weights used. ................................ ................................ ................................ ....... 91 4 2 Mix proportions used, according to PCA recommendations. ................................ ............ 91 4 3 Mechanical properties for three day aged cylinders. ................................ ......................... 91 4 4 Mechanical properties for the beam. ................................ ................................ .................. 91 4 5 Standard deviation for various tests and ages. ................................ ................................ ... 92 5 1 Equilibrium times for the flask test and transient test. ................................ ..................... 120 5 2 Specific heat and statistical results for transient test ................................ ....................... 121 5 3 Material weights used for concrete mix. ................................ ................................ .......... 121 5 4 Specific heat values for the insulated flask test for concrete. ................................ .......... 121 5 5 Averages and standard deviation results for the insulated flask test for concrete. .......... 122 5 6 Specific heat values for the insulated flask test for cement paste. ................................ ... 122 5 7 Averages and standard deviation results for the insulated flask test for cement paste. ... 123 5 8 Results for the insulated flask test for lime rock. ................................ ............................. 123 5 9 Results for the insulated flask test for sand. ................................ ................................ .... 124

PAGE 8

8 LIST OF FIGURES Figure page 1 1 Graphical depiction of stress exceeding the strength within a certain region of mass concrete. ................................ ................................ ................................ ............................. 21 1 2 Temperature effects on fully insulated mass concrete. ................................ ...................... 22 1 3 Relative humidity effects on fully insulated mass concrete. ................................ .............. 22 1 4 Depiction of heat flow in an insulated case. ................................ ................................ ...... 23 1 5 Depiction of moisture state in an insulated case. ................................ ............................... 23 1 6 Temperature effects on non insulated mass concrete in one dimension. ........................... 24 1 7 Relative humidity effects on non insulated mass concrete in one dimension. ................... 24 1 8 Depiction of heat flow in a non insulated case. ................................ ................................ 25 1 9 Depiction of moisture flow in a non insulated case. ................................ .......................... 25 1 10 Set up of the transient state calorimeter. ................................ ................................ ............ 26 1 11 Set up of the insulated calorimeter. ................................ ................................ .................... 26 1 12 Loading scheme for the third point beam test, and accompanying moment diagram. ...... 27 3 1 Vertical temperature gradients vs. time, within a dam lift ................................ ................ 73 3 2 Vertical temperature gradients vs. time, b etween several lifts ................................ ......... 73 3 3 Effect of minimum dimension and replacement % of fly ash on t emperature rise ........... 74 3 4 Effect of minimum dimension and replacement % of BFS on temperature rise ............. 74 3 5 Thermal constraint device. ................................ ................................ ................................ 7 5 3 6 Effect of internal relative humidity on capillary tension. ................................ .................. 75 3 7 Compressive strength vs. time of heat exposure. ................................ ............................... 76 3 8 Elastic strain vs. time of heat exposure. ................................ ................................ ............. 76 3 9 Graphs depicting compressive strength for concrete subject to high temperature. ........... 77 3 10 Graphs depicting the elastic modulus for concrete subject to high temperature. .............. 77

PAGE 9

9 3 11 C oncrete tension specimen ................................ ................................ ............................... 78 3 12 Concrete specimen with notches. ................................ ................................ ....................... 78 3 13 L arge and small specimens. ................................ ................................ ............................... 79 3 14 A simple two piece mould, with claw like embedments. ................................ .................. 79 3 15 The IDT test, with a sample of asphalt concrete. ................................ ............................... 80 3 16 Sectional view of t he nitrogen gas test, with a diagram of principle stresses. ................... 80 3 17 Typical stress strain curves for concrete in tension. ................................ .......................... 80 3 1 8 Kelvin chain model ................................ ................................ ................................ ............ 81 3 19 Schematic drawing of a calorimeter used to measure specific heat ................................ ... 81 3 20 Schematic drawing of a cal orimeter used to measure thermal diffusivity. ........................ 82 3 21 Schematic drawing of a calorimeter used to measure the heat of cement hydration. ........ 82 4 1 Theoretical stress and strain distribution through cross section ................................ ........ 92 4 2 Loading scheme and moment diagram. ................................ ................................ ............. 93 4 3 Loading scheme for the measurement of elastic modulus in compression, with the use of extensometers. ................................ ................................ ................................ ......... 93 4 4 Comparison of methods used to obtain compression elastic modulus for concrete. This plot depicts three day samples. ................................ ................................ .................. 94 4 5 Typical plot of 1 day stress ................................ ................................ ................................ 95 4 6 Typical plot of 3 day stress ................................ ................................ ................................ 96 5 1 Set up of the transient state calorimeter. ................................ ................................ .......... 124 5 2 Extrapolation technique to acquire the temperature change of the concrete. .................. 125 5 3 Set up of the insulated calorimeter. ................................ ................................ .................. 125 5 4 Average temperatures (C) for the point of 622 seconds. ................................ ................ 126 5 5 Average temperatures (C) for the point of 623 seconds. ................................ ................ 127 5 6 The specific heat is obtained by averaging the final five values that were obtained by using t he moving average method. ................................ ................................ .................. 128

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10 5 7 Typical extrapolation technique used for the transient test, in order to obtain T2. ....... 129 5 8 Moving average for a 7 day cement paste sample. ................................ .......................... 129 5 9 Typical curves depicting the establishment of thermo equili brium within the flask calorimeter, in using concrete specimens. ................................ ................................ ....... 130 5 10 The evolution of concrete specific heat with age, in using the moving average method. ................................ ................................ ................................ ............................. 130 5 11 Hydration sketch of microdiffusion of free water through layers of already formed hydrates to unhydrated cement. ................................ ................................ ....................... 131 5 12 Typical curves depicting the establishment of equilibrium for the paste samples within the flask calorimeter. ................................ ................................ ............................ 131 5 13 The evolution of cement paste specific heat with age, in using the moving average analysis method. ................................ ................................ ................................ ............... 132 5 14 Curves depicting the establishment of thermo equilibrium for lime rock within the flask calorimeter. ................................ ................................ ................................ .............. 132 5 15 The results obtained from 5 individual specific heat runs for lime rock. ........................ 133

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11 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Engineering THE DEVELOPMENT OF THERMAL AND MECHANICAL PROPERTIES FOR MASS CONCRETE By Samuel J. Smith December 2007 Chair: Bjorn Birgisson Major: Civil Engineering Our study was aimed at contributing to the development of design parameters f or mass concrete. It consisted of the assessment, procedural development, and testing for mechanical and thermal properties that are relevant to the cracking of mass concrete at early ages. With this assessment, it was chosen to develop the methodology beh ind testing for the elastic modulus, modulus of rupture, tensile strain capacity, and specific heat. In addition to concluding on the The flexural test that wa s developed for early age concrete utilized third point loading with surface mounted strain gages. The tensile strength and elastic modulus in tension and compression increased, and the tensile strain capacity decreased from 1 to 3 day tests. The elastic m odulus of the compression region in the beam compared well to the estimated elastic modulus from the compressive strength using the equation indicated in ACI 8.5.1 2002, and the measured elastic modulus from compression cylinders. The tensile elastic modul i were generally lower than the elastic moduli in compression and is thought to be due to micro cracking within the tension region at an early stage in the loading process. The observed difference between the measured strains in the tensile zone versus the compressive zone warrants further investigation into this area.

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12 The specific heat of early age concrete and its components were measured with the use of an insulated dewar flask. The lime rock, cement paste, and concrete were adequately measured using the 11 value moving average analysis. The concrete and cement paste specific heat increased with age, and is thought to be due to the diffusion of excess water into the pore structure where the cement has previously undergone hydration. While the lime rock wo rked well for the insulated flask test, higher variability was obtained for the sand samples due to it requiring less mass and a longer duration of equilibrium time.

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13 CHAPTER 1 INTRODUCTION 1.1 Problem Description Mass concrete has been defined as an eleme nt having dimensions large enough to raise concerns with respect to the heats of hydration, which cause significant volume changes and therefore cracking within the structure. Although there are several methods that have been developed in order to assess t he vulnerability for a mass concrete structure to crack, there are few on a finite scale. The goal for this research was to work on the first step of developing this comprehensive model, which included a thorough literature review and the development of a specific heat and flexural test that could be used for early age concrete and its components. The literature review, which covers a broader base than the experi mentation that was conducted in this research, was aimed at developing an approach to solve this problem by including the study of various thermal and mechanical properties that are relevant to the cracking of concrete at an early age. The reason for the development of these tests is to use them to quantify properties individually, and to later integrate them into a finite element program to predict the onset of detrimental cracking. Other essential parameters that were identified and studied, but were not tested for include autogenous shrinkage, coefficient of thermal expansion, thermal diffusivity, and heat production (from a calorimeter). All of these properties are essential in the development of this finite element program because they encompass the ge neration and movement of heat, and how it is associated with the mechanical behavior.

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14 The mechanical behavior which raises concern with respect to mass concrete is cracking. The concrete will crack when the tensile stress exceeds the tensile strength. Thes e stresses may be induced by humidity and temperature factors, as indicated in Equation 1 1. (1 1 ) In this equation, st is the strain due to temperature and sh is the strain due to capillary shrinkage. In addition, the creep strain, cr reduces the overall stress accordingly (Figure 1 1). The temperature and relative humidity gradients that develop within mass concret e are the main factors that cause cracking. The following two cases introduce the fundamental issues that are associated with these factors. 1.2 Fully Insulated Case Regions of concrete in its elastic state may expand or contract due to temperature and rel ative humidity. Generally, a homogenous state of humidity and temperature within concrete does not induce strain, unless there are obstructions within or outside of the mass causing restraining forces against a uniform expansion or contraction. In order to achieve nearly homogenous relative humidity and temperatures (and therefore minimum strain), insulation may be used to prevent heat and moisture losses. In the case where a concrete block is fully insulated (and externally unrestrained), as in Figure 1 2 and 1 3, temperature and humidity gradients are nearly eliminated. However, this may not completely dismiss cracking, as humidity related strain may become an issue (Figure 1 3) Autogenous shrinkage may be a harmful mechanism, and is a result of the hydra ting cement paste consuming the water within the concrete matrix. Although the figures included in this chapter summarize the potential consequences in mass concrete, they may be studied in much more depth in Chapter 3, Literature Review.

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15 In the insulated case, there is only a slight temperature differential that develops within the mass, as depicted in Figure 1 4. Although this is one of the most effective ways of reducing the risks of thermal cracking, it has been found that especially when using high ea rly strength concrete, there may be too much heat produced at an early age. This may cause a couple of potential conflicts, including the formation of delayed ettringite (at a later stage) or a weaker concrete matrix of dicalcium silicate hydrate (immedi ately after hydration). With respect to autogenous shrinkage, regions will contract due to their porous nature and relative humidity (RH), as the water in a concrete mixture reacts with the Portland cement. The capillary stresses that may be experienced b y a region within an insulated mass concrete block may be brought about by autogenous shrinkage gradients, as indicated in Figure 1 3 and 1 5. The RH is simply the partial water vapor pressure divided by the saturation water pressure, as shown in E quation 1 2 It will adjust due to either a change in the partial pressure of vapor, or a change in temperature (which causes a change in the saturation vapor pressure). ( 1 2) The Kelvin equation, that describes the change of vapor pressure over a liquid curved with a radius r (such as in a capillary) may be written as follows, (1 3) where is the surface tension ; V m the molar volume ; R the u niversal gas constant ; r the radius of the droplet; and T the temperature By equating the Kelvin and Laplace equations and substituting RH of Equation 1 2 into Equation 1 3, we can calculate capill ary tension as depicted in Equation 1 4.

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16 (1 4 ) 1.3 Non Insulated Case In the case where insulation is not used on one face, the differential rela tive humidity and temperature between regions is more pronounced and may cause cases of conflicting expansion and contraction, and therefore strain. It is when these regions hold different conditions with respect to temperature and humidity that a coupling of the behavior may lead to the most ominous of stresses. If we were to look at one particular region, say region 3 of Figure 1 6 and 1 7, the total strain of this region is that which is induced by both temperature and humidity. In the case depicted in F igure 1 7, the relative humidity of the air is at much less than 100 %, and therefore encourages drying shrinkage. In the case where the concrete is kept at 100% relative humidity, the effect of relative humidity restraint may often times be considered neg ligible, as long as autogenous shrinkage is not significant. The thermal behaviors of concern within mass concrete include both heat movement, and heat production. As Figure 1 from the concrete equation, (1 5) where Q is the amount of heat transferred, t is the time taken, k is the material's conductivity S is the surface thr ough which the heat is flowing, and T is the temperature. The heat production within the mass is a property that may be measured with the use of a calorimeter, where the temperature is measured with respect to time within a concrete or paste

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17 sample of know n mass. The reaction of cement and water is exothermic, and therefore is accelerated with the addition of heat (Figure 1 8). used to describe the stress induced on the capillary matrix, but also the tendency for the moisture to migrate or evaporate. As the relative humidity of the surrounding air becomes less, there is more of a tendency for moisture on the face of the specimen to evaporate. In addition to this, as seen in Figure 1 9, moisture may be inclined to move from the central region towards the outer region if it is able to migrate through the capillary network within the concrete. 1.4 Tests Developed The main objectives of this research were to develop a flexur al and specific heat test. may be applied to early age concrete. A methodology was developed for both tests, so that the procedures may be applied to concrete at an early age. 1.4.1 Specific Heat to raise one gram of substance one degree of temperature. It is important because if the heat production of the concrete (in unit s of energy) is known within a massive structure, than the temperature rise within can also be calculated. Another thermal property that should not be confused with specific heat is the thermal diffusivity of a material. The thermal diffusivity describes t he speed that a heat front may move through a material. Together, these two properties can be used to calculate the thermal conductivity of a material by the following equation,

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18 Where is the thermal conductivity, c is the specific heat, and a is the thermal diffusivity. Therefore, the specific heat is the first step in calculating the thermal movement within mass concrete. ific heat evolved with respect to age (De Schutter and Taerwe, 1995). This is thought to be caused by the chemical reaction between cement and water. As concrete ages, new products are formed and therefore contribute to properties that evolve with time. Th e experiments conducted in this research were aimed at looking into the evolution of this property, as the concrete aged. In order to measure the specific heat, two separate calorimeters were developed. Within each calorimeter included a stir paddle, a hea ter, and two thermocouples. The stir paddle was used so that equilibrium could be achieved within. This was necessary because the specific heat is based on the amount of energy it takes to raise the temperature of a substance one degree. Therefore, by meas uring the heat energy outputted, this could only be related to the specific heat if it was assumed that all of the components within the calorimeter achieved equal temperatures. tts as a function of time. A numerical method could then be used to calculate the energy in kilojoules. The two thermocouples within the calorimeter were read by a portable data acquisition system. Both the energy measurements and thermocouple readings cou ld be uploaded and analyzed in excel. The two calorimeters that were developed included one that was based on work done by De Schutter and Taerwe, 1995, (a transient temperature analysis) and another one that was developed by the researcher (an insulated analysis). The transient experiment utilized two baths, where one was placed within another (Figure 1 10). The exterior bath was of the circulatory type, and was set to maintain a constant temperature of 28C, which was that of the room

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19 temperature within the lab. The interior bath was made from stainless steel and contained all of the components as indicated in Figure 1 10. During and after heat was supplied to the interior transient state of heat loss was analyzed and the specific heat was ultimately calculated, as will be discussed further in Chapter 5. The insulated test included the use of a high vacuum (10 7 torr) dewar flask, as indicated in the schematic of Figure 1 1 1. This procedure was developed in order to contain all of the heat added to the calorimeter. It also served to better observe the thermal equilibrium of the components within the flask, as this was not as clear as with the transient state of the previous experiment. As Figure 1 11 indicates, the setup within the insulated calorimeter is identical to heat, both a calibration test and material test were n eeded for each experiment. This will also be described in more detail in Chapter 5. 1.4.2 Flexural Test The development of a test that can accurately indicate the mechanical behaviors of mass concrete is a critical contribution to modeling it on a finite s cale. Unlike the specific heat tests, which measure a single thermal property, the flexural test is used to measure three critical properties. These include the modulus of rupture (MOR), tensile strain capacity, and elastic modulus in tension and compressi on. While the MOR estimates the stress at which concrete may fail in tension, the tensile strain capacity is defined as the strain at which concrete will fail. Furthermore, the elastic modulus is a property that is indicated by the amount of stress that a material undergoes with a unit strain applied. While mass concrete may often times contain thermocouples, these temperatures may be used to ultimately indicate the thermo mechanical movement of mass concrete. While the

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20 expansion or contraction can be calc ulated with the coefficient of thermal expansion, the tensile strain capacity may be used to check the status of a certain region. The elastic modulus can also be used to indicate what the stress state is for a given strain. Like the specific heat test, t he flexural test needed to be compatible with early age concrete, and additionally it needed to be applied in order to study changes in mechanical properties at different ages. It was decided that the third point loading scheme would be used for this proj ect. This included capturing the magnitude of load with a load cell, and the magnitude of stain with two strain gauges. One strain gauge was placed on the top surface and the other on the bottom surface, in order to measure compressive and tensile strain, respectively. The stress versus strain relationship was used to obtain the elastic modulus in tension and compression by calculating the slope of the initial linear portion of this graph. Efficiently, four important properties were obtained from this tes t. The loading scheme is indicated in Figure 1 12. 1.5 Main Objectives of Study The main objectives of our study included the development of a mechanical and thermal property test for early age concrete. More specifically, this includes the following: The evaluation of the use of a beam test for the determination of tensile strength, elastic modulus, and tensile strain capacity of concrete at an early age. The evaluation of test methods for the determination of specific heat of early age concrete. 1.6 Scope of Work The scope of work performed in this study includes the following: Survey of specifications A review of various department of transportation and government agency guidelines and specifications involving mass concrete. Literature review. Performan ce and evaluation of compression and flexure test.

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21 Evaluation of specific heat test and conduction of test on aggregates, cement paste, and concrete. Figure 1 1. Graphical depiction of stress exceeding the strength within a certain region of mass concrete.

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22 Figure 1 2. Temperature effects on fully insulated mass concrete. Figure 1 3. Relative humidity effects on fully insulated mass concrete.

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23 Figure 1 4. Depiction of heat flow in an insulated case. Figure 1 5. Depiction of moisture state in an insulated case.

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24 Figure 1 6. Temperature effects on non insulated mass con crete in one dimension. Figure 1 7. Relative humidity effects on non insulated mass concrete in one dimension.

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25 Figure 1 8. Depiction of heat flow in a non insulated case. Figure 1 9. Depiction of moisture flow in a non insulated case.

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26 Figure 1 10. Set up of the transient state calorimeter. Figure 1 11. Set up of the insulated calorimeter.

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27 Figur e 1 12. Loading scheme for the third point beam test, and accompanying moment diagram.

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28 CHAPTER 2 SURVEY OF SPECIFICAT IONS 2.1 Introduction dimensions large enough to re quire that measures be taken to cope with the generation of heat definition was made to be ambiguous because there are infinite combinations of mix designs, geometries, a nd ambient conditions that may lead to cracking in mass concrete. However, most states have set their own guidelines that classify mass concrete as having minimum dimensions at or above a certain threshold, usually in the range from 4 to 5ft. Unites States agencies, such as the Army Corps of Engineers and the Bureau of Reclamation also have guidelines and perform their own experimentation to determine certain parameters to follow. 2.2 State Specifications There were seven states that were surveyed by observ ing their current mass concrete specifications and provisions. These states included California, Colorado, Delaware, Florida, Iowa, Virginia, and West Virginia. All of these states had specifications addressing several important requirements for the constr uction and engineering procedures involving mass concrete. The regulated parameters included allowable temperature gradients, allowable peak temperatures, and limits involving mineral admixtures. The specifications also included a description of what it is that constitutes mass concrete and construction procedures that need to be followed during the curing process. considered mass concrete, and actions are taken in order to re duce both the temperature gradient and peak temperature in accordance with the state specifications. A specialty engineer is often

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29 hired by the contractor to decide on a safe temperature range, to design the mix, and also to help monitor the temperatures. Typically, the monitoring program involves putting at least two sets of interior and exterior temperature probes (e.g. thermocouples) within each mass concrete element. Generally, the most practical way to limit temperatures includes the replacement of Po rtland cement with fly ash or ground blast furnace slag. The measures taken to reduce the temperature magnitude and gradient are discussed in more detail in the literature review. Although the specialty engineer often has a good idea about the most effecti ve mix design, some states specifically indicate certain limits on mineral admixtures. Some specifications may be ambiguous, due to them only mentioning a maximum amount of admixture, but not specifying a recommended range. It is evident in Table 2 2 that there are various ranges or specified maximum amounts of admixtures to replace cement with. This is partly attributed to the variability in admixture properties when obtaining the product from different locations. In fact, te that multiple sources of the same type of pozzolanic material are not permitted within the same structure. For some mass concrete structures, additional effort must be made in order to limit thermal cracking. Mentioned by the Delaware specifications, t he use of insulated forms and curing blankets help there to be a uniform distribution of temperature. One method of reducing the temperature magnitude involves using cooling pipes within the mass during the hydration period. California Transportation Depar tment mentions this technique for use in the more massive applications, but requires that the pipes must be fully grouted after the cooling is completed. Cracks may occur in massive structures, either due to the negligence of the contractor, or because of

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30 to resist the ingression of deleterious elements that may be a precursor to structural failure. Another important reason for epoxy injection is to beautify the appearance of portions of the structure that can be viewed by the public. As the Virginia specif ications mention, it is also important for the excess mastic compound to be removed and for the surface to be made visually uniform. In cases where the cracks are more extreme due to the contractor exceeding the temperature control requirements, then the c ontractor may be ordered to remove and replace the concrete at no additional cost to the project. It can be seen in Table 2 around 160 F. This temperature is chosen due to extensive research that has found delayed ettringite formation (DEF) to occur after concrete has been subjected to temperatures around 175 F (Nasser and Lohtia 1971, Ramlochan 2003, Ramlochan 2004). At times, a rathe r large deduction in pay will be implemented against the contractor if the specified limit in temperature is exceeded. For example, the mass concrete specifications for a bridge in Colorado (project number HB 0821 075, Apr. 28, 2005) indicated that if the temperature of concrete exceeded 11 F or more above 165 F, then the bid price for concrete would be deducted by $200.00 per cubic yard of concrete. The fines were reduced for temperatures that were less above the maximum, starting at a deduction of $3.00 per cubic yard for temperatures fr om 0 4 F above the limit. With respect to temperature differential, it is not an issue of chemical consequences, but rather one of conflicting mechanical behavior of regions within the mass. Caused by a non uniform temperature profile, conflicting mechani cal behavior occurs due to variations in thermal 1 refers to the maximum difference in

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31 temperature allowed between the hottest and coolest temperature monitoring probe taken from a section. These values a re based on experimental and field data where it was found that a certain magnitude of temperature differential caused cracking comprehensive (see Table 2 1), in that the maximum allowable temperature difference was highe r as the concrete became more mature. 2.3 Government Agencies 2.3.1 U.S. Army Corps of Engineers The U.S. Army Corps of Engineers is responsible for various civil engineering projects in uction of military facilities for the Army and Airforce. In addition to this, they also design and operate water resource and civil work projects. As a result, they have designated their own guidelines that are somewhat fications. Their guidelines include special provisions discussed by ACI Committee 207 (2005) in order to counteract thermal cracking. The following list describes what additional measures are taken in mass concrete, when compared to the construction proced ures of non massive concrete: Changing construction procedures, including placing times and temperatures. Changing concrete materials and thermal properties. Pre cooling of concrete materials and controls on concrete placement temperature. Post cooling of concrete. Construction of joints (with waterstops where necessary) to control location of cracks. Alteration of structure geometry to avoid or control cracking. Use and careful removal of insulation There are three levels of analyses that are used by the U.S. Army Corps (U.S. Army Corps 1997) when designing a structure that is potentially considered massive. In order to assess the vulnerability of cracking for a mass concrete structure (MCS), level one analysis is used to make a conservative guess and to d etermine if a more detailed analysis is necessary. It involves little or

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32 no laboratory testing and assumes the worst reasonable combination of material properties and site conditions. Strain, length change, and cracking are computed based on temperature ch ange in the MCS. In addition, an assumption of complete restraint of thermal expansion is made. For the level two analysis, thermal analysis is based on a more rigorous determination of concrete temperature history by the use of several analysis tools. The temperature history of concrete may be estimated by the use of 2 D (cross section) or 1 D (strip) finite element analysis, or Schmidt and Carlson methods. An evaluation of the cracking involved within the interior as well as the cracking at the surface is evaluated at this level. Level three analysis involves detailed cracking evaluation of complex shapes and loading conditions other than thermal loads. Usually performed exclusively with the finite element method, efforts is first put forth in order to col lect environmental data, assess and implement applicable construction parameters, and perform the testing required for thermal and nonlinear material property input. This analysis involves a 3 D finite element model, and requires much more time than the ot her methods. 2.3.2 U.S. Bureau of Reclamation The U.S. Bureau of Reclamation is best known for the dams, power plants, and canals it constructed in the West. They constructed more than 600 dams, including the Hoover Dam on the Colorado River and the Grand Coulee Dam on the Columbia River. Due to their involvement in dam construction, their method of crack reduction emphasizes the use of cooling pipes. John Laboon, U.S. Bureau of Reclamation, was able to provide literature (Townsend 1981) that displayed the plans of the elaborate cooling system involved in the construction of the Glen Canyon Dam. Generally, it consisted of pipe or tubing placed in grid like coils over the entire top surface of each 5 or 7 foot lift of concrete. Aside from the embedded pipe cooling system,

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33 another method included reducing the placing temperature of concrete. Although the average recommended cooling temperature is 50F, it has been reported to be as high as 65F. The bureau also finds it important to evaluate the cracking on t he surface of mass structures, after they have been poured. Cracks that begin to raise concern include those that are more than 0.01 in. Similar to state guidelines, the bureau usually specifies that such cracking needs to be filled with a special epoxy ag ent. Table 2 1. Limiting conditions, indicated in mass concrete specifications taken from various State DOT Constitution of Mass Concrete Max Temp (Deg F) Max Differential (Deg F) West Virginia Min Dimension of 4ft. 160 35 Virginia Min Dimens ion of 5ft. 170 w/Slag, 160 w/FA. 35 Iowa Min Dimension of 3.9ft. 160 35 Florida Specified by specialty engineer. Specified by specialty Engineer. 35 Delaware Determined subjectively on a project to projec t basis. 160 48hrs = 40F, Next 2 7 Days = 50F, Next 8 14 Days = 60F. Colorado Min Dimension of 5ft. 165 45 California Min Dimension of 6.6ft. 160 Specified by the thermal control plan, provided by the contractor.

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34 Table 2 2. Required amounts of mineral admixtures, indicated in mass concrete specifications State Fly Ash Required (% Replacement of Cement) Slag Required (% Replacement of Cement) Required Mineral Admixture Replace ment Of Cement (%) Total Required Cementitious Material (lb/ft 3 ) WVA 25% (Max) 50% (Max) 50% (Max) VA 25 40% 50 75% IA 35% 20.79 FL 18 50% 50 70% DEL 75% (Max) 75% (Max) CO CA 18.73

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35 CHAPTER 3 LITERATU RE REVIEW 3.1 Overview of Issues with Mass Concrete As more foundations and dams were poured from concrete in the United States during the twentieth century, much attention was directed towards mass concrete, and the problems associated with it. The compli cations corresponding with mass concrete included excessive cracking thought to be brought on by high temperatures. This speculation led to several studies during this time, in order to pinpoint the issues. Mead (1963) presented a data analysis of Pine Fla t Dam, where the temperatures were monitored within and between successively poured lifts. When this dam was constructed, it was decided that it would not only serve as a retention structure, but also as a study to determine the effects that the hydration, geometry, and environment have on the heats produced within mass concrete. Electrical resistance thermometers were embedded throughout, and were able to illustrate temperature profiles. The dam was poured in lifts in order to allow the concrete to cool in increments and therefore not produce high temperatures in concentrated areas (Figure 3 1). It should be noted how the differential temperatures peak at a certain time, and then converge to zero. Figure 3 2 shows the typical temperature profile between s uccessive lifts, where at least a 5 day curing period takes place before each proceeding lift placement. It can be noticed that the initialization of each successive lift causes the preceding lift to fluctuate in terms of temperature. The hypothesis made b y these researchers was that cracking would be present where the monitored thermal gradients would reach excessive values. At the time of this publication, it was Figure 3 1 it can b e seen that the internal gradient does not exceed 10 F in this lift, and as a result there was no

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36 cracking depicted in this lift at early ages. With the specifications of today, one may have been able to say that this differential is in fact safe for the concrete. In the years to come, more research was conducted, and it was confirmed that thermal gradients due to the heats of hydration cause cracking in mass concrete (Burg and Ost 1994, Burg and Fiorato 1999, Faria 2006, Kim et al. 2002, De Schutter and T aerwe 1995). The conclusions brought about by these studies were derived from experiments which utilized more enhanced instrumentation, microscopy, and software tools. In addition to this, findings from researchers with respect to the degree of hydration o f concrete and associated heat flux, as De Schutter and Taerwe (1995) found, helped to lead to accurate models which could be used to predict the temperature profiles and stresses in later work (De Schutter 2002). Ballim (2003) successfully implemented a f inite difference model in order to predict the temperature curve at different locations within mass concrete, as this will be discussed in more detail later. In addition to thermal gradients, relative humidity gradients and high temperature curing have also been found to pose detrimental effects on concrete. Mechanically, humidity gradients may act similarly to thermal gradients in order to cause differential contraction and ultimately lead to cracking (Grasley 2003, Bentz and Jenson 2004, Lee et al. 20 06, Ulm and Coussy 1995). In contrast to the effects of gradients, high temperature curing may cause alternative chemical reactions to take place, creating compounds which are inferior to those produced at more moderate temperatures (Nasser and Lohtia 1971 Mindess et al. 2003, Ramlochan et al. 2003, Ramlochan et al. 2004). 3.2 Heats of Hydration The hydration of Portland cement is an exotherm ic reaction which may produce temperature rises as high as 50 C in mass concrete It consists of combining the comp ounds of Portland cement with water and producing hydration products. Because the reaction is

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37 temperature dependant, the climbing temperature accelerates the reaction and the concrete may set at even hotter temperatures than expected. Ulm and Coussy (1995) suggest that a s the reactions proceed, the water diffuses through the cement from the regions of the hydrated cement to the regions of unhydrated cement where products form on an instantaneous manner, relative to the timescale of the diffusion process. W ith respect to reaction kinetics, the diffusion of water is said to be the most dominating mechanism of the hydration reaction (Ulm and Coussy 1995). The hydration reactants consist of compounds within the cement which react at different rates, release di fferent amounts of heat, and contribute differently to strength (Table 3 1) I t should be noted that the C 3 A + CSH 2 as well as the C 3 liberation. 3.2.1 Temperature Prediction in Mass Concrete Ballim (2003) develop ed a two dimensional finite difference model to predict the fluctuation of temperature with respect to time. His predictions were found to be within 2 C of actual temperatures. Like Ulm, Ballim knew that an important problem facing heat modeling is that t he rate of heat evolution in a specific element depends on mixture parameters, time, and position within the mass. After determining the rate of heat liberation of the material by use of a calorimeter, the Arrhenius maturity function was used to predict th e rate and extent of hydration at any time and position within a block which was 700 x 700 x 1000mm. dimensional flow of heat (the third dimension being insulated) as well as the maturity of concrete with respect to time. The heat flow within a porous medium may be described by the Fourier equation, (3 1)

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38 where is the density of concrete ; Cp, the specific heat c apacit y; T, the temp erature; t, the time; k, the thermal conductivity; x and y, the coordinates the rate of internal heat evolution. total heat Q from calorimeter tests, noted as the following: (3 2) where m is the mass of the sample and T is the change in temperature of the sample over the time period under consideration. The rate of heat evolution is therefore derived as the following: (3 3) However, Ballim (2003) realized that although Equation 3 2 factored in the temperature change, its derivative in Equation 3 3, does not account for the effect which temperature magnitude has on the rate of the reaction (ie., the production of heat). Therefore, it is essential to adjust for this factor, as the temperature magnitude is constantly changing and affecting the reaction rate of the medium. In order to predict the heat liberation accurately, one needs to express the heat rate equation in terms of the maturity time rather than real time. Therefore, the Equation 3 4 expresses the maturity based heat rate which is used to account for the exothermic nature of the reaction. (3 4) The heat rate equation in terms of real time is needed in order to calculate the flow of heat, as indicative of Equation 3 1. It is derived by using the chain rule and is noted as the following: (3 5)

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39 Arrhenius relationship. It is cruc ial to find the change in heat with respect to maturity time, in order to accurately depict the rate of heat liberation at individual time frames. The following equation depicts the Arrhenius relationship. (3 6) In this equation, t 20 is the time required when curing at 20 C to reach equivalent maturity of an insitu element. T i is the average concrete temperature (K) in the time interval t i T 0 is the reference temperature (taken as 20 C ). By using the Arrhenius relationship, one is able to calculate the effective maturity of the concrete and apply this value to the time based heat data re ceived from the calorimeter i n order to i ndicate the rate of h eat liberation by Equation 3 4 and 3 5 above. When situations arise where there will not be significant thermal gradients or extreme temperatures, than the heats of liberation are usually not of concern. However, how should we different state specifications for what is considered mass concrete. This is because there are many factors which contribute to heat production, including ambient temperature, mixing temperature, and cement type variability. Bamsforth (1984) specifies that for sections in excess of 2m (6.6ft), temperature rise is directly proportional to the cement content. He had also noted that the heats from hydration in mass concrete become increasingly an issue when the cement content is greater than 350kg/m 3 (22 lbs/ft 3 ). However, as high strength concrete has become more utilized in recent years, it has raised further concerns, due to its propensity to producing more h eat than normal strength concrete. This has also led to increased uncertainty of the

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40 dimensional thresholds set by the states, due to higher temperatures leading to problems at smaller dimensions. Bamsforth (1984) mentions that for a section that is less t han 500mm thick, it is usually assumed that heat is readily lost to the environment and does not cause significant internal thermal restraints. Ulm and Coussy (2001), on the other hand indicate that the hydration heat diffusion length may be determined in order to decide whether or not a structure should be considered massive. The following equation depicts his theory on the gauge length, l h (3 7) where D is the thermal diffusivity and h is the characteristic hydration time. The value h is considered intrinsic to the material (respectively to the mix proportions of the material). In Ulm length where the latent hydration heat affects th e long term structural integrity for high performance concrete is when l h = 0.2m, while in normal strength concrete, l h = 0.3m 3.2.2 Low Heat Cements In order to account for the large amounts of heat generated within massive structures where high strengt h concrete was not needed, Type IV cement was developed in order to lessen the heat production. Type IV cement is produced with less C 3 A and C 3 S, in order to relieve the concrete from arduous stresses brought on by large amounts of heat (Mindess et al. 200 3). However, it was found that by only reducing the amount of C 3 A content (and not as much C 3 S) and fine adjusting the other components accordingly, it poses as an effective and efficient solution. Less C 3 A content not only produces a lower adiabatic tempe rature rise during hydration, but also produces higher sulfate resistance. While lowering the C 3 S amount may have a similar impact on heat generation, the high early strength of concrete can be reduced substantially (Mindess et al. 2003). In considering th e types of Portland cement to be used, it can be found that Type IV

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41 cement (Low Heat of Hydration), which has a considerably low C 3 S content, is nearly extinct C 3 S available for early strength. It should be noted that a lower rate of hydration is the key to less heat generation. Therefore, another efficient way to de crease the heat produced during the hydration process is by replacing some of the Portland cement with mineral admixtures, which hydrate at a slower rate, and ultimately contribute to lower peak temperatures within a curing mass. The most popular mineral a dmixtures include ground blast furnace slag and fly ash. 3.2.3 Mineral Admixtures In common practice, m ineral admixtures may be used to either replace cement, improve the workability of concrete, or to enhance the durability of concrete When dealing with mass concrete, mineral admixtures are often used for the same reasons, and especially for replacing the cement content. Replacing cement with mineral admixtures that hydrate at a much slower rate yields much less heat and also produces a denser and more ti ghtly bound matrix (Malhorta and Mehta 1996, Naik et al 1994, and Wee et al. 2000). Heat generation is dependent upon mineral admixtures (as well as minimum dimension) in OPC concretes (Bamsforth 1984), as shown in Figure 3 3 and Figure 3 4. Notice that it is typically acceptable that larger amounts of Blast Furnace Slag (BFS), rather than Fly Ash, may customarily be used to replace cement. Unlike Fly Ash, BFS is a cementitious admixture, which means that it only needs water to react. Fly Ash however, needs a combination of water and calcium hydroxide (from cement paste), in order to produce calcium silicate hydrate. The weakness of mineral admixtures is that the strength gain is

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42 3.2.4 Other Methods to Lessen Heat Other effects on heat generation include the pour size, the type of formwork, and the mixing temp. In Figure 3 3 and Figure 3 4 the temperature rise with respect to minimum dimension can also be seen. As it can be depi cted in the graphs, the largest increase in temperature rise occurs when the minimum depths range from 0.5m 2m in OPC concrete (the curves are the flattest in this region). Pours that have a minimum dimension which is greater than 3 m to 4 m asymptotical ly reach a maximum temperature increase, which depends on the admixture replacement percentage. This asymptote is due to the concrete nearly having full insulation within itself at these higher dimensions. The type of formwork or the use of insulation may also be a significant factor in controlling the liberation of heat in a mass pour, but several factors should be accounted for with respect to this. Plywood happens to have much better insulation properties than metal forms and therefore may be able to ser ve as an insulator and lessen the changes in temperature from the core to the exterior. Although forms may serve to moderate the temperature differential, it is also important to consider the overall rise in temperature (Bamsforth 1984). By heavily insulat ing concrete, it may result in the deterioration of the hydrated cement paste (HCP) properties at high temperature (Ramlochan et al. 2003, Ramlochan et al. 2004). Thermal shock also needs to be considered as these forms are removed, and the newly exposed s urfaces cool to the surrounding temperature. For the face of concrete which is exposed to the air, several types of insulation can be used to lessen thermal gradients. Wetted quilts or burlap can not only serve as insulators but also provide the concrete w ith essential moist curing conditions (Bamsforth 1984). Another method is to use tenting, in order to prevent evaporative cooling. Tents are especially useful when the open air has a relatively small amount of water content at a given temperature. This is known as relative humidity, and when it is low it may cause deleterious evaporative cooling and

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43 loss of water at the surface (Grasely 2003). Other forms of insulation include foam mats, soft board, or sand laid on polythene sheets (Bamsforth 1984). The mi xing temperature is another factor that may lower the heats of hydration. By cooling the mixing temperature, the heats generated during critical hydration periods are less. This can be accomplished by using chilled water, ice, or cooled aggregates within t he mix. Cracking may still occur, even though insulation or plywood formwork is used, or the that reason, the predominant way to solve the problems of heat lib eration lies in cement chemistry and the nature of exothermic reactions. 3.3 Cracking Cracking is one of the main concerns when considering the durability of concrete. It allows ions to access the matrix with much less impedance and may lead to increased c orrosion of the steel reinforcement, more prevalent sulfate attack, and ultimately more vulnerability to structural failure. As will be discussed shortly, the internal restraint of concrete is a cause for cracking, and can be a result of temperature or rel ative humidity differences within its mass. These restraints are what cause significant strains to develop because of the conflicting contraction rates. However, the strains are not harmful unless they cause significant magnitudes of cracking. The magnitu de of cracking is determined by the thermal expansion coefficient of concrete, the degree of restraint and the tensile strain capacity (Bamsforth 1984, Houghton 1976). According to Bamsforth (1984), there are several practical ways to reduce the likelihood of cracking within high volume pours, including the following: Reduce the peak temperature during curing Select aggregate with a low thermal expansion coefficient Minimize the restraint to thermal movement Increase the tensile strain capacity

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44 Reducing the peak temperature usually moderates the differential temperatures within the concrete and the overall temperature fall to ambient conditions. The overall fall of the mass is xternal restraint. For this reason, the peak temperature is one of the most important attributes to control with respect to thermal stresses. During the construction of the Pine Flat Dam (Mead 1963), one of the control measures taken in order to reduce the peak temperature was to keep the concrete cool before and during the pour. In fact, there was a limitation set that the concrete had to be from 40 F to 50 F while being placed. The way that they chilled the mix included screening the aggregates with cool well water and refrigerating the other ingredients, except for the Portland cement. The target temperature of the cooled components was at 35 F. When the ingredients all came together as the concrete was being mixed, flake ice was added as well. Another wa y to reduce cracking may be by selecting an aggregate with favorable mechanical and thermal properties. In the case where an aggregate with a low thermal expansion coefficient is used, the concrete matrix will be subject to much less strain when temperatur es rise and fall (Bamsforth 1984). Typically, aggregates with lower thermal coefficient values also have a higher strain capacity (Table 3 2). Therefore, although it is much weaker in strength than gravel or granite, using limestone may reduce the occurren ce of micro cracks in mass concrete due to it having a lower coefficient of thermal expansion and a higher tensile strain capacity. 3.4 Mechanical Effects of Temperature and Relative Humidity Gradients Through experience and laboratory studies, m any states have required that the temperature differential does not exceed a certain value in mass concrete ( See Survey of Specifications, Chapter 2 ) After it has developed some stiffness if the regions within are not moving (i.e., thermal movement) in unison with one another because of differences in temperature the regions

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45 act to resist the movement of one another The tensile stress that concrete encounters as a result of this is often referred to as restraint. Restraints may be classified as either internal or externa l (Bamsforth 1984). 3.4.1 Internal Restraints When the central region of a concrete pour is considerably hotter than the exterior regions, its tendency is to resist the cooling shrinkage of the latter. Because there is a shrinkage gradient that dev elops, cracking in the exterior region may occur as a result of this phenomenon, increasing the exposure to ominous ions such as sulfates or chlorides. On the other hand, a cooling core may cause internal cracks to form after it has hydrated as a conseque nce of a restraining outer shell (Houghton 1976, Mead 1963) Internal restraints are characterized by the strains that occur due to opposing forces of regions within a mass, as mentioned above. Although it is often overlooked by state specifications, diffe rential relative humidity may also be a cause for internal restraints (Grasely 2003, Bentz and Jenson 2004, Lee 2006, Ulm and Coussy 1995). Drying shrinkage may be one result from the air having a low relative humidity, causing capillary tension to develop in the pore structure (Bamsforth 1984, Grasely 2003, Ulm and Coussy 1995) Therefore, as a result of both relative humidity and temperature being non uniform throughout, differential movement occurs, and depending on its degree may cause cracking However relative humidities are often not monitored due to the humidity sensors either being unreliable or extremely expensive. Work from Ulm and Coussy (1995) presented a theoretical and mathematical coupling of both the effects from temperature and relative hu midity. Some years later, Ulm and Coussy (2001), worked to develop a finite element model, which was used to predict cracking based on the unique concept of the hydration heat diffusion length (mentioned previously). Also, this work and another publication Faria et al. (2006) ind icate that the heat production, flow of heat, and

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46 flow of moisture may be treated independently from the mechanical movement. For example, they assumed that the formation of a small crack would not effect the movement of heat or m oisture through the concrete. This assumption seems to be valid, when one is to consider the size of these cracks (very small) in relation to the size of the concrete in question. 3.4.2 External Restraints External restraints are those that may be imposed on mass concrete by its immediate surrounding environment or an adjacent structure. Situations may involve ground rock imposing restraint onto drilled shafts which undergo expansion or contraction throughout the hydration process. Another example may invo lve a rigid foundation restricting the thermal movement of a wall cast onto it. The magnitude of external restraint is directly related to the net amount of expansion or contraction on a macroscopic scale, and the force that the surroundings impose in orde r to prevent this expansion or contraction from occurring (Bamsforth 1984). In the study of Pine Flat Dam ( Figure 3 2), external restraints were a concern as layers (lifts) of the dam were poured in increments of at least five days. The critical region of concern with external restraint is usually the interface of the two bodies in question (Mead 1963). In this region, tensile and shear stresses may cause cracking, especially in the newly poured concrete, where the maturity is not as developed. 3.4.3 Tempe rature Related Restraint While internal restraints are usually governed by guidelines (maximum tempe rature differentials) set by state specifications, external restraints are usually controlled by the subjective issue s. Internal restraints are usually of more concern due to the frequency of cracks resulting from them and their associated complexity. Therefore, one will find that the majority of literature written on mass concrete cracking has to do with the internal re straints.

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47 In general, three factors have been found to govern the uniformity of temperature within concrete during its early ages, namely: S urface area to volume ratio Rate of hydration Amount of insulation used The surface area to volume ratio has been found to raise concern when values are less than 1 ft 1 This ratio is based on the same concept behind states defining mass concrete as having a minimum d imension at or above a certain value. The concept is that concrete usually dissipates most of its he at to the ambient air through its least dimension, and therefore the gradients and maximum temperatures are usually controlled by this parameter. For a given mass structure, the finalized design is given to the contractor, who usually becomes liable for it s sound construction with respect to material and dimension. Often times, contractors hire specialty engineers to consult with them on the mix design and precautions to take (including formwork), in order to produce a structure with as little cracking as p ossible. By knowing the thermal expansion coefficient and hydrating temperature range, the amount of rapid or slowly induced strain may be conservatively estimated with the use of the thermal expansion equation (Houghton 1976, U.S. Army Corps 1997), namel y, (3 8 ) contracting system, and did not account for the effect that a gradi ent of expansion or contraction had on the amount of strain encountered. This is similar to the Level 1 Analysis described by the Army Corps (1997). The advantage of the finite element analyses (FEA) that were conducted in more discretely accounted for stain gradients that developed in mass concrete. Although FEA may be used to depict temperatures and stresses throughout mass

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48 concrete in a detailed manner, some problems may be encountered. The problems included the difficul ty of predicting the mechanical or thermal properties as a function of the degree of hydration, or maturity. Ultimately, this led to inaccuracy in the prediction of stresses. Today, thermal stresses are usually obtained by FEA after determining the therma l distribution, which may also be obtained by FEA. Nakamura et al. (1999) designed a finite element model application to predict stresses that also accounted for the uncertainty in the material properties and environmental conditions. Their study used a fi rst order approximation theory based on Taylor expansion. De Schutter (2002) presented a study where he used his previous work in order to devise an element simulation for temperature and stress prediction in concrete. In his early work (De Shutter and Tae rwe, Cem. Concr. Res., 1995), he developed a general hydration model for both Portland cement and blast furnace slag cement. He also studied the specific heat and thermal diffusivity of concrete (De Shutter and Taerwe, Mag. Concr. Res., 1995) as a function of the degree of hydration. Another publication (De Shutter 1999) describes a degree of hydration based Kelvin model for the basic creep of early age concrete. These studies parameters would be better justified. Faria, et al (2006) developed a finite element program that accounted for the evolution of the thermal conductivity and activation energy as a function of the degree of hydration. For this application, the degree of h ydration was computed as the ratio between the heat released up to a certain instant, t, and the total heat expected. However, he made the assumption that specific heat ) study, where he found variations below 5% of its final value. He also assumed a constant value for the thermal expansion coefficient.

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49 Faria et. al (2006) also accounted for the evolution of the mechanical properties, including compression, tension, and e lastic modulus by the following equations (Rostasy et al. 2001): (3 9) (3 10) (3 11) Another method of measuring thermal stresses (Kim, et al., 2002), shown in Figure 3 5, involved something d ifferent from the recent FEM approach. Their study involved a frame device which was built to restrain the thermo mechanical movement of concrete. It was done by building the frame to dilate according to constraint material which had a different coefficien t of thermal expansion when compared to that of concrete. An important feature of this method was that the uncertain material properties of early age concrete such as the modulus of elasticity and coefficient of thermal expansion could be calculated throug h innovative mathematical relationships. This involved the stresses induced on the load cell as a result of the coupling mechanism between the constraint material and concrete. 3.4.4 Relative Humidity Related Restraint W ith respect to its internal relative humidity, mass c oncrete may either undergo autogenous or drying shrinkage. Faria (2006), indicates that Normal Strength Concrete (NSC) is usually more susceptible to drying shrinkage while High Strength Concrete (HSC) is more vulnerable to autogenous shri nkage. Faria also mentions that the affects which thermal gradients have far outweigh the effects of autogenous shrinkage in NSC. In addition to this, problems associated with drying shrinkage may simply be controlled by monitoring the relative humidity

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50 an d temperature of the exterior environment. For instance, Kim et al. (2002) ensured that the testing environment for his device was kept at a relative humidity at over 85%, to minimize drying shrinkage. 3.4.4.1 Autogenous shrinkage Autogenously, concrete ha s a tendency to shrink due to the products of concrete having less volume than the reactants (Bentz and Jenson 2004, Lee et al. 2006, Ulm and Coussy 1995). Autogenous shrinkage occurs by the concrete consuming the internal moisture through the chemical hyd ration process (i.e. developing small voids), and as a consequence creating capillary tension through the menisci of moisture within the pore structure. However, much like thermal movement, autogenous shrinkage does not occur uniformly throughout mass conc rete, due to it being dependant on the maturity, which is directly affected by the temperature (Ulm and Coussy 1995, Ballim 2003, Faria 2006). At later ages, the core region is prone to autogenous shrinkage and may be restrained by the outer vicinity, whic h has undergone drying shrinkage at an earlier age (Ballim 2003). As mentioned above, this becomes most significant when HSC is used. 3.4.4.2 Drying shrinkage Concrete may undergo drying shrinkage when it loses water due to evaporation (at a surface) to th e ambient surrounding air. As Kim et al. (2002) mentions, higher tensile strengths and elastic moduli are present in the interior portion of mass concrete at early ages due to there being more maturity when compared to the exterior portion. Therefore, the surface may prematurely undergo drying shrinkage as a result of capillary tension and in this case be more vulnerable to cracking. Some authors, such as Ulm and Coussy (1995), mention that evaporation may also lead to incomplete hydration of the exterior s urface. Others (Mindess et al. 2003), suggest that hydration may continue if water is later provided, however not to its full degree.

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51 3.4.4.3 Combinational effects With respect to both autogenous and drying effects, Equation 3 12 represents the capillary tension with respect to relative humidity (Grasley 2003). (3 12) In this equation, RH is the relative humidity, and R, T, and V m are the univer sal gas constant, temperature, and molar volume of water, respectively. Conceptually, the equation describes how the capillary tension is directly related to the evaporative potential of the water within the void spaces to become vapor. This potential ener gy exerts what is known to be the capillary tension within the micro voids of concrete, and conceptually applies to both drying and autogenous shrinkage. It can be seen in Figure 3 6 that theoretically there is nearly a linear relationship between capilla ry tension and internal relative humidity (Grasley 2003). The graph only shows a relative humidity range between 50 100% because when the relative humidity drops below 50%, the menisci are said to be unstable and other mechanisms are said to contribute to stresses. In summary, when considering the mechanical stresses that develop in mass concrete, one has to recognize both temperature and humidity differentials from the center to the exterior. As mentioned earlier, drying shrinkage may be accounted for by providing a controlled environment. Autogenous shrinkage may be assumed negligible in some circumstances using NSC, but needs to be accounted for when using HSC. 3.5 Chemical Effects of Extreme Temperature and R elative Humidity When considering the chemic al alterations of hydrated paste, careful attention should be made to individual temperature and humidity extremities that may alter the hydratio n products of concrete. If certain regions within a mass structure have in fact endured through a rigorous

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52 temp erature cycle with minimal cracking due to internal and external restraint, have their intrinsic properties been altered? Nasser and Lohtia (1971) found that the compressive strength and modulus of elasticity are both affected immediately after the exposur e to higher consequences of higher curing temperatures are not always immediately evident in some concretes. 3.5.1 Immediate Effects Nasser and Lohtia (1971) conduct ed an experiment that consisted of two main test groups of cylinders, Group A and B, which would be exposed to the same temperatures that included 35 F, 70 F (control), 160 F, 250 F, 300 F, 350 F, 400 F and 450 F. The only difference between the gr oups is that they were to be exposed starting at a different time after the cylinders were cast. Group A was exposed to these temperatures after one day of moist curing, while Group B was exposed after 14 days of moist curing. Within group A and B, the cyl inders were divided up so that at least three would be exposed to a particular constant temperature for a given time period, and then tested for ultimate strength and modulus of elasticity, immediately after the exposure period. The specimens were all seal ed so that no moisture loss would occur. The effect which extreme temperatures have on compressive strength as an average between groups A and B (groups mentioned above) is depicted in Figure 3 7. This plot illustrates how the 14 days of moist curing of G roup B created higher strengths than Group A when exposed to elevated heat for less time, but the difference becomes less significant as you approach longer heat exposure periods. The overall difference in elasticity between Group A and B with respect to curing time is depicted in Figure 3 8. Here it can be seen that at about 40 days of heat exposure the two concrete groups were about equal in elasticity on average. Any exposure to heat for less than 40

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53 days shows that on average there was a higher elasti c modulus (less elastic strain for a given load) for Group B. After 40 days, the contrary occurred as A had acquired a higher elastic modulus (becoming more brittle), because it had been exposed to heat at an early stage in its curing cycle. In comparing the 4 and 14 day lines, with the 90 and 180 day lines, Figure 3 9 indicate s a critical temperature, where the magnitudes of compressive strength switch hands in both Group A and B. The reason for this is in part due to the exothermic nature of the concrete curing process. To a certain extent, the concrete matures quicker when exposed to higher temperatures (see earlier discussion of Arrhenius relationship). However, when 250 F is exceeded, it can be seen that the strengths for higher exposure periods drop dramatically. This occurs because altered hydration reactions proliferate when the concrete exceeds temperatures of 250 F. Similar, but more consistent trends can be illus trated in Figure 3 9 for Group B. The lines here are much smoother due to less chaotic behaviors occurring at earlier maturities of heat exposure. Like Group A, about the same critical temperature forces the lines to switch hands (in comparison of 4 and 14 day lines with the 90 and 180 day lines) indicating an environment which becomes too hot to produce a higher strength product. Looking at the elastic modulus versus curing temperature, Figure 3 10 indicates similar trends noticeable between the relative magnitudes of the 14 and 28 day lines versus the 91 and 180 day lines when approaching a critical temperature of around 200 250 F. Although this relative behavior stays consistent, the graphs depict that there is a notably more pronounced all around decre ase in the elastic modulus magnitude as the samples are subjected to higher temperature with a given age The values of E m are indicated in some cases to decrease 50% or more when exceeding temperatures of 350 F. Another unique trend when compared to stre ngth

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54 is that the elastic modulus increases with exposure time, given a temperature of 160 F. An elastic modulus obtained at 70 F nearly equals that of the samples exposed to 160 F for 180 days. Between the characteristics of strength and elasticity, Nasse experiment points to nearly identical properties arising in concrete when exposed to temperatures of up to 160 F, when compared to 70 F, throughout the time of exposure from 0 to 180 days. The assumption that such a temperature produc es similar properties is of course only valid when considering a specimen of uniform temperature while also being sealed against moisture loss, as the experiment provided. Summary of immediate effects. (1971) experiment was that as temperatures exceeded 180 F, highly crystallized dicalcium silicate hydrate of weaker strength began to form. Mindess et al. (2003) also mentions this occurrence. The critical temperature was essentially interpolated between 160 F and 250 F, where the mechanical properties were affected the most. To get a closer look at the behavior, it might have been advantageous to have tested the concrete at temperatures within the interpolated region from 160 F to 250 F. When conditions approached 320 F, more extreme affects may have been due to hydrothermal reactions resulting in the transformation of the original tobermorite gel into new equilibrium phases, of more crystalline and lime rich calcium silicate hydrates that have poorer cementing properties (Nasser and Lohtia 2003). Delayed e ttringite formation is another product ettringite only forming after a substantial period of cooling (Mindess et al. 2003).

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55 The precuring time proved a few interesting points as wel l. First of all, the early strength of Group A was increased due to heat acting as an accelerator to the exothermic reactions. Second, it seemed that this strength quickly diminished with increased time of exposure. Furthermore, as noticeable in the temper ature ranges from 250 F to 350 F, the results indicate that the longer the curing time before exposure, the less deterioration occurred at extended ages Therefore, the hydration reactions of Group A were accelerated initially, but its strength was most rapidly lost past 4 day s. Group B may have been matured at a much slower initial rate but the strength loss was not as much as A at extended ages. 3.5.2 Long Term Effects Ettringite is a product of Portland cement hydration, which may be considered innocuous if it forms when con crete is in its plastic phase (Mindess et al. 2003, Ramlochan et al. 2003, Ramlochan et al 2004). It is produced when gypsum and tricalcium aluminate (components of C 3 A + 3CSH 2 6 AS 3 H 32 (3 13) Tricalcium Gypsum Water Ettringite Aluminate Once all of the sulfate ions from gypsum are consumed, the t ricalcium aluminate proceeds to react with the formed ettringite and water, in order to produce monosulfoaluminate: 2C 3 A + C 6 AS 3 H 32 4 ASH 12 (3 14) Tricalcium Ettringite Water Monosulfoaluminate Aluminate It has been found that delayed ettringite formation (DEF) occurs when concrete is first exposed to temperatures above 160 F during curin g, and then exposed to a well humidified environment (Ramlochan et al. 2003, Ramlochan et al. 2004, Lee et al. 2005, Sahu and Thaulow 2004). The theory behind this is that at higher curing temperatures, a significant amount of

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56 ettringite which normally for ms during the hydration process of Portland cement, as seen in Equation 3 14, is absorbed in the C S H or present in the pore solution (Sahu and Thaulow 2004). Ramlochan (2003) found that there was a considerable amount of ettringite crystallization for OP C concrete at times between 100 and 360 days after exposure to temperatures above 160 F at the time of curing. This has been found to cause extensive damage, due to the delayed growth of ettringite crystals having the ability to force cracks in the concre te by means of wedging within hydrated cement paste (Ramlochan et al 2004). The formation of ettringite is especially enhanced with the availability of sulfate, derived from either internal or external sources. One internal source is said to be pyrite (FeS 2 ) that releases sulfate ions through its oxidation process (Lee et al. 2005). Exterior sources for sulfate may include sulfur rich soils or deicer salts. Lee, et al. (2005) concluded that from petrographic and scanning electron microscopy, combined with E DAX area element mapping, that DEF had an important role in the cracking of several Iowa highway concretes. Sahu and Thaulow (2004) found that DEF forms as a result of curing temperatures being below 160F. Their study dealt with DEF in Swedish railroad t ies, which were heat cured before placement, and in service for seven years before visible map cracking was noticed. They concluded that although the ties were steam cured at 140F, other factors such as high cement content, high specific surface and high amounts of sulfate, magnesium oxide, and reactive ferrite also contributed. They also warned that DEF may very easily form in the well looking ties, if moisture is absorbed. Petrographic examination, scanning electron microscopy, and energy dispersive spec troscopy were all used in order to ascertain the nature of the cracking. 3.6 Measuring Mechanical Properties of Mass Concrete Nakamura et al. (1999) mentions that the mechanical properties that are necessary in order to predict the cracking of concrete inv olve the tensile strength and elastic modulus. However, it

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5 7 has also been found important that creep be calculated as well. An additional parameter that might be needed for future reference is autogenous shrinkage, although findings show it to be negligible when compared to the magnitude of thermal expansion. In other words, a compilation of these parameters (thermal properties discussed later) with respect to maturity time are needed if one was to input them into an FEM. Burg and Ost (1994) and Burg and Fi orato (1999) aimed at obtaining the thermal and mechanical properties of regions within large massive concrete elements at different ages (not maturities). Note that neither of these studies looked into the effects which thermal gradient played on the stre ngth, but only looked at the intrinsic properties developed as a function of real time. These studies also concentrated more on compressive strength, rather than the tensile strength of mass concrete. In their first study, Burg and Ost (1994) cast 4 ft. cu bed blocks in order to monitor the temperature development. They then took cores from the blocks, in order to obtain the critical properties, including compressive strength, modulus of elasticity, tensile strength, modulus of rupture, thermal expansion, re lative humidity, specific heat, thermal conductivity, and durability properties. There was a lot of data collected in their study, but little conclusions were drawn from graphs may easily be interpreted as reference material by outside researchers. Burg and Fiorato (1999) studied the use of high strength concrete in massive foundation elements. Their main concern was with regards to the heat generation and moisture lost du ring hydration in HSC (see discussion on autogenous shrinkage, above), and how this would affect the mechanical properties. The first step was to evaluate the temperature development within

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58 taking cores at different radii from the center, and different depths from the top. He concluded that the in place strength (derived from cores) was about 80% of the strength of the moist cured cylinders. The elastic moduli were found to be 90% to 100% of the moist cured cylinders. These conclusions seem to be consistent with findings from Nasser and Lohtia (1971), where the strength and elastic moduli were not significantly effected by the temperature exposures which were i indicated that temperatures reached about 175F in the hottest regions. This temperature actually where the It is important to note that mass concrete cracks in tension and not in compression. Therefore, it is important that an accurate tensile strength test be de veloped in order to predict this occurrence. The following section discusses the research of tensile strength tests. 3.6.1 Tensile Strength In the past, many approaches have been made in finding the tensile strength for concrete, and researchers agree that obtaining this property may pose problems with respect to both accuracy and consistency. Some methods are much more complex than others, especially those associated with direct tension. Also, some test methods may be more compatible with concrete at early ages. 3.6.1.1 Direct tensile t ests Direct tensile tests consist of applying a load which is theoretically perpendicular to crack propagation. Although it has very little margin for error, many claim this to be the best way to go about obtaining tensile strength, considering that it is done correctly. In this test, eccentricities and other extraneous stresses need to be accounted for, so that the sample breaks in a predictable

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59 region and on a failure plane relatively perpendicular to the axis of force. Th ere are several ways to go about doing this, including the following: Gripping and notches. Elvery and Heroun (1968) presented an innovative method, where a two stage casting sequence took place. This included casting the specimens in a cylindrical shape and subsequently casting an additional tapering ring of grout around the specimen ends, in tensile strengths at ages ranging from 1 28 days, with average 28 day stre ngths of about 270 psi. The methodology was sound, and the data which was found seemed precise, but the lack of data compilation made the study less convincing. Figure 3 11 displays a diagram of the specimen design that they used. Brooks and Neville (1977) described using samples similar to Elvery and Haroun (1968), with bobbin shaped ends. However, in their study they developed general power equation relationships between the direct tensile strength and splitting tensile strength, modulus of rupture, and c ompressive strength. The development of equations which relate these parameters have become somewhat controversial, and especially with regards to the relationship between tensile strength and compressive strength. They also found that the tensile strength of saturated specimens increases at a slower rate than their compressive strength, with respect to age. Al Kubaisy and Young (1975) tested for tensile strength with the use of notches, cast in a radial manner around each specimen. This was done in a simil ar two step process as indicated by Elvery and Haroun (1968). While the samples were being tested, by the direct longitudinal application of force to the notches, ultrasonic pulse velocities were conducted through the sample. In addition to this, strain di stributions, and strain magnitudes were tracked as well. It was found that 92% of the specimens broke within the region of uniform stress (the central part

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60 of the specimen, between the notches) under a loading rate of 130 psi/minute. The average tensile st rength for this loading rate was 363 psi, with a coefficient of variation of 5.8%. The diagram for this specimen may be seen in Figure 3 12. Embedded b ars. Several attempts have been made for this approach, with some experiments having more precise results than others. It consists of having bars (usually steel) cast within the test specimen, in order to apply an axial tensile force until failure occurs. Nianxiang and Wenyan (1989) approached their experiment with the knowledge of possible slippage occurring at the concrete bar interface of larger specimens. They accounted for this by making the central region of their large specimens less thick, so that the stresses would concentrate here and hopefully create failure in this region. In Figure 3 13, it can be seen that they tested both relatively large (bottom of figure) and small (top of figure) specimens. The results showed tensile strengths of 175 290 psi with a coefficient of variation of 5 15% for large specimens of different mixing proportions. For the s maller specimens, tensile strengths were much higher at 275 450 psi and had a coefficient of variation of 7 14%. They were loaded at a rate of about 30 psi/min. Ultimately, it was concluded that when comparing the large specimens to the small ones, the tes t results seemed to agree with the following empirical formula, which relates specimen size with tensile strength, (3 15) where K s is the factor of the specimen size effect and F is the cross sectional area of the specimen in cm 2 Notice that when F = 100 cm 2 K s = 1. Unlike Nianxiang and Wenyan (1989), Swaddiwudhipong et al. (2003) presented their innovative method of accounting for slippage by using embedded bars that had claw l ike grips on the ends. Their results seemed very comprehensive due to the previous studies done by Wee

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61 et al. (2000), where the claw grip method was also introduced. They found that by using a two piece mould ( Figure 3 14 ), they were able to assemble it ea sily and accurately, greatly minimizing the eccentricity caused by the asymmetric axial loading encountered in many direct tension applications. As a result, 100 out of 117 test specimens failed in the middle section, and the standard of deviation of 12 18 for tensile strain capacity was significantly lower than those of other tensile tests such as the flexure test. Gluing. Gluing has been a popular approach to direct tension testing, and is the method used in the CRD C 166 92 standard. It consists of us ing the top and bottom faces of the specimen for applying an epoxy bond to another surface (usually a steel platen) in order to apply a longitudinal tensile force. Quian and Li (2001) analyzed the effects of metakaolin on the tensile and compressive streng th of concrete, using the gluing method for the tension specimens. Zhen hai and Xiu qin (1987) also used this method, but had their aims on a depiction of a complete stress deformation curve for concrete. Reinhardt et al. (1986) was another publication, fo cusing more on fracture theory and analysis, with respect to both static and cyclic loading. One of the problems associated with gluing the specimen is that if one wishes to obtain early age tensile strength (e.g. as is critical in mass concrete), it is d ifficult to provide a bond with a wet interface of concrete. The concrete needs to be moist at early ages because it is still in a critical maturing state, where desiccation would lead to an alteration in the apparent tensile strength. There have been no p apers cited, where early age tensile strength was tested by the gluing approach. 3.6.1.2 Indirect tensile t ests Indirect tensile tests were developed with an understanding of the basic fracture mechanics of concrete. These tests are based on calculating the resultant tensile stresses caused by forces

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62 being applied on a parallel axis to the crack propagation. The indirect tension test (IDT) is the method which is most preferred when compared to splitting tension, due to it tending towards better accuracy a nd precision. However, the IDT may pose problems with respect to obtaining the properties at early ages, due to sample preparation, including the cutting of specimens and gluing of mounts for extensometers. Indirect tension test (IDT). The IDT (Figure 3 15 ) is a test where a wafer like sample having a diameter of either 4 or 6 in. is cut from a cylindrical specimen at a thickness of 1.5 in. Extensometers are subsequently mounted onto a circular face of the specimen, in order to obtain strain on a two dimens ional plane. Originally developed for asphalt, it has recently been adapted to accommodate concrete as well. Figure 3 15 is a depiction of an asphalt specimen, where the only difference between the loading scheme of it and concrete would be the associated loading and calculation software. The loading platens on the top and bottom exert a force onto the wafer, which subsequently propagates a failure crack parallel to the axis of loading, and therefore indirectly. Splitting tension t est. The splitting tensio n test, ASTM C496, involves the same concept as the IDT, but it does not measure strain and may also be less consistent at depicting the tensile strength. It consists of using a 4 x 8 in. cylinder where a load is applied transversely, in a similar manner a s the IDT. The tensile strain capacity may not be obtained from this test, but the tensile strength is calculated by the following, (3 16 ) w here T is the splitting tensile strength, P is the maximum applied load, and l and d are the length and diameter, respectively.

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63 3.6.1.3 Hydro static force i nduced tension tests This type of test takes advantage of hydrostatic forces (Figure 3 16), in order to induce an axial tensile force onto the specimen. It may either involve the use of liquids or air, to give the desired effect. This is accomplished by placing the concrete cylinder into an open ended steel jacket, where a fluid pressure is applied to th e bare curved surface. It is generally accepted that the indicated gas pressure at failure is the tensile strength of the concrete. One of the problems related to this test is that there is little known about the induced stress that develops because of the porous nature of the concrete. All that is known is that there are longitudinal stresses that develop within, as a result of hydro static stresses. Mindess et al. ( 2005 ) carried out an experiment where he tested the difference between the tensile strength of solid 4 x 8 in. cylinders vs. hollow 4 x 8 in. cylinders, placed into a steel jacket. A diagram of the testing device is indicated in Figure 3 16.. The data indicates clearly that there is negligible difference in the tensile strength between hollow cy linders and solid cylinders, in the testing of two mix designs. Depending on the mix design, the tensile strength for both solid and hollow cylinders was in the range of 4 MPa to 5.5 MPa (580 psi to 800 psi), with a standard of deviation of 0.275 to 0.375. The results agreed with the theory that the gas pressure at failure is directly indicative of the tensile strength. Clayton (1978) carried out experiments with the use of both nitrogen gas and liquid water as the loading medium. His set up was nearly ide ntical to the one above. With the use of nitrogen gas, he found that the indicated tensile strengths were much lower than that of water. However, he mainly concentrated on the importance of the loading rate and how it affected the strengths regardless of t he loading medium. The results show that the quicker loading rates led to higher tensile strength values.

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64 3.6.1.4 Flexural t est The flexural strength is one measure of the tensile strength of concrete. Often referred to as the modulus of rupture (MOR), the flexural strength may be measured by applying two point loads to an unreinforced beam at 1/3 and 2/3 of the length. The dimensions of the beam should be 6 x 6 in., with a length of at least three times the depth. The MOR is usually calculated using ASTM C 78 (third point loading). ASTM C 293 notes the procedure of center point loading, but is less conservative and may yield misleading strength values. 3.6.2 Tensile Strain and Elasticity By having the ability to accurately measure tensile strain as a functi on of stress, this also implies that an accurate estimation of the elastic modulus may be obtained from this data. strain curve is not exactly linear in the first portion, a linear assumption may be made, in order to clas sify the first phase of this curve as being elastic. Swaddiwudhipong et al. (2003) utilized claw like gripping and estimated the elastic modulus in tension from the slope of the stress strain curves (Figure 3 17). They also found that in the linearly elas tic regime (0 90% failure load) all values of the regression coefficient were greater than 0.98. In this experiment, two electrical resistance strain gages were glued onto two opposite side faces in the middle of the specimen. The tensile strain capacity of concrete refers to the strain which induces a cracking failure. The critical locations for cracking induced by thermal movement in mass concrete may occur near the surface at early ages, especially where it is exposed to rapid drops in ambient temperat ure and an accompaniment of drying shrinkage (Houghton 1976). Early work done by Houghton (1976) depicts how the tensile strain capacity was obtained from beam tests (Table 3 3) Notice that capacities for slow loading cases (creep) were included also. In this situation, a coefficient for creep was to be factored into the calculations. The

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65 modulus of rupture was used in this case to depict the tensile strength. The concrete was assumed to be linear elastic until failure; hence the theory that the tensile s train capacity is equal to the modulus of rupture divided by the elasticity. Another assumption that was made is that the elasticity for the concrete under the bending test for modulus of rupture is equal to the modulus of elasticity under a compressive lo ad. The predicted strain capacities in this table represent concretes mixed with Type II cement, moderate proportions of fly ash, air entrainment admixture, and quartzite aggregate. 3.6.3 Creep De Schutter (2002) proposed that compressive creep is valid w hen estimating thermal restraint cracking. After finding the basic creep of concrete, De Schutter decided to predict the mechanical behavior of hardening concrete by compiling the stiffnesses into a Kelvin chain model, as shown in Figure 3 18. In this mode l, E c0 cl (r) is the viscosity, and E c1 (r) is the spring stiffness. The degree of reaction, r, is simply the heat produced thus far in the reaction, divided by the total expected heat of l iberation. De Schutter (1999) calculated compressive creep at early ages by using standard creep frames, and found that loading the specimens to a value of 20% of the compressive strength at the age of loading was ideal. In his experiments, he tested concr etes of varying initial ages. He began by loading the specimens to 20% and subsequently measuring initial creep strain ( 0 ), as well as periodical creep strain. When the value for creep became relatively constant the final creep strain was be measured ( cf ), and the following calculation was made, (3 17 ) where cf is the final creep coefficient.

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66 Faria (2006) also accounted for creep when using his FEM. Because of the large stress fluctuations that occur in concrete during the early ages, the Double Power Law (DPL) was implemented, due to it being reputa ble and one of the most widely used functions for describing early age creep. This was used alongside a basic creep equation where a Taylor series expansion was used to approximate the total creep in hardening concrete. 3.7 Measuring Thermal Properties Al though the main problem with predicting cracking seems to be the evolution of found to evolve. As was mentioned by Nakamura et al (1999), the thermal propert ies needed for the prediction of thermal cracking in mass concrete include the coefficient of thermal expansion, specific heat, thermal diffusivity, and the heat of cement hydration. Laplante and Boulay (1994) reveal that there is an evolution of the CTE o f up to about 16 hours of age. De Schutter and Taerwe ( Mag. Concr. Res., 1995) found that the specific heat decreased linearly with respect to the degree of hydration. The values for thermal diffusivity and heat production were also both found to vary to a significant extent, with respect to the maturity or degree of hydration. 3.7.1 Coefficient of Thermal Expansion It has been disputed whether or not the coefficient of thermal expansion (CTE) evolves with maturity to a considerable extent. De Schutter (20 02) made an analysis for the prediction of concrete cracking, assuming a constant value of CTE. However, Laplante and Boulay (1994) had experimentally found that the concrete CTE decreased rapidly with increasing stiffness at early age, and became relative ly constant at about 16 hours. Beginning the tests at 8 hours, they Both maturity and the degree of hydration are used t o express the amount of hydration which has taken place in concrete. While the maturity has units in time (see Arrhenius, Eq. 6 ), the degree of hydration is expressed as a decimal value, equal to the amount of heat liberated thus far divided by the total h eat of liberation expected.

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67 continued until 24 hours was reached, where they had found the CTE to be at an unmoving value. CRD C 39 81 describes a test which may be used to find the linear thermal expansion of concre te. This involves obtaining the length changes of the concrete as a function of temperature change. It is very important that the accurate simulation of moisture is modeled for this experiment, due to the CTE depending highly on the moisture content of the concrete. This may be done by the immersion of the sample into water for at least a couple hours before the test. The more aged the concrete is, the more the sample may need to be immersed, due to the need for re saturation of the pores. CRD C 39 81 indic ates a procedure for finding the CTE. 3.7.2 Specific Heat The specific heat capacity of the paste may be experimentally calculated by the method used from De Schutter and Taerwe ( Mag. Concr. Res., 1995). This can be done by first supplying a known energy quantity, E 1 and measuring the corresponding temperature increase, 1 without the addition of a cement paste sample to the heptane (see Figure 3 19 ). For a second measurement, the cement paste sample is included and another energy supply, E 2 is supplie d and the temperature increase, 2 is recorded. With the use of Equation 3 19, the specific heat, c p may be calculated, (3 18 ) where m p is the mass of the paste s ample, E 2 and E 1 are the energy supplies with and without the paste sample respectively, and 2 and 1 are the temperature rises with and without the paste samples, respectively. Linear regression yielded the following equation, describing the specific he at (c p ) as a function of the degree of hydration (r) in cement paste.

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68 (J/kg K) (3 19) Figure 3 19 shows a schematic view of the calorimeter which was used to calculate the sp ecific heat of the paste. Notice that it only has minor modifications when compared to that of the calorimeter used for obtaining the thermal diffusivity. 3.7.3 Thermal Diffusivity In the work by De Schutter and Taerwe ( Mag. Concr. Res., 1995), the thermal diffusivity was also calculated for young age concrete. Embedding a thermocouple within each specimen, they measured the temperature at the center axis of the specimen vs. the time. The specimen, at temperature 0 20C), was subjected to a water bath at temperature 0 + which was 20C + 10C. The temperature (t) at the cylinder axis was then measured as a function of time. When the following equation, (3 20) is plotted as a function of time, the curve becomes linear after some time, and the slope of this curve is directly related to the thermal diffusivity. Linear regression of the results yielded the following equation, where the degree of hydration was related to the thermal diffusivity. (m 2 /h) (3 21) Figure 3 20 depicts the calorimeter used for this test. Once again, it is very similar to the others, with the only exception being that there is a thermocouple that is embedded within the cyli nder. 3.7.4 Heat Production and Heat Production Rate The heat generation Q was measured by Ballim (2003) with the use of a calorimeter. A typical schematic of the calorimeter he used is presented in Figure 3 21. The amount of heat evolved from the sample w as calculated from the following equation,

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69 ( 3 22) where m is the mass of fresh cement mixture, Cp is the specific heat capacity, and T is the change in temperature. With respect to the heat rate, the following equation was used, but only under the unique conditions of the adiabatic test noted above. ( 3 23) 3. 8 Summary Mass concrete may crack due to the thermal and relative humidity gradients that develop, or may be weakened in strength by extreme temperatures or lack of moisture. The mechanical properties that need to be quantified, in order to develop a finit e element analysis include the tensile strength, tensile strain, and modulus of elasticity. The thermal properties that need to be modeled include the coefficient of thermal expansion, specific heat, thermal diffusivity, and heat production. Although the external environmental temperatures may come into play, the main concern lies in the early age heats of hydration within mass concrete. Ballim (2003) created a two dimensional finite difference model that effectively predicted the heats of hydration to wit hin two degrees celsius. In his theory he was able to get close to the actual temperatures by accounting for maturity in the heat rate equation that he used. The maturity is an important factor, because as a function of this, the heat production changes. H e used the Arrhenius equation to calculate the maturity of his test specimens. In order to lessen these temperatures from the hydration reaction, several methods may be used. This includes the use of mineral admixtures or by precooling the aggregates and w ater.

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70 Another method to lessen the heat generation includes reducing the minimum dimension of the pour so that heat may be liberated more readily. Cracking occurs in mass concrete when the tensile strain capacity is exceeded. The causes of this may include either internal or external restraint. While internal restraint is brought about by strain gradients within the material, exterior restraint is brought about by externally applied loads. While both may be the result of thermal expansion and/or moisture c ontent, internal restraints are brought about by the gradients in strain within the mass, and external restraints are brought about by the average strain throughout the whole structure. In other words, the internal restraints may be looked at as the struct ure fighting within itself, as external restraints are brought about when an outside obstruction constricts the movement of the structure. Another consequence that needs to be obviated for within mass concrete are the absolute temperatures that develop. Th e immediate effects of extreme temperature includes the formation of highly crystallized dicalcium silicate hydrate of weaker strength that may proliferate within the concrete. This is said to especially come about when temperatures exceed 180 F (Mindess, et al., 2003, Nasser and Lohtia, 1971). One of the long term consequences of extreme te mperatures is delayed ettringite formation, and especially becomes a problem when temperatures exceed 160 F and moisture is present in the environment. In order to obtain the tensile strength of concrete, several methods may be employed. The main concern f or these tests is the method that is used in order to apply the load, without producing stress concentrations, or eccentric forces. The tensile tests include the use of embedded bars, glued loading platens, pressure tension, indirect application of load, a nd beam testing. All of these methods were studied so that one of them could be chosen for its application

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71 to early age concrete, in order to calculate the strain capacity, strength, and elastic modulus of concrete beams of different age. It is disputed wh ether all of the thermal properties of concrete evolve with age. While Laplante and Boulay (1994) claim that the coefficient of thermal expansion decreases up to 16 hours of age, others have assumed it to be constant in calculating thermal movement (De Sch utter, 2002). The specific heat and thermal diffusivity test used by De Schutter and Taerwe (1995) was aimed at finding the evolution of these properties with respect to the degree of hydration. They found that both the specific heat and thermal diffusivit y decreases with respect to the degree of hydration. Table 3 1. Contribution of cement compounds to overall cement hydration (Mindess et al. 2003). Compounds Common Name Reaction Rate Amount of Heat Liberated Strength Heat L iberation C 3 S Tricalcium Silicate Moderate Moderate High High C 2 S Dicalcium Silicate Slow Low Low initially, high later Low C 3 A + CSH 2 Tricalcium Aluminate and Gypsum Fast Very High Low Very High C 4 AF + CSH 2 Ferrite Paste and Gypsum Moderate Moderate Low Moderate

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72 Table 3 2. Properties of typical course a ggregates (Bamsforth 1984). Table 3 3. Estimation of tensile strain capacity ( Houghton 1976).

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73 Figure 3 1. Vertical t emperat ure gradients vs. time wi thin a dam lif t (Mead 1963). Figure 3 2. Vertical temperature gradients vs. time, between several l ifts (Mead 1963).

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74 Figure 3 3. Effect of minimum dimension and replacement % of fly ash on temperature rise (Bamsforth 1984). Figure 3 4. Effect of minimum dimension and replacement % of BFS on temperature rise (Bamsforth 1984).

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75 Figure 3 5. Thermal constraint device (Kim et al. 2002). Figure 3 6. Effect of internal relative humidity on capillary t ension (Grasley 2003).

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76 Figure 3 7. Compressive strength vs. time of heat exposure (Nasser and Lohtia 1971). Figure 3 8 Elastic strain vs. time of heat exposure(Nasser and Lohtia 1971).

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77 Figure 3 9 Graphs depicting compressive strength for concrete subject to high temperature (Nasser and Lohtia 197 1). Figure 3 10 Graphs depicting the elastic modulus for concrete subject to high temperature (Nasser and Lohtia 1971).

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78 Figure 3 11. Elvery and Haroun (1968) concrete tension specimen (dimensions in inches). Figure 3 12. Concrete specimen with notches ( Al Kubaisy and Young 1975).

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79 Figure 3 13 Nianxiang and Wenyan (1989) large and small specimens. Figure 3 14. Swaddiwudhipong et al. (2003) used a simple two piece mould with claw like embedments.

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80 Figure 3 15 The IDT test, with a sample of asphalt concrete. Figure 3 16 Sectional view of the nitrogen gas test, with a diagram of principle stresses (Mindess et al. 2003). Figure 3 17 Typical stress strain curves for concrete in tension (Swaddiwudhipong et al. 2003).

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81 Figure 3 18 Kelvin chain model (De Schutter 2002). Figure 3 19. Schematic drawing of a calorimeter used to measure specific heat (De Schutter and Taerwe 1995).

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82 Fi gure 3 20. Schematic drawing of a calorimeter used to measure thermal diffusivity. Figure 3 21. Schematic drawing of a calorimeter used to measure the heat of cement hydration (Ballim 2003).

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83 CHAPTER 4 FLEXURAL TEST FOR EA RLY AGE CONCRETE 4.1 Backgr ound 4.1.1 Early Age Concrete One of the challenges with this project was to determine a way in which the stress and strain behavior could be measured in early age concrete pertained to samples which were from one day to seven days old. Beam tests were determined to work fine, so as long as the strain gages were well bonded to the concrete. As early age concrete was of concern, the adhesive had to be compatible with a wet concrete surface. The preferable properties charac terized by Loctite 454 surface gel were fitting for this purpose, due to it readily reacting with moisture, in order to form a bonding interface. 4.1.2 Third Point Loading Scheme To obtain the tensile strength and strain of this concrete, it was decided th at beam tests would be used. Commonly known as third point loading, ASTM C78 describes a method which utilizes a support on each end of the beam, and point loads located at 1/3 and 2/3 of the span. The ction as well as a length of at least three times the depth. It is indicated in ASTM C78 that a load rate of 30 lbs/sec is fast enough to not induce significant creep, and slow enough so that premature rupture does not occur. This loading rate is applied u ntil the beam fails, and subsequently the stresses in the extreme fibers may be modulus of rupture (MOR). Figure 4 1 shows the stress and strain distribution, accord ing to Another method of measuring the MOR is described in ASTM C293 as the center point loading test. Unlike the third point loading scheme, this tends to create sporadic results due to

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84 the moment peaking at the center point, as oppo sed to it being constant throughout the middle third of the beam. By using the third point test, the researcher was able to confidently place the strain gage in the middle of the constant stress region so that the stress strain data could be procured. The compressive elastic modulus of the beam was then compared to compression cylinder tests where extensometers were used to measure the deformation. These cylinders were also broken, in order to compare the empirical relationship between crushing strength and elastic modulus with that of the compression region of the beam. 4.1.3 Compression Test for Elastic Modulus The standard test procedures of ASTM C39 and C469 were generally followed in running the compressive strength and elastic modulus test. Figure 4 3 shows the set up for this test, where 4 in x 8 in cylindrical specimens were used. Th e two ends of the specimen were ground evenly before testing to insure even loading during the test. Two 4 inch extensometer displacement gages, which were held by f our springs, were mounted on the sides of the specimen. The specimen was then placed in a compression testing machine. The testing machine used was hydraulic controlled and had a maximum capacity of 220 kip s Load was applied to the specimen at a consta nt loading rate of 26 kip/minute until failure The outputs from the displacement gages and the load cell from the testing machine were connected to a data acquisition system, which records the data during the test The average displacement reading was us ed to calculate the strain, and the reading from the load cell was used to calculate the stress. 4.2 Flexural Test Materials 4.2.1 Instrumentation Strain Gages Tokyo Sokki Kenkyujo Co., Ltd., Type PL 60 11 3LT Loading Frame Instron 3384, with third poi nt loading attachments Signal Conditioning Unit National Instruments SCXI 1000

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85 Two Computers One for strain, and the other for load cell acquisition 4.2.2 Sample Accessories Concrete Ingredients Per ASTM specification (see Res ults and Discussion) Drum or Shear Concrete Mixing Device Vibration Table Mineral Oil Plastic Cover for Beams 4.2.3 Preparation Accessories Glue Loctite 454 surface gel Non Bonding Polymer Sheath Packaged with strain gages Rubber Setting Cloth Clean and damp Acetone Standard concentration Sand Paper Fine Grit Masking Tape 4.3 Flexural Test Procedure 4.3.1 Casting 1. Wipe the forms with mineral oil, so as to produce a non stick surface 2. Mix batch of concrete per ASTM C192 3. Procure slump, unit weight, and any plastic properties of concern 4. Place concrete into the beam molds so that of the volume is filled 5. Vibrate the half filled molds for 12 seconds on a vibration table 6. Fill the molds to the top wit h concrete and vibrate for 12 seconds 7. Trowel the top surface of the concrete, using a wet instrument 8. Cover the filled molds with a plastic cover, so that negligible moisture evaporates from the surface.

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86 4.3.2 Sample Preparation and Storage 1. De mold after 24 hours and either begin to prepare the samples for one day testing, or store the samples in a lime bath solution for later age testing. 2. Procure specimen of desired age and let it sit on the counter top for 30 minutes for moderate evaporation. 3. Sand the cent surface area. Note that the top and bottom faces should be the original side faces of the molded specimen. This allows for smooth surfaces to be used, as opposed to the trowelled sur face. 4. Wipe away the concrete dust with a dampened cloth. Then, proceed to wipe the sanded region with an acetone dampened cloth. Do this for both faces. 5. Draw a line along the width at each of the 1/3 portions as well as the mid point of the specimen. Draw another line along the length in the center of the specimen. Do this for both faces. 6. After acetone has apparently evaporated, place a pencil lead thick line of glue onto the strain gage, and carefully center it onto one of the marked faces of the specimen 7. Carefully place the polymer sheath onto the top of the gage and work a finger over it lightly to encourage bonding. 8. press firmly for approximately 5 minutes. 9. Repeat 14 16 for the other face. 10. Gently secure the wires in the area where they connect to the gage by taping them down in this region. This will prevent the fine gauged wires from tearing. Do this for both gages. 4.3.3 Testing 1. Carefully center the beam onto the loading frame, so that the 1/3 marks accurately align with the loading platens. Note: Ensure that the strain gage wires will not be crimped by the loading action of the test frame! 2. Connect both gages to the SCXI 1000 unit, ensuring proper quarter bridge c onfiguration 3. Run the loading apparatus at a rate of 30 lbs/sec, acquiring both voltage data (from strain gages) and the load cell data. 4.3.4 Data Analysis 1. Determine Vr, from the voltage output data with the following equation,

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87 (4 1) where Vx is the variable voltage; Vi is the initial voltage, and Ve is the excitation voltage. 2. Determine the strain from the following equation, (4 2) where GF is the gage factor. 3. Determine the stress, from the load output data with the following two equations, (4 3) (4 4) Where P is the load cell readings; L is the span length (not the beam length); c is the depth; and I is the moment of inertia of the section. 4. Correlate the output values so that they match to one another. Do this by observing when the strain voltages begin to increase. Lastly, check the failure st ress and strain to ensure that they are terminating at approximately the same value. 5. The mechanical properties shall be calculated in the following manner: Tensile Strength the peak tensile stress before the beam breaks. Tensile Strain Capacity the pea k tensile strain before the beam breaks. Elastic Modulus of Tenison See Equation 4 5. (4 5) Where ft and t is the stress and strain at the given percent of strength and capacity, respectively. Elastic Modulus of Compression See Equation 4 6. (4 6) 6. A good way to compare the elastic modulus of compression with another experimental extensometers, as was done in our research project.

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88 4.4 Resul ts and Discussion Concrete used contained fine aggregate with a fineness modulus of 2.5 and coarse Type I/II Portland cement. In addition to these ingredients, water redu cing admixture was added (WRA 64) to make the concrete more workable. Overall, the mix seemed to be quite wet, and as a result it had a higher slump of 10 inches. Tables 4 1 and 4 2 give a summary of the materials used. The main objectives of this mix incl uded quantitatively and qualitatively observing the strain gage results and assessing the feasibility in attaching them to the early age concrete. Another goal was to observe the evolution of the early age tensile strain capacity, elastic modulus, and tens ile strength for one and three day specimens It was observed that by following the procedure outlined above, there was no apparent problems in attaching the gages, nor was there any qualitative problems observed during the loading period. The numerical da ta yielded a steady and relatively linear progression of strain as the beams were loaded at 30 lbs/sec (Figure 4 5 and 4 6). Although there was no noticeable discontinuity in the stress versus strain relationship for either compression or tension, the resu lts seemed to imply that the compressive elastic modulus was more reliable than the tensile elastic modulus. Figure 4 4 graphically depicts the comparison of different methods used to calculate the elastic modulus in compression. For the three day samples, the elastic modulus for the compression region in the beam (3771 ksi) almost identically matched the empirical predictions for the elastic modulus (3745 ksi). The empirical relationship was obtained by breaking cylinders (by compression) in order to get t heir strength, and using it in the equation obtained in ACI 8.5.1 2002 (Equation 4 7).

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89 (4 7) Another value for the elastic modulus in com pression was obtained for the 3 day samples average (3928 ksi) compared fairly well with the empirical average (Table 4 3). The MOR and elastic modulus both displayed consistent results with age (Table 4 4). As expected, the concrete became stiffer and stronger with age. Regarding the tensile strength, the average MOR at one day (0.457 ksi) displayed an expectable evolution towards the three day MOR (0.494 ksi). The el astic modulus displayed more change than strength did when comparing 1 day (2868 ksi) with 3 day (3377 ksi) beams. This is due to there being less tensile strain with respect to stress. One of the issues with the results was that the elastic modulus in te nsion did not match that of the compression elastic modulus. The Bernoulli Theorem assumes that the neutral axis is located in the center of the beam, and that there is a linear distribution of stress and strain. The flexural test that is used in our study for early age concrete is therefore partly discredited due to the compressive and tensile elastic moduli not matching to one another. This is due to the tension region undergoing micro cracking and plastic deformation before the ultimate failure occurs. When comparing these results to literature findings, it seems that the change in these properties with respect to age displays proportionate trends in behavior, but only display magnitude consistency within the testing method and not as much between other methods employed. For example, the direct tension test used by Swaddiwudhipong et al. (2003) produced strength values that were less than those obtained by the MOR tests in this research. It is believed that the direct tension test produces less strength d ue to the eccentricities that can result from a slight miss alignment of the applied load. Due to the constant region of stress produced in the

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90 third point beam tests (Figure 4 2), it is believed that there is a greater tendency to produce results that are more representative of the true properties. The tensile strain capacities for the beam tests were very consistent with respect to one another (Table 4 5), therefore producing a very low standard of deviation. This was due to the concrete consistently rup turing at a similar tensile strain at a given age. The one day concrete had an average tensile strain capacity of 183 while the three day samples had and average of 159 This holds consistent with the fact that the stiffness (E tension) increased consi derably, between one and three days. 4.5 Summary and Conclusions The results of the beam tests using surface mounted strain gages show that it is feasible to run this test on early age concrete. Consistent stress strain plots can be obtained from this te st. The measured tensile strength and elastic modulus (tension and compression) increased and the tensile strain capacity decreased with age from one day to three days. Although the use of Loctite 454 surface adhesive created an adequate bond at the concre te gage interface, it is evident that the tension region of the beam behaved differently than the compression region. The compressive elastic modulus obtained from the beam test compared well to the estimated elastic modulus from compressive strength usin g the ACI equation (Equation 4 7), and the measured elastic modulus from compression cylinders. However, the tensile elastic moduli were generally lower than the elastic moduli in compression. This is thought to be due to micro cracking within the tension region at an early stage in the loading process. Due to this occurring, the stress versus strain curve appears to be flatter, and therefore produces a lower modulus. The observed difference between the measured strains in the tensile zone versus the compre ssive zone warrants further investigation into this area.

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91 Table 4 1. Material weights used. W/C Ratio F. Aggregate (lb) (lb) Cement (lb) Water (lb) WRA 64 (ml) 0.45 123.45 204.96 88.80 45.59 100.00 Table 4 2. Mix proportions used, according to PCA recommendations. W/C Ratio F. Aggregate (lb/cuy) Cement (lb/cuy) Water (lb/cuy) 0.45 1040 1800 755 340 Table 4 3. Mechanical properties for three day aged cylinders. Sample # Age (Day) E comp Extensomet er (ksi) E comp ,Empirical (ksi) 1 3 3727.9 3886.7 2 3 4098.7 3819.5 3 3 3958.5 3529.7 AVERAGE 3 3928.4 3745.3 Table 4 4. Mechanical properties for the beam. Sample # Age (Day) MOR (ksi) E comp Beam (ksi) E ten Beam (ksi) t Capacity ( ) 1 1 0.474 2901.9 2901.3 184 2 1 0.438 3420.2 2778.3 184 3 1 0.457 3550.9 2923.8 181 AVERAGE 1 0.457 3291.0 2867.8 183 4 3 0.489 3371.3 3611.5 159 5 3 0.552 4106.1 3323.4 159 6 3 0.440 3835.5 3195.7 159 AVERAGE 3 0.494 3770.9 3376.9 159

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92 Table 4 5. Standard deviation for various tests and ages. Sample Type 1 Day Beam 3 Day Beam 3 Day Cylinder MOR (ksi) 0 .018 0.056 NA E comp (ksi) 343.257 371.603 187.226 E comp Empirical (ksi) NA NA 189.704 E ten (ksi) 78.286 212.987 NA t Capacity ( ) 1.732 0.000 NA Figure 4 1. Theoretical stress and strain distribution through cross section

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93 Figure 4 2. Loading scheme and moment diagram. Figure 4 3. Loading scheme for the measurement of elastic mod ulus in compression, with the use of extensometers.

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94 Figure 4 4. Comparison of methods used to obtain compression elastic modulus for concrete. This plot depicts three day samples.

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95 Figure 4 5. Typical plot of 1 day stress

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96 Figure 4 6. Typical plot of 3 day stress

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97 CHAPTER 5 SPECIFIC HEAT FOR EA RLY AGE CONCRETE AND ITS COMPONENTS 5.1 Background The specific heat of concrete (c) is an essential property, because it can be directly used to calculate the temperature increase of a material with known mass, when given the amount of thermal energy supplied. The following equation depicts how the specific heat may be calculated experimentally, ( 5 1) where E is the applied thermal energy (kJ), m is the mass of the material (kg), and T is the change in temperature of the material (C). The specific heat is also related to the thermal conductivity in the following way, (5 2) where is the thermal conductivity of the material, a is the thermal diffu sivity, and is the density. With respect to mass concrete, the thermal energy that is of main concern is that of the hydration reaction of the cementitious materials. When the specific heat is used as a modeling parameter alongside other properties incl uding thermal diffusivity, coefficient of thermal expansion, and heat generation, one is able to model the temperature rise and expansion of a concrete mass. Customarily, a differential scanning calorimeter (DSC) is used to obtain the specific heat of mate rials (ASTM E 1269 05). However, the problem with applying this test to concrete is that because the required sample amount is very small (a few milligrams), it would not be representative of the concrete as a whole. Also, it was desired that a more simple procedure

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98 could be developed (than that compared with the DSC procedures) and where less expensive equipment would be needed. The goal of this research was to therefore use larger samples that would be tested by precise, yet more simple procedures. The sp ecific heat tests used in this research involved the use of a calorimeter fabricated by the researcher, in accordance with De Schutter and Taerwe, 1995, and another calorimeter designed and fabricated by the researcher. The first experiment (De Schutter an d Taerwe, 1995) involves the use of two baths, with an interior one of oil and an exterior one of polypropylene glycol. The liquids used in these baths were chosen due to their ability to rapidly transfer heat. In the interior bath, a stir paddle, heater, and two thermocouples were placed within. The exterior bath was of the circulatory type, and regulated a constant temperature at approximately that of the room (Figure 5 1). The procedure involves supplying a known flux of heat energy into the interior bat h and analyzing the resulting rise in temperature within The stir paddle was used to distribute the heat evenly throughout the interior bath. In the first step, a known quantity of heat is provided to the interior bath without the concrete sample ( E1), and the resultant temperature rise ( 1) of the oil bath is measured. Following this, the concrete is added to the oil bath and another quantity of energy is supplied ( E2) and the change in temperature of the concrete ( 2) is measured. In this case, the change in concrete temperature may be measured without the embedment of a thermocouple by extrapolating from the temperature vs. time plot for the interior bath (Figure 5 2). In order to measure the heat energy of both cases, a watt meter was used that was able to plot watts as a function of time. With this plot, the energy could be obtained by taking the area under the curve.

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99 The region of the graph (Figure 5 2) where the temperature peaks (above the value 2) represents the process of the concrete establishing thermal equilibrium with the oil. After this peak has resided and linearity is achieved, the linear portion of the graph can be extrapolated to obtain 2. Once this is calculated, Equation 5 3 may b e used to determine the specific heat of and a linear transient st ate that was noticed after the heater was shut off. (5 3) The calorimeter that was designed by the researcher was based on a different concept than s experiment. The scheme was to have a fully insulated flask, in order to contain all of the heat energy input. In this case, there was a negligible transient state after the heater was shut off. This experiment also utilized two thermocouples, that were u sed to indicate any thermal gradient that was present within the calorimeter, as shown in Figure 5 3. The researcher chose to do this in order to stress the importance of establishing thermal equilibrium. Although the concept was different, the procedures between the two approaches were very similar. For the insulated test, there was also a run with and without material. The specific heat was also calculated in a similar manner, except for the T2 term being measured directly (from thermal equilibrium), as opposed to extrapolation. 5.2 Insulated Flask Test 5.2.1 Calorimeter Accessories Dewar flask 4000ml capacity Heat transfer oil Duratherm 600, heat transfer fluid Heater Gaumer, 500 Watt, with screw plug Air motor With a drill chuck attachment

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100 Sti r paddle Powered by air motor and fitting into chuck fitting Wooden Mount Used to cover the top of the flask and to mount accessories Material Specimen 100 250 grams of material, per Table 5 1. 5.2.2 Data Instrumentation Data Acquisition Daq PRO 5300 Watt Meter Watts Up Pro, Power Analyzer Thermistor Needed to verify temperatures Thermocouple Three type J Scale Accurate to 0.1 gram 5.2.3 Cast Procedure 1. Cast 4 in by 8 in cylindrical specimens with caps to seal moisture 2. De mold the cylin ders at 24hrs +/ 1hr 3. Place the cylinders into a lime bath solution to provide a neutral curing environment for the concrete. Withdraw them at necessary ages for testing 5.2.4 Test Procedure Calibration 1. Ensure that the Daq Lab is configured properly. T his includes the following menus: ensure that input filter is on, that no average is taken, and that temperature is in C. 2. Ensure that the three inputs used are set to read as type J thermocouples. Also be sure that the rate is set to every second for 5,000 samples. 3. Warm up the data acquisition system for the thermocouples by turning it on and having it read temperatures. 4. Ensure that the accessories are put into position on the wooden mount. Orient the thermocou ples so that one touches the bottom surface of the flask, and the other is in the center. Keep all of the accessories in the same positions for each run. Also, place one of the three thermocouples outside of the beaker to read the air temperature. 5. Zero the dewar flask (without the mount), and leave it on the scale. 6. Check to ensure that the heat transfer oil is equal to the room temperature. This may require leaving the oil in the room for 24 hours before testing. 7. Add oil to the flask, so that a two inch lip is left between the level of the oil and the top edge. Record the mass of the oil.

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101 8. Place the flask into position underneath the air motor apparatus and put the wooden cover on the flask with the paddle, heater, and thermocouples placed into position. Fit the stir paddle into the chuck fitting on the air motor, and ensure that it vertically passes through the center of the stir paddle hole on the mount. 9. Start the stir paddle. Adjust the regulator so that there is a 6 psi driving pressure. 10. Ensure that there is close to zero thermal gradient within the flask. This is done by observing the deep and middle thermocouple temperatures as the stir paddle turns. Also, check that the temperature in the room is approximately equal to the temperatures within the flask. 11. Turn off the data acquisition system after a final check of the internal flask gradients, and any differential between the room and flask. 12. Begin experimentation by simultaneously initiating the readings for the thermocouples, starting the heater (obtaining power measurements) and starting a timer. It needs to be made certain that both systems are synchronized, so that the power measurement coincides with the temperature measurement. This may take some trial running by the researcher to check the time when t he Daq Lab initiates its inputs. It does not occur the 13. Leave heater running for four minutes. 14. Unplug the heater from the watt meter at exactly four minutes, leaving the Daq Lab to continue making measure ments.. After this, unplug the watt meter from the power outlet. For the Watts Up PRO, the data will be saved to system, even though the meter was abruptly unplugged from the wall. Note: The Watts Up PRO will begin to generate two second intervals between readings if the meter is left plugged in for more than 17 minutes. Therefore, the meter should be unplugged immediately after heating so that one second intervals will be obtained to coincide with temperature readings. 15. Continue to obtain temperature re adings for thermocouples for a duration of time in accordance with Table 5 1. The duration of the calibration run depends on the duration of the type of material tested in the materials test. Even though the calibration run does not include material, it ne eds to be run for the same time period as the material run. 16. After this time period has elapsed, press the escape button on the acquisition system to end the logging. 17. Stop the stirrer remove it from the chuck and remove the wooden mount (with all componen ts) from the flask. Set it, along with its mounted components onto a paper towel. Wipe off any oil on the heater, stir paddle, and thermocouples. 18. calibrated fluid.

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102 19. Place the fluid into a refrigerator for about an hour to bring the temperature back down to Note: It is recommended that a few batches of oil are prepared, so that the resear cher may use one that is room temperature, while another is cooling back down 20. Thoroughly clean the flask of oil residue. 21. Upload the data for thermocouples and power into excel. The watt meter unfortunately does not have the capacity to store more than one data file. 5.2.5 Test Procedure With Material 1. Repeat steps 1 5 above. 2. If using concrete or paste, read step 3 below, else skip to step 4. 3. and gently hammering the w afer in order to cleave the sample into sizes similar to peanut brittle. Place the pieces into a tupperware container with the lid closed until needed for test. 4. Add material to the flask in accordance with Table 5 1. If using paste or concrete, pat the sam ple dry with an absorbent cloth before adding. This is to rid the sample of any free moisture at its surface. Record the mass of the sample. 5. Add the batch of oil that was calibrated previously into the flask. The height of oil will be slightly higher than in the calibration run, due to it being displaced by the addition of the material. Note: The mass may be slightly less than the calibration run after pouring the oil into the flask. Add a small amount of fresh oil if necessary. 6. Place the flask into positio n underneath the air motor apparatus, without the mount. Pull the deeper thermocouple out of the mount 3 4 in from its original position, so that it will not lodge onto the material. Put the wooden cover on the flask with the paddle, heater, and thermoco uples (one of them raised). Swiftly stab the raised thermocouple into the material so that it resumes the same position it had during calibration, but fully embedded into the sample. Fit the stir paddle into the chuck fitting on the air motor, and ensure t hat it vertically passes through the center of the stir paddle hole on the mount. All of the mounted accessories need to be in an identical position as the calibration run. 7. Start the stir paddle. Adjust the regulator so that there is a 6 psi driving pressu re. 8. Ensure that there is close to zero thermal gradient within the flask. This is done by observing the deep and middle thermocouple temperatures as the stir paddle turns. It may take a few minutes of monitoring this, now that there is one thermocouple in the material and one outside of it. Also, check that the temperature in the room is approximately equal to the temperatures within the flask.

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103 9. Turn off the data acquisition system after a final check of the internal flask gradients, and any differential bet ween the room and flask. 10. Begin experimentation by simultaneously initiating the readings for the thermocouples, starting the heater (obtaining power measurements) and starting a timer. It needs to be made certain that both systems are synchronized, so that the power measurement coincides with the temperature measurement. This may take some trial running by the researcher to check the time when the Daq Lab initiates its inputs. It does not occur the 11. Leave heater running for four minutes. 12. Unplug the heater from the watt meter at exactly four minutes, leaving the Daq Lab to continue making measurements. After this, unplug the watt meter from the power outlet. For the Watts Up PRO, the data will be saved to sy stem, even though the meter was abruptly unplugged from the wall. Note: The Watts Up PRO will begin to generate two second intervals between readings if the meter is left plugged in for more than 17 minutes. Therefore, the meter should be unplugged immedia tely after heating so that one second intervals will be obtained to coincide with temperature readings. 13. Continue to obtain temperature readings for thermocouples for a duration of time in accordance with Table 5 1. 14. After this time period has elapsed, p ress the escape button on the acquisition system to end the logging. 15. Stop the stirrer remove it from the chuck and remove the wooden mount (with all components) from the flask. Set it, along with its mounted components onto a paper towel. Wipe off any oil on the heater, stir paddle, and thermocouples. 16. remove any material that is in suspension and place the cover on it. 17. Place the fluid into a refrigerator for about an hour to bring the temperature back down to 18. Thoroughly clean the flask of oil residue. 5.2.6 Analysis Note: This analysis section may be used to format either the calibration o r material data file 1. After uploading the data file from the calibration and material run, trim out all of the except for time, power (watts), and watt hours.

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104 2. Ensure t hat the entries were taken in one second intervals for both acquisition systems. The uploaded data from the watt meter is usually given in units of hours. The Daq Lab outputs 60 entries per written minute (one second per entry). 3. Trim out the initial (zero ) power readings so that the first power entry, when the heater was plugged in, matches with the first temperature reading. This synchronizes the data. 4. After synchronizing, convert all of the time entries into units of seconds. 5. Trim out the excessive readi ngs of the synchronized data so that there are a total number of data points (seconds) equal to that indicated by Table 5 1. For example, a lime rock data file would have a total of anywhere from 625 sec 700 sec of data points. 6. Write an equation in a col umn that calculates the total energy outputted from the heater. The equation that converts power to energy for each interval (one second) is indicated by the following: (5 4) W here i indicates the time step, P indicates the power (Watts), t is the time (seconds), and E is the energy (joules). Copy this equation down the column until the last thermocouple reading. One can convert to kilojoules by multiplying the first term by the reciprocal of 1000. 7. Calculate the heat capacity ( C) of the calorimeter (calibration run), and the calorimeter with material (material run) as indicated in Equation 5 2. The values for E and T (change in energy and temperature, respectively) are given by one of the three methods outlined below Equation 5 2. Use the calculated energy. (5 5) Single value m ethod. This method utilizes only one final and one initial measured value. The E term is calculated by subtracting the first energy term (should be zero) from the final energy term. For T, the initial reading of the deep and shallow thermocouple is averaged, and subtracted from the final averaged temperature between the deep and sh allow thermocouple. Average analysis (11 v alues) This method uses the last and first eleven measured increments (seconds). The E term is calculated by subtracting the average of the first eleven energy terms from the average of the final eleven energy te rms (in this case, the final eleven energy terms should be the same). For T, the first eleven readings of the deep and shallow thermocouples are averaged (total of 22), and subtracted from the final eleven averaged temperatures between the deep and shall ow thermocouple (also a total of 22 values).

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105 Average analysis (6 v alues) This method uses the last and first six measured increments (seconds). The E and T terms are calculated the same as in the eleven value analysis, except that the last and first six terms are used instead. Moving average analysis (11 v alues) This method calculates the E and T terms by taking the average of the surrounding 10 values about a point in time (five less and five greater than the point. With the use of this approach, on e can graphically depict the way that the calculated specific heat changes as a function of time. Figure 5 4 and 5 5 show examples of two temperatures that were calculated. The temperatures indicated here umn within the box and the other in the second) readings at a well established equilibrium time. It should also be noted that both the calibration run, and the material run need to be used in parallel with this method. In other words, the moving average T terms need to be calculated for both runs, in order to compute the specific heat. The moving average for E should be constant, due to the heater being off at these times. 8. Calculate the specific heat ( c ) of the material by referring to Equation 5 3. The theoretical specific heat should be calculated for each of the three analysis methods indicated above. (5 6) Where mm is the mass of the material, CTot is the heat capacity obtained from the run that included the material an d calorimeter, and CCal is the heat capacity obtained from the run that included the calorimeter by itself. 5.3 Transient Test 5.3.1 Calorimeter Accessories Interior bath Stainless steel beaker, 4000ml Interior bath oil Duratherm 600, heat transfer flu id Heater Gaumer, 500 Watt with screw plug Air Motor With a drill chuck attachment Stir paddle Powered by air motor Wooden Mount Used to cover the top of the interior bath and to mount accessories Exterior Bath Circulatory, to maintain constant t emperature of 28C Exterior Bath Fluid Dowfrost heat transfer fluid Concrete Specimen 125 grams of concrete material 5.3.2 Data Instrumentation Data Acquisition Daq PRO, 5300 Watt Meter Watts Up Pro, Power Analyzer Thermistor Purpose is to check

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106 Thermocouples Three type J Scale Accurate to 0.1 grams 5.3.3 Cast Procedure 1. Cast 4 in by 8 in cylindrical specimens with caps to seal moisture 2. De mold the cylinders at 24hrs +/ 1hr 3. Place the cylinders int o a lime bath solution to provide a neutral curing environment for the concrete. Withdraw them at necessary ages for testing 5.3.4 Test Procedure Calibration 1. Ensure that the beaker will sit in the exterior bath so that the top lip of it is above the leve l of dowfrost fluid by about two inches. Place a step on the bottom of the bath if needed, in order to hold the beaker at this level. 2. Engage the exterior circulating bath so that it is maintaining a constant temperature of approximately equal to the room t emperature. Note: Leave this temperature setting the same for the material run. 3. Ensure that the Daq Lab is configured properly. This includes the following menus: ensure that input filter is on, that no average is taken, and that t emperature is in C. Ensure that the three inputs used are set to read as a type J thermocouples. Also be sure that the rate is set to every second for 5,000 samples. 4. Warm up the data acquisition system for the thermocouples by turning it on and having it read temperatures. 5. Ensure that the accessories are put into position on the wooden mount. Orient the thermocouples so that one hovers over the bottom surface of the beaker, and the other is in the center. Keep all of the accessories in the same positions for each run. Also, place one of the three thermocouples outside of the beaker to read the air temperature. 6. Zero the beaker (without the mount), and leave it on the scale. 7. Check to ensure that the heat transfer oil is equal to the exter ior bath temperature. Since the exterior bath is set to the room temperature, it may be best to leave the oil in the room for 24 hours to allow equilibrium. 8. Add oil to the beaker, so that a two inch lip is left between the level of the oil and the top edge Record the mass of the oil.

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107 9. Place the beaker into position within the exterior bath and underneath the air motor apparatus. 10. Put the wooden cover on the beaker with the paddle, heater, and thermocouples placed into position. Fit the stir paddle into the chuck fitting on the air motor, and ensure that it vertically passes through the center of the stir paddle hole on the mount. 11. Start the stir paddle. Adjust the regulator so that there is a 6 psi driving pressure. 12. Ensure that there is close to zero thermal gradient within the beaker. This is done by observing the deep and middle thermocouple temperatures as the stir paddle turns. Also, check that the temperature in the exterior bath is equal to the temperatures within the beaker. This may take a few minutes, but not an excessive amount of time, due to the oil being at room temperature and the bath also being set to regulate itself at room temperature. 13. Turn off the data acquisition system after a final check of the internal beaker gradients, and any differenti al between the room and beaker. 14. Begin experimentation by simultaneously initiating the readings for the thermocouples, starting the heater (obtaining power measurements) and starting a timer. It needs to be made certain that both systems are synchronized, so that the power measurement coincides with the temperature measurement. This may take some trial running by the researcher to check the time when the Daq Lab initiates its inputs. It does not occur the moment that the 15. Leave heater running for three minutes. 16. Unplug the heater from the watt meter at exactly three minutes. After this, unplug the watt meter from the power outlet. For the Watts Up PRO, the data will be saved to system, even though the meter was abruptly unp lugged from the wall. Note: The Watts Up PRO will begin to generate two second intervals between readings if the meter is left plugged in for more than 17 minutes. Therefore, the meter should be unplugged immediately after heating so that one second interv als will be obtained to coincide with temperature readings. 17. Seize the data acquisition of the temperatures. The calibration run for the transient test only needs to last for three minutes. 18. Stop the stirrer remove it from the chuck and remove the woode n mount (with all components) from the beaker Set it, along with its mounted components onto a paper towel. Wipe off any oil on the heater, stir paddle, and thermocouples. 19. label the calibrated fluid. 20. Place the fluid into a refrigerator for about an hour to bring the temperature back down to Note: It is

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108 recommended that a few batches of oil are prepared, so that the researcher may use one that is room temperature, while another is cooling back down 21. Thoroughly clean the beaker of oil residue. 22. Upload the data for thermocouples and power into excel. The watt meter unfortunately does not have the cap acity to store more than one data file. 5.3.5 Analysis Calibration 1. After all data from the calibration run has been uploaded to excel, trim out all of the except for time, power (watts), and watt hours. 2. Ensure that the entries were taken in one second intervals for both acquisition systems. The uploaded data from the watt meter is usually given in units of hours. The Daq Lab outputs 60 entries per written minute (one second per entry). 3. Trim out the initial (zero) power readings so that the first power entry, when the heater was plugged in, matches with the first temperature reading. This synchronizes the data. 4. After synchronizing, convert all of the time entries into units of seconds. 5. Trim out the excessive readings of the synchronized data so that there are a total number of data points (seconds) equal to the total heating time plus two seconds. For example, a concrete data file would have a total of 182 seconds for t he calibration run. 6. Write an equation in a column that calculates the total energy outputted from the heater. The equation that converts power to energy for each interval (one second) is indicated by the following: (5 1) Where i indicates the time step, P indicates the power (Watts), t is the time (seconds), and E is the energy (joules). Copy this equation down the column until the last thermocouple reading. One can convert to k ilojoules by multiplying the first term by the reciprocal of 1000. 7. Calculate the heat capacity ( C) of the calorimeter (calibration run), as indicated in Equation 5 2. Use the calculated energy. (5 2) E is obtained by taking the energy at 182 seconds (should be the same as that at 181 seconds, but slightly more than 180, the shut off time) and subtracting the energy at zero seconds from it (should be zero). For T, the last three temperature readings f or

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109 thermocouples one and two are averaged (total of six values, from 180 182 seconds) and the initial thermocouple readings (at time zero) are averaged and subtracted from the final. 5.3.6 Test Procedure With Material 1. Repeat steps 1 6 in Test Proced ure Calibration. 2. hammering the wafer in order to cleave the sample into sizes similar to peanut brittle. Place the pieces into a tupperware container with the lid c losed until needed for test. 3. Add material to the beaker in accordance with Table 5 1. Make sure to pat the concrete sample dry with an absorbent cloth before adding. This is to rid the sample of any free moisture at its surface. Record the mass of the samp le. 4. Add the batch of oil that was calibrated previously into the beaker. The height of oil will be slightly higher than in the calibration run, due to it being displaced by the addition of the material. Note: The mass may be slightly less than the calibrat ion run after pouring the oil into the beaker. Add a small amount of fresh oil if necessary. 5. Place the beaker into position underneath the air motor apparatus, without the mount. Put the wooden cover on the beaker with the paddle, heater, and thermocouples Fit the stir paddle into the chuck fitting on the air motor, and ensure that it vertically passes through the center of the stir paddle hole on the mount. All of the mounted accessories need to be in an identical position as the calibration run. 6. Start th e stir paddle. Adjust the regulator so that there is a 6 psi driving pressure. 7. Ensure that there is close to zero thermal gradient within the beaker. This is done by observing the deep and middle thermocouple temperatures as the stir paddle turns. Also, ch eck that the temperature in the exterior bath is equal to the temperatures within the beaker. It may take a few minutes of monitoring this, especially now that there is material in the beaker 8. Turn off the data acquisition system after a final check of the internal beaker gradients, and any differential between the room and beaker. 9. Begin experimentation by simultaneously initiating the readings for the thermocouples, starting the heater (obtaining power measurements) and starting a timer. It needs to be mad e certain that both systems are synchronized, so that the power measurement coincides with the temperature measurement. This may take some trial running by the researcher to check the time when the Daq Lab initiates its inputs. It does not occur the moment that the 10. Leave heater running for three minutes (same as calibration run). 11. Unplug the heater from the watt meter at exactly three minutes, leaving the Daq Lab to continue making measurements. After this, unplug the wat t meter from the power outlet.

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110 For the Watts Up PRO, the data will be saved to system, even though the meter was abruptly unplugged from the wall. Note: The Watts Up PRO will begin to generate two second intervals between readings if the meter is left plug ged in for more than 17 minutes. Therefore, the meter should be unplugged immediately after heating so that one second intervals will be obtained to coincide with temperature readings. 12. Continue to obtain temperature readings for thermocouples for a dur ation of time in accordance with Table 5 1. 13. After this time period has elapsed, press the escape button on the acquisition system to end the logging. 14. Stop the stirrer remove it from the chuck and remove the wooden mount (with all components) from the beak er Set it, along with its mounted components onto a paper towel. Wipe off any oil on the heater, stir paddle, and thermocouples. 15. remove any material that is in susp ension and place the cover on it. 16. Place the fluid into a refrigerator for about an hour to bring the temperature back down to 17. Thoroughly clean the beaker of oil residue. 5.3.7 Analysis With Material 1. After all data from the material run has been uploaded to excel, trim out all of the excessive time, power (watts), and watt hours. 2. Ensure th at the entries were taken in one second intervals for both acquisition systems. The uploaded data from the watt meter is usually given in units of hours. The Daq Lab outputs 60 entries per written minute (one second per entry). 3. Trim out the initial (zero) power readings so that the first power entry, when the heater was plugged in, matches with the first temperature reading. This synchronizes the data. 4. After synchronizing, convert all of the time entries into units of seconds. 5. Trim out the excessive readin gs of the synchronized data so that there are a total number of data p oints (seconds) equal to the equilibrium time indicated in Table 5 1 For example, a concrete dat a file would have a total of anywhere from 575 to 625 seconds for the material run. 6. Wri te an equation in a column that calculates the total energy outputted from the heater. The equation that converts power to energy for each interval (one second) is indicated by the following:

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111 (5 1) Where i indicates the time step, P indicates the power (Watts), t is the time (seconds), and E is the energy (joules). Copy this equation down the column until the last thermocouple reading. One can convert to kilojoules by multiplyin g the first term by the reciprocal of 1000. 7. Calculate the heat capacity ( C) of the calorimeter (calibration run), as indicated in Equation 5 2. Use the calculated energy. (5 2) E is obtained by taking the energy at the final reading and subtracting the energy at zero seconds from it (should be zero). For T, a graph depicting the temperature vs. the time needs to be constructed. The final value is equal to the intersection of th e trend line for the heat up period (from zero to 181 seconds) and the extrapolated trend line for the linear transient period (the last 200 seconds of data). Figure 5 7 shows a graphical depiction of this technique. Excel makes this possible by including an equation with the trend line. By solving for these two equations for two unknowns, one may obtain the time and temperature that they intersect. The initial thermocouple readings (at time zero) are averaged and subtracted from the final extrapolated valu e, in order to get T. 8. Calculate the specific heat ( c ) of the material by referring to Equation 5 3. The theoretical specific heat should be calculated for each of the three analysis methods indicated above. (5 6) Where m m is the mass of the material, C Tot is the heat capacity obtained from the run that included the material and calorimeter, and C Cal is the heat capacity obtained from the run that included the calorimeter by itself. 5.4 Results and Discussion 5.4.1 Calorim eter Development and Sensitivity As the calorimeter apparatus and testing procedures were being developed, several issues were discovered. The air stirrer that was used for the flask test was not an immediate solution to effectively diffusing heat througho ut the flask. The first attempt was to use an electronic motor as the driving mechanism for the stirring device. The problem with this apparatus was that it

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112 produced an excessive and inconsistent amount of heat (from the motor resistivity) that was conduct ed down the stirrer shaft, and into the calorimeter. As a consequence, the temperature curves for this method displayed inconsistency that would lead to erroneous calorimetric measurements. With this discovery, a stirring device that was powered by an air motor would be developed and used in this test. By setting a bearing into the wooden mount (the cover of the flask) to guide the rotations of the shaft, this would also serve to minimize the heat produced by the stir paddle. For the insulated flask procedu re, the calibration runs (without material) display a near constant temperature after the heating is terminated (very slight thermal dissipation from insulative imperfections), showing that the air stirrer was an effective device to use for this applicatio n. As a result, this device was chosen as the chief diffuser of fluid for this test. Another developmental issue with the flask test was establishing equilibrium between the calorimeter and the material that was being tested. In order to calculate the spec ific heat of these materials, it was essential that this state was established, in order to assume a homogenous temperature. It was discovered that depending on the material tested for, various equilibrium times were required. The key to this development w as to balance characteristics between equilibrium time and the amount of mass that was used. Although a small amount of mass would allow for a shorter equilibrium time, other considerations needed to be made. The problem with using too small of an amount o f mass that would be tested within 3800 grams of fluid was that it made the test sensitive to temperature error. As can be seen in Equation 5 6, the term 1/m m acts as a multiplier of the differences between the E/ T terms, within the parenthesis. With this being said, the 1/m m term may amplify any error encountered with the thermocouples when a small amount of mass is used. On the other hand, a large amount of mass leads to time duration issues (for equilibrium) where other experimental error may come into play. Although the flask

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113 is fully insulated, and negligible heat loss or input is assumed for relatively short time periods, longer experimental durations (i.e., 1200 seconds) may lead to slight alterations in the calorimetric conditions that result in more sporadic results. With respect to the insulated flask test, the data analysis procedure for the different materials evolved with trial and error. As indicated in the insulated flask analysis section above, there were four different approaches that were used to analyze the data. The single value method had the most flaws, due to it taking the average of two thermocouple readings at one particular point in time. This was found to not be accurate enough, due to the noise involved with thermocouple readings. This noise had the potential to throw off the value obtained for specific heat by a considerable amount. For example, Table 5 7 depicts how the standard deviation for the single value method is greater than t he other methods. The average methods (6 and 11 values) were then used, in order to help soften the noise of the thermocouples. The procedures for these are also included in the insulated flask analysis section above. The values proved to have less variat ion, due to the readings being averaged in order to cancel the plus or minus variability in the thermocouple readings. However, due to only one interval of values being used for the average, the method could be improved upon by taking multiple intervals of average values and subsequently averaging them. The final approach to getting a representative value for specific heat, involved taking the average of the final five moving average values (see analysis procedure section and Figures 5 4 through 5 6). This method was determined to be the most accurate way of obtaining specific heat, due to it involving the averages of several increments throughout the time period where the material was in equilibrium with its surroundings. Although this method was the most d esired, it

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114 also displayed variability due to thermocouple noise. A plot showing the average specific heat as a function of time is displayed in Figure 5 8. 5.4.2 Transient Test Complications One of the issues that was encountered in using the transient tes t procedure was that the linear state of temperature decrease was very difficult to locate. In doing several analyses, a slight change in the interval for which the linear transient state was depicted would change the value for T to an extent where the value for specific heat would vary excessively. When looking at Figure 5 7, one may note that because there is adequate heat conduction between the two bath systems, the curve would continue to decay asymptotically until the tempe rature of the interior bath would return to that of the exterior bath (that at time zero) This creates an infinite amount of perspectives as to where the linear decay window of this curve should be located. In fact, if one was to use a window of time whe re the two baths were nearly equal, than a value of zero would be found for T. in the literature, the lack of procedural information made it hard to replicate in the lab. Another setback for replication was that the fluid heptane (used by De S chutter, in his analysis) was too toxic to use in this experiment. In place of Heptane, a nonreactive heat transfer fluid was used. The results reported in Table 5 2 display the variability that was encountered in the transient test approach. As a result o f this variability, no viable conclusions could be drawn from this data. 5.4.3 Mix Materials and Parameters The specific heat tests were carried out in order to analyze Florida limestone, sand, cement paste, and concrete. While the insulated test was used to analyze all four materials, the transient test was only attempted for the concrete samples. The data collected for the inert materials (no

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115 hydration) consists of five rock and five sand sample tests. The data collected for the reactive materials include d two samples tested for each age of 1 day, 3 days, and 7 days curing time. It was ensured that both the paste and concrete had the same water to cement ratio (w/c = 0.38). For the paste mix, Florida Portland Cement, Type I/II was used. The weights used fo r the paste mix were 5 lbs of cement and 1.9 lbs of water. After mixing the paste by hand with gloves, specimens were prepared in 2 in x 4 in cylinder moulds. The specimens were vibrated, covered with plastic wrap, and left overnight to cure. They were dem olded the following day, and set into a lime water bath at the same temperature. When used for testing, they were reduced into smaller pieces and the surface of the material was patted dry (see procedures above). Table 5 3 indicates the proportions of mate rials used for the concrete mixture. The plastic properties that were obtained included a slump of 5 in and an air content of 7%. The use of superplasticizer and water reducing admixtures were needed in order to make the concrete workable at a water to cem ent ratio of 0.38. After mixing these materials in a small drum mixer, the specimens were prepared in 4 in x 8 in cylinder moulds. They were then sealed against moisture loss and left overnight to cure. After 24 hours, they were demolded and placed in the same lime bath as the paste samples until needed for testing. 5.4.4 Concrete Specimens The results of the concrete tests for the insulated flask procedure are indicated in Tables 5 4 through 5 5. While all the materials that were tested in the insulated fl ask displayed some variability with respect to specific heat, the values formed a noticeable trend from which conclusions could be drawn. The flask test for concrete yielded results that were relatively consistent, when compared to the other materials. Fig ure 5 9 shows a material run, where the temperature gradient is reduced with time, until equilibrium is finally reached at about 625 seconds. Note that the curve which is

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116 below the other one represents the thermocouple buried by the material. For the 1 day 3 day and 7 day tests, the specific heats obtained from the moving average method were 1.45, 1.50, and 1.74 kj/kg*k, respectively. Figure 5 10 portrays how there was a noticeable increase in the specific heat of concrete, particularly between 3 and 7 day s of age. This increase is thought to be due to the excessive ingress of water into the concrete as a result of the reaction kinetics. With more water located within the specimen than was initially present, the specific heat would inevitably increase due long as this water were not to react to form different components. Although the water that reacts with cement paste is used to make calcium silicate hydrate and calcium hydroxide, it is believed that the reaction kinetics acted to drive excessive moisture (more than stoichiometrically balanced) into the specimen. It has been found (Ulm and Coussy, 1996) that a s the cement and water hydration reactions proceed, the water diffus es through the material from the regio n s of the hydrated cement towards regions of unhydrated cement where products form on an instantaneous manner, relative to the timescale of the diffusion process (Figure 5 11). He also mentions that with respect to reaction kinetics, the diffusion of water is said to be the most dominating mechanism of the hydration reaction. In consideration of this, it would therefore not be expected that a linear increase in the specific heat of concrete would occur with respect to age, but rather an exponential curvatur e of increase. This is due to the reaction rate of the concrete being non linear as well, brought about by the acceleration of the hydration taking place due to the addition of not only more reactive resource (water), but more heat (from the reaction itsel f) that acts as an accelerator in an exothermic reaction. Therefore, the diffusion of the water may be thought of as accelerating.

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117 These reaction kinetics especially hold true in concretes (or pastes) where the water to cement ratio is lower than the idea l stoichiometric ratio. It has been found that the ideal range for a water to cement ratio should be between 0.42 and 0.45, in order to get a complete reaction between these components (Mindess et. al., 2003). The diffusion potential was therefore substant ial in this concrete mix, considering that the w/c ratio was mixed at 0.38. 5.4.5 Paste Specimens The time that the cement paste took to reach equilibrium was similar to that of concrete, as Figure 5 12 displays. The cement paste specimens also displayed a nalogous behavior to that of the concrete specimens with regards to specific heat. The specific heat increased a considerable extent between 3 and 7 days (Figure 5 13). As the 1 day (1.50 kj/kg*k) and two day (1.52 kj/kg*k) averages were nearly equivalent, the 7 day average (2.2 kj/kg*k) showed marginal increase. The greater increase in specific heat (when compared to concrete) is thought to be due to the greater concentration of cem ent paste, therefore causing a greater amount of moisture diffusion to take place from the hydrated, towards the unhydrated regions within. The greater increase in specific heat during the latter interval (3 to 7 days) may have been brought about by the accelerated reaction kinetics (as occurred in the concrete specimens). Simila r to concrete, it is believed that the affinity for water, from the unreacted cement paste within, created a saturation of the reacted media spaces (in the exterior region) with moisture. As this moisture is only an addition to the previously reacted media it serves as free water, and therefore raises the specific heat. 5.4.6 Rock Samples specific heat of lime rock had the least amount of variation (Figure 5 14). Table 5 8 summarizes all of the runs that were carried out for this material, and Figure 5 15 graphically displays the

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118 low variability and approximate average. Because these samples were dried in the oven d concrete samples), the microstructure of the test samples was very consistent. Another advantageous property of this material was that the needed equilibrium time was not very long, considering there was 250 grams of material that was used. It was also off from what was obtained experimentally. The moving average results show that the specific heat of the rock was 0.91 kj/kg*k, with a standard of deviation of 0.149 that was ob tained from five test runs. It was essential to keep the rock (and other materials) in a dry place, where they would acquire room temperature. 5.4.7 Sand Samples Sand was the most difficult material to test, due to a long duration of time being needed for thermal equilibrium to be established. Initially, 250 grams of material was used, where it was observed that the diffusivity of heat into the sand took much longer than it was expected. The amount of sand had to be reduced, in order to run the test in a sh orter time interval that would not create the error that would be incurred from longer intervals. It took 1200 seconds for only 100 grams of sample to reach equilibrium (Figure 5 16). Even though the sand was kept completely dry, and at room temperature, t he combination of these two factors (low mass and long duration) was the cause of inconsistent results, as can be seen in Table 5 9. The average specific heat for sand was 1.33 kj/kg*k, with a standard deviation of 0.91. 5.5 Summary and Conclusions The tra nsient experimental set up was tried but found to be unsuccessful. This was due to the inability to find a linear transient window of time that would be used to extrapolate for T It

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119 given to this research for it being a catalyst to develop the insulated flask test. Although there are some improvements that may be made for the insulate d flask test, the procedures were successful in producing viable results for concrete, cement paste, and lime rock when using the 11 value moving average analysis. With the onset of further hydration, and an affinity for moisture, both the concrete and cem ent paste displayed an increase in measured specific heat with respect to curing time. This increase in specific heat with time for the cement paste and concrete is believed to be due to the ingress of water into the sample. De Schutter and Taerwe (1995) found that paste samples sealed against moisture displayed a decrease in specific heat with age due to moisture consumption. However, the samples used in our study were stored in a lime bath where water was able to diffuse into the samples. Ulm and Coussy (1996) indicate that water diffuses from regions of hydrated, towards regions of unhydrated cement paste. It is believed that the measured specific heat of cement paste increased more than that of concrete, because of the higher concentration of cement wit hin the cement paste samples. This occurred even though hydrated cement paste has a much less permeable microstructure than that of concrete (Halamickova et al., 1995). The reason for placing the samples into a 100% humidity environment in this research wa s to replicate the typical requirements for many mass concrete pours, where the surfaces need to be kept wet and free from moisture loss. The results obtained for the specific heat of lime rock compared well with that of other sources, at 0.91 kj/kg*k. This material fared well for the insulated flask test, due to the feasibility in producing consistently dry, thermally stable, and thermally diffusible samples. Its higher thermal diffusivity allowed the lime rock to undergo short flask tests with a relat ively large

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120 amount of material (250 grams). These were the factors that contributed to more consistent and accurate results. High variability in test results was obtained when the specific heat test was performed on mal diffusivity, the mass had to be reduced and the duration time had to be increased. The longer duration of the test introduced higher variability because of heat loss to the environment and energy from the stirring paddle. With the use of a smaller samp le, the heat capacity of the sample is much smaller than the heat capacity of the system. As a result, little variability in the test system would translate into a much greater variability in the test results for a small sample. Table 5 1. Equilibrium tim es for the flask test and transient test. Mass (g) Total Heating Time (sec) Well Established Equilibrium Time, Including Heating (sec) Material Dewar Transient Test Dewar Transient Test Dewar Transient Test Lime Rock 250 NA 240 NA 625 70 0 NA Sand 100 NA 240 NA 1200 NA Cement Paste 125 NA 240 NA 725 750 NA Concrete 125 250 240 180 625 800 575 625

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121 Table 5 2. Specific heat and statistical results for transient test Run Specimen Age ( Day) Specific Heat (kj/kg*k) Average Specific Heat Per Day (kj/kg*k) STDEV Per Day 1 DeschConc(1),f1 1 1.600 1.011 0.832 2 DeschConc(2),f2 1 0.423 3 DeschConc(3),f1 3 2.420 2.717 0.420 4 DeschConc(4),f2 3 3.014 5 DeschConc(5),f1 7 2.118 2.005 0.161 6 DeschConc(6),f2 7 1.891 Table 5 3. Material weights used for concrete mix. W/C Ratio Fine Aggregate (lb) Coarse Aggregate (lb) Cement (lb) Water (lb) Water Reducing Admixture (ml) Superplasticizer (ml) 0.38 37.74 59.56 23.81 9.54 20 40 Table 5 4. Specific heat values for the insulated flask test for concrete. Specific Heat (kj/kg*k) Run Specimen Age (Day) Single Value 11 Values (Avg) 6 Values (Avg) Average of Last 5 Moving Averages 1 Conc(1),f1 1 1.438 1.319 1.660 1.286 2 Conc(2),f2 1 1.177 1.414 1.287 1.611 3 Conc(3),f1 3 0.555 1.142 0.961 1.167 4 Conc(4),f2 3 1.684 1.664 1.986 1.826 5 Conc(5),f1 7 2.291 1 .690 1.782 1.706 6 Conc(6),f2 7 2.144 1.837 1.950 1.778

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122 Table 5 5. Averages and standard deviation results for the insulated flask test for concrete. Specific Heat (kj/kg*k) Age (Day) STDEV, Single Value Method STDEV, 11 Value Method STDEV, 6 Value Method STDEV, Moving Average Method Single Value Method 11 Value Method 6 Value Method Moving Average Method 1 0.185 0.067 0.263 0.229 1.307 1.366 1.473 1.449 3 0.799 0.369 0.725 0.466 1.120 1.403 1.473 1.497 7 0.104 0.104 0.119 0.050 2.218 1.764 1.866 1.742 Table 5 6. Specific heat values for the insulated flask test for cement paste. Specific Heat (kj/kg*k) Run Specimen Age (Day) Single Value 11 Values (Avg) 6 Values (Avg) Average of Last 5 Moving Averages 1 Paste(1),f1 1 0.875 1.072 1.317 1.127 2 Paste(2),f2 1 1.754 1.765 1.824 1.872 3 Paste(3),f1 3 2.479 2.082 2.332 2.022 4 Paste(4),f2 3 0.975 1.011 1.071 1.013 5 P aste(5),f1 7 3.399 2.061 2.163 2.048 6 Paste(6),f2 7 3.007 2.302 2.500 2.310

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123 Table 5 7. Averages and standard deviation results for the insulated flask test for cement paste. Age (Day) STDEV, Single Value Method STDEV, 11 Value Method STDE V, 6 Value Method STDEV, Moving Average Method Specific Heat (kj/kg*k) Single Value Method 11 Value Method 6 Value Method Moving Average Method 1 0.622 0.490 0.359 0.527 1.314 1.418 1.571 1.499 3 1.064 0.758 0. 891 0.713 1.727 1.547 1.702 1.518 7 0.277 0.170 0.238 0.186 3.203 2.182 2.332 2.179 Table 5 8. Results for the insulated flask test for lime rock. Run Specimen Single Value Method (kj/kg*k) 11 Value Method (kj/kg*k) 6 Value Meth od (kj/kg*k) Moving Average Method (kj/kg*k) 1 Rock(2),f2 0.630 0.737 0.858 0.728 2 Rock(3),f3 1.092 0.940 1.079 0.929 3 Rock(4),f1 1.691 0.978 1.021 0.951 4 Rock(5),f2 1.668 1.106 1.179 1.123 5 Rock(6),f3 2 .249 0.848 1.076 0.821 AVG 1.466 0.922 1.043 0.910 STDEV 0.621 0.139 0.118 0.149

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124 Table 5 9. Results for the insulated flask test for sand. Run Specimen Single Value Method (kj/kg*k) 11 Value Method (kj/kg*k) 6 Value Method (kj/kg*k) Moving Average Method (kj/kg*k) 1 Sand(9),f3 0.410 0.878 1.366 0.779 2 Sand(10),f1 0.266 0.074 0.320 0.056 3 Sand(11),f1 1.686 1.959 2.067 2.055 4 Sand(12),f1 2.727 2.187 2.381 2.229 5 Sand(13),f2 0.383 1.591 1.700 1.546 AVG 1.095 1.308 1.567 1.333 STDEV 1.081 0.918 0.795 0.909 Figure 5 1. Set up of the transient state calorimeter.

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125 Figure 5 2. Extrapolation technique (De Schutter a nd Taerwe, 1995) to acquire the temperature change of the concrete. Figure 5 3. Set up of the insulated calorimeter.

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126 Figure 5 4. The temperatures within the box (C) represent those that are averaged for the point of 622 seconds (indicated immediately left of the box).

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127 Figure 5 5. The temperatures within the box (C) represent those that are averaged for the point of 623 seconds. This is the last possible point that may be averaged using eleven values.

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128 Figure 5 6. The specific heat is obtained by av eraging the final five values (boxed in) that were calculated using the examples in Figures 5 5 and 5 6.

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129 Figure 5 7. Typical extrapolation technique used for the transient test, in order to obtain T2. Figure 5 8. Moving average for a 7 day cement paste sample, where each point represents the specific heat obtained from the average of eleven temperatures.

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130 Figure 5 9. Typical curves depicting the establishment of thermo equili brium within the flask calorimeter, in using concrete specimens. Figure 5 10. The evolution of concrete specific heat with age, in using the moving average method.

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131 Figure 5 11. Hydration sketch of microdiffusion of free wa ter through layers of already formed hydrates to unhydrated cement. Figure 5 12. Typical curves depicting the establishment of equilibrium for the paste samples within the flask calorimeter.

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132 Figure 5 13. The evolution of cement paste specific heat wit h age, in using the moving average analysis method. Figure 5 14. Curves depicting the establishment of thermo equilibrium for lime rock within the flask calorimeter.

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133 Figure 5 15. The results obtained from 5 individual specific heat runs for lime rock Figure 5 16. Graph showing the longer duration of time required for equilibrium to occur for the sand samples.

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134 CHAPTER 6 SUMMARY, CONCLUSIONS AND RECOMMENDATION S 6.1 Summary and Conclusions 6.1.1 Flexural Test The results from the beam tests using su rface mounted strain gages show that it is feasible to run this test on early age concrete. Consistent stress strain plots can be obtained from this test. The measured tensile strength and elastic modulus in tension and compression increased and the tensi le strain capacity decreased from one day to three day ages. The compressive elastic modulus, obtained from the beam test compared well to the estimated elastic modulus from compressive strength using the ACI equation (see Equation 4 7), and the measured e lastic modulus from compression cylinders. The compressive elastic modulus was higher than the tensile elastic modulus. This is believed to be due to additional micro cracking in the tension region that produced a flatter curve for the stress versus strai n relationship. The observed difference between the measured strains in the tensile zone versus the compressive zone warrants further investigation into this area. 6.1.2 Specific Heat Test The transient experimental set up was tried but found to be unsucce ssful. This was due to the inability to find a linear transient window of time that would be used to extrapolate for T The procedures that were developed for the insulated flask test were successful in producing viable results for concrete, cement paste, and lime rock when using the 11 value moving average analysis. With the onset of further hydration and an affinity for moisture, both the concrete and cement paste displayed an increase in specific heat with respect to curing time. This is believed to be due to the ingress of water into the sample, as was studied by Ulm and Coussy (1996). It is believed that the measured specific heat of cement paste increased more than concrete because of the higher concentration of cement within the cement paste samples. Lime rock fared well for the insulated flask test, due to the feasibility in producing consistently dry and thermally diffusible samples. Its higher thermal diffusivity allowed the limerock to undergo short flask tests with a relatively large amount of ma terial (250 grams). These were the factors that contributed to more consistent and accurate results.

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135 High variability in test results was obtained when the specific heat test was performed on s had to be reduced and the duration of time had to be increased. The longer duration of the test introduced higher variability because of heat loss to the environment and energy from the stirring paddle. With the use of a smaller sample, the heat capacity of the sample is much smaller than the heat capacity of the system. As a result, little variability in the test system would translate into a much greater variability in the test results for a small sample. 6.2 Recommendations for Further Research 6.2.1 Characterization of Maturity For both of the tests that were developed, additional measurements could be made in order to classify the relative age (also known as maturity) of the concrete. With the use of thermocouples placed into the centroid of these sp ecimens, the temperature may be measured with respect to time. By acquiring the history of temperature vs. time for a concrete specimen, the maturity may be calculated and is related to the area under this curve. 6.2.2 Flexural Test It is recommended that the acquired stress and strain data should be automatically synchronized, so that the stress and strain at a particular gage point may be more reliably matched with one another. This may involve the use of a single computer (as opposed to two) in order to relate these parameters. A study should be conducted, that involves the nonlinear stress versus strain behavior of the tensile and compression regions for the flexural test in early age concrete. The issues to address include the adjustment of the neutral axis and moment of inertia (cracked versus uncracked) as the specimen is being loaded. The early age of these specimens makes them more vulnerable to alterations of these parameters as a function of load magnitude. 6.2.3 Specific Heat Test Due to the sensi tivity to error, more precise and less sporadic temperature measurements may be needed with instrumentation such as thermistors or resistance temperature detectors (RTDs). For the flask test, produce a minimum amount of heat transfer between the calorimete r and surrounding environment. This may involve more insulation or a more consistent stirring mechanism. By combining these improvements with a larger collection of test data, the averages for specific heat should further converge upon a representative val ue. Use a different amount of values to calculate a moving average. For instance, a more representative moving average specific heat might include data with less or more points than was done in our study (i.e. 7, 9, 13, or 15, as opposed to 11).

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136 Measure th e amount of water within the samples at each test day, so that the ingress of moisture may be known and accounted for in the specific heat calculations. This can be done by oven drying the specimens and observing the change in moisture with respect to age. With these results, a componential specific heat analysis can be carried out. This includes accounting for the masses of all the materials (including water) so that a componential specific heat of concrete may be compared with a measured specific heat of concrete specimens. Calibrate the test system using a material sample of known specific heat, such as copper.

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137 LIST OF REFERENCES ACI Committee 207 (2005), 207.1R Guide to mass c oncrete Farmington Hill, USA. Al Kubaisy, M.A., and Young, A.G. (1975 Failure of concrete under sustained tension Mag. Concr. Res 27 (100), 171 178. Cem Concr Compos 26(6), 695 703. Bamsforth P.B. (1984). Concrete Society Digest no 2, Concrete and Cement Association. Bentz, D.P., and Jenson, O.M. (2004). Mitigation strategies fo Cem Concr Compos 26, 677 685. Brooks, J.J., and Neville, A. M. (1977). A comparison of creep, elasticity and strength of concrete in tension and compression Mag Concr Res 29(100), 131 141. Burg, R.G., and Ost, B.W. (1994). strength concrete (including th ree year d ata) Research and Development Bulletin RD104, Portland Cement Association Skokie, Illinois, U.S.A. Burg, R.G., and Fiorato, A.E. (1999). strength concrete in massive foundation e lements Research and Development Bulletin RD117 Portland Cement Association Skokie, Illinois, U.S.A. Clayton, N. (1978). Fluid pressur Mag Concr Res 30(102), 26 30. De Schutter, G. (1999). Degree of hydration based Kelvin model for the basic creep of early age Mater Struct 32(218), 260 265. De Schutter, G. (2002). Finite element simulation of thermal cracking in massive hardening concrete elements using degree o Comput Struct 80, 2035 2042. De Schutter, G., and Taerwe, L. (1995). General hydration model for Portland cement and blast Cem Concr Res 25(3), 593 604. De Schutter, G., and Taerwe, L. (1995). Specific heat and thermal dif fusivity of hardening Mag Concr Res 47(172), 203 8. Elvery, R.H., and Haroun, W. (1968). A direct tensile test for concrete un der long or short term Mag Concr Res 20(63), 111 116. Modelling of concrete at early ages: Application t o an externally restrained C em. Con cr Compos 28, 572 585.

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138 Grasley, Z.C. (2003). oncrete A Report of an Investigation, Department of Civil Engineering, UIUC. e rmeabi lity and chloride ion diffusion in Portland cement m ortars: relationship to sand content and critical pore d iameter. Cem. Concr. Res., 25, 790 802. Houghton, D.L. (1976). Determining tensile strain capacity of mass concrete. J Am Concr Inst 7 3(12), 691 700. Kim, Jang Ho Jay, Jeon, Sang Eun, and Kim, Jin Keun (2002). Development of new device for measuring thermal stresses Cem Concr Res 32, 1645 1651. Klein, A., et al. (1963). Symposium on Mass Concrete American Concrete Institute, Detroit, Michigan, 199 218. Laplante, P., and Boulay, C. (1994). Evolution of the thermal expansion coefficient of concrete as a function of Mater Struct In Fre nch, 27(174), 596 605. Lee, H., et al. (2005). The formation and role of ettringite in Iowa highway concrete Cem. Concr. Res. 35, 332 343. Lee, K.M., et al. (2006). Autogenous shrinkage of concrete containing granulated blast furnace sla g Cem. Concr. Res. 36, 1279 1285. Malhorta, V.M., and Mehta, P.K. (1996). Pozzolanic and cementitious materials. Gordon and Breach Publishers, Amsterdam, 113. Mead, A.R. (1963). Temperature Instrument Observatio Symposi um on Mass Concrete. American Concrete Institute, Detroit, Michigan. 151 178. Mindess, S., Young, J.F., and Darwin, D. (2003). Concrete 2 nd ed., Pearson Education, Inc., Upper Saddle River, NJ., 261 264 and 296 300. Mindess, S., et al. (2005). The nitrog en gas tension test of concrete Construction Materials and Mindess Symposium, Vancouver, B.C., Aug. 22 24, 2005. Naik, T.R., Singh, S.S., and Hossain, M.M. (1994). Permeability of concrete cont aining large Cem Concr Res 24(5), 913 922. Nakamura, H., et al. (1999). Estimation of thermal crack resistance for mass concrete structures with ACI Struct J 96(4), 509 518. Nasser K.W., and Lohtia R.P (1971). Mass concrete properties a t high temperatures J Am Concr Inst 68 (3), 180 186. Nianxiang, X., and Wenyan, L. (1989). Determining tensile properties of mass concrete by ACI Mater J 86(3), 214 219.

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139 Qian, X., and Li, Z. (2001). The relationships betwe en stress and strain for high performance Cem Concr Res 31, 1607 1611. Ramlochan, T., et al. (2003). The effect of pozzolans and slag on the expansion of mortars cured at elevated temperature, Part I: Expansive behavior Ce m Concr Res 33, 807 814. Ramlochan, T., et al. (2004). The effect of pozzolans and slag on the expansion of mortars cured at elevated temperature, Part II: Microstructural and micr Cem Concr Res 34, 1341 1356. Reinhardt, H.W., Cornelissen, H.A.W., and Hordijk, D.A. (1986). Tensile tests a nd failure J Struct Eng 112(11), 2462 2477. Sahu, S., and Thaulow, N. (2004). Delayed ettringite formation in Swedish concrete railroad Cem. Concr. Res. 34(9), 1675 1681. to the Transportation Research Board for possible pre sentation and publication. Serafim, J.L., and Guerreiro, M. (1969). Autogenous and hygrometric expansion of concrete. J Amer Concr Inst 6 6(9), ACI, Detroit, Michigan, 716 719. Swaddiwudhipong, S., Lu, Hai Rong, and Wee, Tiong Huan (2003). Direct te nsion test and tensile strain cap Cem Concr Res 33(12), 2077 2084. Townsend, C.L. (1981). Control of Cracking in Mass Concrete Structures U.S. Department of the Interior Bureau of Reclamation, Washington, D.C. Ulm, F., and Coussy, O. (1995). Modeling of thermomechanical couplings of concrete at early ages J Eng Mech 121(7), 785 794. Ulm, F., and Coussy, O. (2001). What is a massive concrete structure at early ag es? Some J Eng Mech 127( 5), 512 522. Manual ETL 1110 2 542 Washington, D.C. Manual EM 1110 2 2200 Washington, D.C. Wee, T.H., Suryavanshi, A.K., and Tin, S.S. (2000). Evaluation of rapid chloride permeability test (RCPT) results for concret ACI Mater J 97(2), 221 228. Wilson, E.L. (1968). tion of temperatures within mass concrete s tructures Report of an Investigation, Report no. 68 17, Structural Engineering Laboratory, University of California, Berkely.

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141 BIOGRAPHICAL SKETCH Samuel J. Smith received a degree in civil engineering at the University of Florida in the summer of 2005. During the previous summers of acquiring this degree, he pursue d internships in the field as a surveyor, where he gained field knowledge with respect to road and bridge work. Following this, Sam interned at Gerding Engineering Corporation, where he was involved in structural design. He continued his education at the University of Florida the following fall and procured his Master of Engineering in Civil Engineering in the summer of 2007. He aspires to become a consultant in the field of structural engineering.