Lime rock in concrete, Part 1. Method for mixing and placing concrete...

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Lime rock in concrete, Part 1. Method for mixing and placing concrete...
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Lime rock in concrete, Part 1. Method for mixing and placing concrete...
Houston, Harry H.
Morgen, Ralph A.
Place of Publication:
Gainesville, Fla.
College of Engineering, University of Florida
Publication Date:


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City of Gainesville ( local )
Cements ( jstor )
Compressive strength ( jstor )
Construction aggregate ( jstor )


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Bulletin no. 7

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Source Institution:
University of Florida
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University of Florida
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All applicable rights reserved by the source institution and holding location.
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AAA4336 ( LTQF )
AFC1485 ( LTUF )
45636059 ( OCLC )
022010100 ( ALEPHBIBNUM )


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Engineering and Industrial Experiment Station

of the

University of Florida

Bulletin No. 7

June, 1944


Part 1




The Engineering and Industrial Experiment Station
The Engineering Experiment Station was first approved by
the Board of Control at its meeting on May 13, 1929. Funds
for the Florida Engineering and Industrial Experiment Station
were appropriated by the Legislature of the State of Florida in
1941. The Station is a Division of the College of Engineering
of the University of Florida under the supervision of the State
Board of Control of Florida. The functions of the Engineering
and Industrial Experiment Station are:
a) To develop the industries of Florida by organizing and
promoting research in those fields of engineering, and the re-
lated sciences, bearing on the industrial welfare of the State.
b) To survey and evaluate the natural resources of the
State that may be susceptible to sound development.
c) To contract with governmental bodies, technical societies,
associations, or industrial organizations in aiding them to solve
their technical problems. Provision is made for these organ-
izations to avail themselves of the facilities of the Engineering
and Industrial Experiment Station on a co-operative financial
basis. It is the basic philosophy of the Station that the indus-
trial progress of Florida can best be furthered by carrying on
research in those fields in which Florida, by virtue of its location,
climate, and raw materials, has natural advantages.
d) To publish and disseminate information on the results
of experimental and research projects. Two series of pamphlets
are issued: Bulletins covering the results of research and in-
vestigations by staff members; and Technical Papers, reprinting
papers or reports by staff members which have been published
For copies of Bulletins, Technical Papers or information on
how the Station can be of service, address:
The Engineering and Industrial Experiment Station
College of Engineering
University of Florida
Gainesville, Florida
JOSEPH WEIL, Director.


Engineering and Industrial Experiment Station Bulletin No. 7


Method for Mixing and Placing Concrete
Using Soft Florida Lime Rock as Aggregate




JUNE, 1944


One of the main objectives of the Engineering and Industrial
Experiment Station is to evaluate and develop the natural re-
sources of Florida.
The work reported in this Bulletin covers some of the results
of a general investigation on the bulk uses of Lime Rock in line
with that objective. The studies were made possible through
the financial assistance and co-operation of the Limerock Asso-
ciation of Florida, Inc. Many of the earlier figures used in this
Bulletin were obtained by Edward C. Barrett to whom the
authors are indebted.
The prime purpose in publishing these data, at this time,
is to make available, reliable information on the use of Lime
Rock for small construction. It is realized that, in the post-war
construction period, many small structures will be built and it
is hoped that Lime Rock will contribute its rightful share in
this building. Some of the uses to which it is believed Lime
Rock Concrete should be put are blocks for small residences,
silos, sidewalks, floors, various farm and industrial buildings
and many specialty items.
The work is continuing and a later Bulletin will give data
for larger structures, beams and reinforced concrete.
JOSEPH WEIL, Director.


F orew ord . .................................... ................ ........... ...-- 2

Introduction ................. .... .. .. .... ...................................... 5

P procedure ... ............. .. ........... .... ...... ...................... .............. 8

Method for Mixing and Placing ....... ...................... 13

Effect of Mixing Water on Compressive Strength .... .............. 17

Effect of Particle Size on Compressive Strength ...... .. .................... 23

Effect of Clay on Compressive Strength ............. ..................... 27

Favorable and Unfavorable Curing Conditions ............................. 29

Most Favorable Conditions for Lime Rock Concrete ........................... 31

A brasion Resistance ............ ......... ...... ........ ..................... .. 32

Results and Conclusions ......................3.. ........ .......... ....... 84

Appendix--Field Moisture Test ..... ............. ................ 34



Fig. 1.-Typical buildings and sidewalks made of Lime Rock concrete.

Lime Rock as aggregate for concrete has been under investi-
gation for several years. All the tests and experimental work
included in this bulletin were conducted in an effort to study
the physical properties of a concrete made by the incorporation
of soft Lime Rock with Portland cement. The popular Florida
use of Lime Rock in small constructions indicated a need for
a research of this nature. This rock, when mined, is a unique
aggregate because it possesses, within limits, both the prop-
erties of the usual fine aggregate, sand, and the coarse aggre-
gate, stone. It is a natural blend of fine and coarse grains.
Proportioning with cement is simplified because only one aggre-
gate is required in the mix.
There are two varieties of limestone in the State of Florida.
The hard rock is tough and has good crushing strength. The
soft rock, though easily friable, has excellent properties and
it is this material which by common usage has been named "Lime
Rock". Since the amount of hard rock commercially available
is small compared to the total amount of soft rock, this investi-
gation has been limited to the latter. It is found in abundance
in the north central to central parts of the state and west to
the gulf.
The soft rock is a compact, cream-white, high calcium lime-
stone (96.0 99.0'/. CaCO.i) and consists of coral and other ma-
rine remains which have been disintegrated by weathering and
erosion. The rock is mostly soft and friable though some hard,
crystalline particles permeate the mass.
It is obtained by open pit mining, by first stripping off the
top soil and sand (see Fig. 2). Dynamite is used to break the
solid mass and the broken material is loaded into cars for trans-
portation to screens to remove the large lumps (over 31"). Lime
Rock requires no washing since it is free of clay and organic im-
purities and is ready for use as aggregate immediately after
screening. These factors are important from the standpoint
of economy because many of the aggregates which are commonly
used must be crushed, washed and screened.
The type of research which is devoted to the study of the

characteristics of any geologic material depends upon the chemi-
cal and physical properties of the material as well as the use
for which it is intended. Since Lime Rock is a highly pure form
of calcium carbonate so its chemical characteristics are fixed
according to the properties of alkaline earth carbonates. These
carbonates find their chief chemical applications as raw material
for lime, as a source of carbon dioxide and as acid neutralizing
agents. There are many specialty applications in industry such
as ground material for pigments, abrasives, fillers and even as
mineral feed for cattle. Since the topic for this bulletin is con-
fined to the application of Lime Rock in concrete, the scope of
the research is limited to the problems encountered in this field.
No attempts have been made to study the application of Lime
Rock concrete to the field of reinforced structures.
Numerous buildings, floors and pavements have been con-
structed in the section of Florida where Lime Rock is abundant.
These installations have shown excellent resistance to disinte-
gration after years of exposure to the weather. Several photo-
graphs are included which show these structures. In the light
of our present knowledge the use of Lime Rock Concrete should
be confined to those installations in which the compressive
strength required does not exceed 1,750 to 2,000 lbs. per square
inch when using a 1 to 7 by volume mix. Other work is being
done to cover more severe conditions.

Fig. 2.-Open pit mining of Florida Lime Rock.

For comparison of the cost of Lime Rock concrete with a
standard concrete as designed by the Testing Laboratory of
the Florida State Highway Department the following informa-
tion is included:
(A) Standard Concrete 1 : 2.2 : 3.2 by volume
Specifications: Modulus of Rupture 650 psi min. 14 days
for concrete


Material Cost:

Compressive Strength, psi 28 days
Min. 3000 Max. 3500
1.5 barrels per cu. yd. of concrete
5.7 gallons of water per sack of cement
Slump inches:
Mmin. 2.0 Max. 3.0
(1) Portland Cement (Fla. P. C. Company) $2.25 per
barrel, $.5625 per sack (1 cu. ft.) (delivered)
(2) Crushed Stone (Fla. Crushed Stone Co.) Grade
No. 2 paving stone 60% to 95% thru 1%" $3.00
to $3.50 per cu. yd. Delivered.
(3) Sand--Type (1)
Retained on '%
No. 4 sieve 0 5
No. 8 0- 15
No. 16 3- 30
No. 30 30-70
No. 50 65-95
No. 100 95- 100
$2.50 to $3.00 per cu. yd. (delivered)

Fig. 2a.-Structure of Soft Lime Rock. Note fossil inclusions.

Calculations of material cost of 1 :2.2 :3.2 concrete
Based on 1 cu. yd. of portland cement
(a) cement = 1 x 27 ($0.5625) = $15.20
(b) sand = 2.2 x $2.75 = 6.05
(c) stone = 3.2:: $3.25 = 10.40
(B) Lime Rock Concrete: 1:5.2 by volume to correspond to same volume
quantities used in the standard concrete.
1:5.2 concrete: Compressive Strength psi 28 day 1800 to 2200
Modulus of Rupture (14 day) 400 psi min.
15.0 gals water/sack cement
1" slump. (max.)
Calculations of Solid Volume 1:5.2 concrete
(a) cement 1x94 = 0.485
3.1 x 62.4
(b) Lime Rock 5.2 x 94 = 3.260
2.4 x 62.4
(c) Water 15 x 8.33 2.000
15 gals. 1 x 62.4 5.745 cu. ft.
27 = 4.7 sacks cemein per cu. yd. concrete
Material Cost (1) Portland Cement (Fla. P. C. Co.) $2.25 per bbl.,
$0.5625 per sk. or cu. ft.
(2) *Lime Rock (delivered for Gainesville Area)
$1.75 per cu. yd.
Calculation of material cost of 1 :5.2 Lime Rock Concrete
Based on 1 cu. yd. of portland cenmelL
(a) cement 1x27 (0.5625) = $15.20
(b) Lime Rock 5.2 (1.75) = 9.10
Cost per sack of cement
Standard Concrete 1 : 2.2 : 3.2 = $1.170
Lime Rock Concrete 1: 5.2 = 0.900
difference $0.270
The Lime Rock concrete, for the same volume ratio of cement,
shows a saving of 23.8% in raw materials. Whenever the
strength of Lime Rock concrete is sufficient this saving in cost
is material.

Materials Used
Soft Lime Rock from several pits in the vicinity of Ocala,
Florida was used throughout except as otherwise indicated in
the bulletin.
Basd on Lime Rock costt of $0.75 per ton plusl 0 52 per tan freight.

Brooksville Stone was used for larger aggregate in regular
Portland cement manufactured by the Florida Portland
Cement Company was used in every test.
Concrete Sand from Lake Interlachen was used as fine aggre-
gate in regular concrete.
Test of Raw Materials
(1) Volumes
The dry rodded weight of Lime Rock per cubic foot was
determined with a 6" x 6" x 6" steel box (1/8 cu. ft.) and found to
average 80 lbs. with exclusion of lumps larger than 3/ inch.
The unit weight of cement was taken at the accepted value
of 94 lbs. per cubic foot.
(2) Moisture
The moisture determination on Lime Rock was made on the
dry basis using the moisture lost from a weighed sample after
drying in an oven at 1000 C. to constant weight. This moisture
was included as part of the mixing water.
Due to the fact that Lime Rock is water absorbent there is
need for careful control of moisture in the field. A field method
to determine moisture content by weighing a properly screened
quantity of Lime Rock was developed and proved to be a satis-
factory solution of the problem. This method is included in
Appendix A (Page 34).
The portland cement was accepted as bone dry and used out
of closed steel bins.
(3) Mechanical Sieve Analysis
Mesh % On % Passing
10 0 100
14 0.5 99.50
48 0.1 99.40
80 6.9 92.50
100 41.5 51.00
200 43.5 7.50
Pan 7.5
Inch % On % Passing
1.0 0.0 100
% 7.5 92.5
% 52.0 40.5
% 30.0 10.5
% 9.0 1.5
Pan 1.5

Preparation of Mixes
The standard method of proportioning by volume was used.
For accuracy all quantities were converted to a weight basis
and carefully blended in a laboratory concrete mixer along with
the amount of mixing water needed to give the proper con-
sistency. The concrete was mixed at least five minutes in every
case unless otherwise specified so as to insure complete wetting
of aggregate and dispersion of cement.
Placing of the Concrete
Standard 3-inch diameter by 6-inch long waterproof, card-
board forms were used for molding the test cylinders. The wet
concrete was rodded unless otherwise specified to remove en-
trapped air, secure well filled forms and prevent particle segre-
gation. Lime Rock concrete does not tend to segregate badly
and mixing water does not bleed out readily, when mixed accord-
ing to directions. However it does entrap air which must be
removed before a well consolidated concrete can be obtained.
The cardboard forms were stripped off after 24 hours and the
cylinder subjected to curing. For more complete information
on mixing and placing see page 13.
Curing of the Concrete
The hydration of concrete is due to chemical reactions be-
tween the water and the portland cement. The hydrated cement
forms a network of crystals which bond the aggregate. Hydra-
tion proceeds continuously over a long period under favorable
temperature and moisture conditions. The object of curing is
to prevent rapid evaporation of the water from the surface
before satisfactory hydration has occurred. The cylinders used
in this investigation were moist cured 7 days, then allowed to
age in the air of the laboratory.
Method of Testing Cylinders
Compressive Strength
Since compressive strength is a standard method of evaluat-
ing concrete all of the comparisons were made on this basis.
Compressive strength is reported as the number of pounds per
square inch necessary to break the concrete cylinder. The
breaking load is read directly from the calibrated balance arm
of the testing machine (Fig. 3) and gives the total pressure
[ 10]

required. These total values are converted to pounds per square
inch by dividing by the area of the cylinder in contact with
the machine surface. These cylinders were tested after 7, 14,
and 28 days in most instances, however some cylinders were
checked also at the end of 90 days and 1 year.
The data under compressive strength were compiled from
tests made on the Riehle Testing Machine which has a maxi-
mum capacity of 50,000 pounds. Each figure in the tables is
an average of at least three breaks made with the machine
operating so that the opposite flat surfaces approached each
other at the rate of 0.125 inches per minute. The cylinder was
supported on a spherical bearing block. All the samples were
capped on both ends with a thin, smooth finish of quick setting
moulding plaster (CaS04) % HO2). This was done in order to
expose a smooth flat surface to the machine face. The samples
were not broken until the plaster was set sufficiently well so
that it would not yield under pressure, thereby giving erroneous
values. The compressive strength results are averages of a
large number of tests. An average deviation of 250 lbs. in
breaking load was used in the computation.

Fig. 3.-Riehle Compression Testing Machine, with capped cylinder
in position for test.

Types of Tests Conducted
The type of tests which are included in this bulletin are
those which contribute most to practical knowledge of the use
of Lime Rock in concrete.
(1) Method of Mixing and Placing
Due to the fact that Lime Rock has very different character-
istics from the usual aggregates employed, a complete descrip-
tion of the proper method of mixing and placing of the wet
aggregate is included along with compressive strength results
secured when the sample is rodded or vibrated.
The plastic nature of the wet concrete made from Lime Rock
requires a special mixing and handling technique in order to
secure best results. A study was made of the action of the con-
crete in the mixer. The problems encountered in placing this
concrete were observed and the best methods of placing recom-
(2) Study of the Changes in Compressive Strength Caused by
Varying the Mixing Water
Due to the fact that Lime Rock is water absorbent the re-
search was directed into an extensive study of the effect of the
Quantity of Mixing Water on the Strength of Hardened Concrete.

Fig. 4.-Broken concrete cylinder, showing particle size
and distribution.
[ 12]

(3) Study of the Changes in Compressive Strength Due to the
Variation of Particle Size in Lime Rock as Aggregate.
The effect of changing the proportions of fine and coarse
particles of Lime Rock was studied and compared with the
naturally blended material.
(4) The effect of Clay on the Compressive Strength
In Lime Rock mining operations, it is frequently difficult
to keep clay and organic impurities from adulterating the
product. A careful study of the effect of contamination was
made and limits set on the amount of clay which the Lime Rock
could contain without having an injurious effect on the com-
pressive strength.
(5) Lime Rock Concrete Cured Under Favorable and Unfavor-
able Conditions
In this section the effect of temperature on the degree of
hydration of Lime Rock is compared with the degree of hydra-
tion secured using other aggregates.
(6) Lime Rock Concrete Made Using All the Factors Observed
in Order to Secure the Best Possible Compressive Strength
This work was conducted in order to confirm observations
on Methods of mixing and properly placing Lime Rock Concrete.
The influence of mixing time was studied in order to determine
its effect on compressive strength.
(7) Abrasion Resistance of Lime Rock Concrete
This investigation is included to illustrate the wearing quality
of a Lime Rock Concrete Slab when subjected to friction pro-
duced by a sliding 8-lb. steel sheet.
Mix 1 :7 by Volume
In order that the very best results be obtained from the use
of Lime Rock as an aggregate for concrete the steps outlined
below must be followed carefully. These steps are the result
of considerable work and experience in the use of Lime Rock
as an aggregate.
Preparation of Aggregate
Screen the Lime Rock through a :H" sieve, retaining only

that material which passes, as larger lumps lower the compres-
sive strength as well as require a longer mixing time to wet the
large particles. If slightly stronger compressive results are
desired the aggregate should be screened through a %" sieve.
Aggregate of larger diameter than 3/4" lowers the compressive
strength considerably as test cylinders broken in the laboratory
show that the breaks are generally thru the larger pieces when
they are present. (See Fig. 4).
Calculation of Proportions
A 1 :7 mix by Volume means that 1 volume of portland
cement is blended with 7 volumes of bone dry Lime Rock. When
concrete is prepared in the field, the 1 :7 volume relationship
can be maintained by using 1 cu. ft. (1 sack) of cement to 7
cu. ft. of Lime Rock corrected for moisture as described on
page 34.
For more accurate work demanding closely controlled condi-
tions the mix should be proportioned by weight. For example
when a 1 :7 dry mix by volume is needed, the weight propor-
tions may be calculated by using 80 lbs. per cu. ft. as the density
of dry Lime Rock and 94 lbs. per cu. ft. as the density of port-
land cement.
Calculations for Changing 1: 7 by Volume
to a weight basis; Basis 100 lb. batch of dry mix:
1 x 94 = 94 Ibs. of cement
7 x 80 = 560 lbs. of bone dry Lime Rock
654 lbs. of mixture
( 04- 654) 100 = 14.37 Ibs. of Portland Cement
(560 654) 100 = 85.63 Ibs. of Lime Rock
100.00 lbs. bone dry mix*
Incorporation of Mixing Water
In making Lime Rock concrete there are several factors that
must be taken into consideration but the proper water content
is most important. Lime Rock concrete must not be placed until
the moisture content is correct. The proper control of mixing
water assures optimum workability and strength. Since Lime
Rock itself absorbs relatively large amounts of water, the ap-
parently dry appearing Lime Rock may vary in water content
by as much as 10% without being detected by the casual ob-
server. It is suggested that when Lime Rock is used the oper-
*To correct for moisture as received refer to page 34.
[ 14]

ator should be carefully instructed on proper method of moisture
control. A procedure for measuring the moisture content of
Lime Rock in the field is included in this bulletin (page 34).
Concrete made, having a slump test of 1" 1/2" gives excellent
results and a mix having that maximum slump should be used
in every case. It is best to add mixing water until a consistency
is obtained which gives this value, and in most cases a 1 : 7 mix
using bone dry Lime Rock requires approximately 16 gals. of
mixing water per sack of cement. This denotes that Lime Rock
absorbs nearly 35% more water than is needed in the usual sand-
gravel concrete of these proportions.
The final strength of concrete depends largely upon the pro-
portion of cement and water used when mixing. Excessive
water not only dilutes the paste and cuts the strength, but causes
segregation. Lime Rock aggregates cannot be handled like the
more or less impenetrable aggregates commonly employed and
cannot be treated as such in mixing operations. Its excellent
flow characteristics and ease of finishing offset special attention
needed in mixing operations.
Time of Mixing
Since Lime Rock is very absorbent and requires time for the
water to completely saturate the particle, the mixer should be
run at least twice as long as is required by the usual hard aggre-
gate. It will be noted that the required slump can be obtained
very quickly with less than the specified amount of water and
the consistency appears to be correct for pouring, but if the
mixer is run several minutes longer the batch becomes drier
than it appeared to be at first. This is due to the fact that the
Lime Rock granule absorbs the mixing water slowly through
its surfaces and into its structure.
Time of mixing increases the compressive strength as can
be seen by reference to tests on this characteristic, page 32, and
best results cannot be obtained unless complete wetting of the
Lime Rock particle takes place. If the Lime Rock Concrete is
placed before being thoroughly mixed, the particles absorb the
water until saturated. This removes water which is needed to
properly hydrate the cement. Improperly wet concrete appar-
ently dries out rapidly due to absorption of water by the aggre-

gate. This will hinder finishing operations on surfaces such as
Appearance of Properly Wet and Mixed Lime Rock Concrete
Lime Rock concrete when properly wet is fatty, pasty, or
sticky and water does not run out easily when the cement is
placed. Concrete having a slump over 11/2" begins to show free
water when it is puddled on a glass plate indicating maximum
aggregate wetting. Observation of the material in the mixer
will show that properly wet Lime Rock concrete has a critical
point where it does not fall apart when tumbling from the mixer
blade, but holds together without breaking up. Any additional
water will cause it to form a slurry and it will run freely. If
too little water is added the material does not form this adherent
mass, but crumbles and breaks up as it falls from the mixer
Curing of Lime Rock Concrete
The strength of Lime Rock concrete can be increased by
keeping it moist during the early curing stages. It is believed,
however, that this is not as important with Lime Rock as with
other aggregates. Lime Rock retains moisture and therefore
helps to prevent rapid drying out before nearly complete hydra-
tion of the cement has occurred.
Method of Placing
The concrete should always be rodded or vibrated when it
is poured into place, so as to remove the entrapped air. Lime
Rock concrete when it contains the proper amount of mixing
water tends to retain air bubbles and unless these bubbles are
removed the concrete is materially weakened. Lime Rock con-
crete is extremely workable and fills crevices and corners nicely
when these directions are closely followed.
(1) Results Obtained Using Various Methods of Mixing and
Placing Lime Rock Concrete
Mix 1: 7 by Volume
Slump 2" 2" 2"
*Gals. of water per sack of
cement ..................... .. ..... 20% 21 22
Method of placing rodded vibrated vibrated
%" rod 3400 rpm. 1750 rpm.
NOTE*: Water is total water including the amount present in the Lime Rock. Mixing
time is approximn tely 5 minutes.

Compreive strength
in Ib.a per uquarp inch
7 day .. .. ................ 518 MAO 02
to day 813 820 082
Smonth ......... ... 197 124R 105R

A series of runs was made in order to determine the effect
of mixing methods on the final strength of this concrete. Little
effect could be observed as long as the percentage composition
of the mix was kept constant. The most convenient method of
combining the aggregate, cement and water proved satisfactory.
For convenience it is best to add the Lime Rock and cement to
the mixer then blend the mixing water in until the proper con-
sistency is attained.
Methods of placing the concrete made very little difference
in compression results whether rodded or vibrated when the
same quantity of mixing water was used. It is necessary that
all the air be displaced and the voids properly filed to secure
maximum strength. It is apparent that excessive mixing water
lowers compressive strength. (See Fig. 5).
(2) Changes i Compresive Strength of Lime Rock Concrete
Caused by Varying the Mixig Water per Sack of Cement

Mix 1 : by Volume
*Gals. of water per sack
of ement .............. ... 12 1 14 8t 16 17 18I
Slump avers e, Inrhe 0 0 0 % 1% 2
Compresivw stnrwnth
lb prr quarry inch
7 day ........ 1043 13651 1to 14OS 12145 812
2S day .................-- 150 1760 1230 1640 172 60 12
3 months .... 2760 1910 220 2530 22 1720

This is the richest mix which was made and good compressive
strengths were secured. The greatest strength was obtained
when 13 or 14 gallons of water per sack of cement were used,
12 gallons per sack gave low strength due to insuffident wetting
of the aggregate. The critical point was reached when between
17 and 18 gallons of water were incorporated. This critical point
can be noted by the sudden decrease in strength when mixing
water is increased from 17 to 181;.. The slumps mrw quite con-
N OTh*: Ws1We to Iaol waltr i*arn dn the ummMt r is tis Lar Ea ucrkL Mwlnl
b m, f~lso iema mIsllnaL

It b6s. 8 ons.

18 16b. 0 o0.

11 Ibs. 8 ozs.

11 Ibs. O ozs.

10 Ibs. 8 ois.

10 Ibs. 0 ozs.

9 Ibs. 8 ozs.

9 Ibs. 0 ozs.

8 1bs. 8 ozs.

8 lb6. 0 ozs.

7 Ibs. 8 oxs,



Fig. 13.-FOR USE
Page 34


t4 25


- 2000

S-____ 3 Mo.o

lOO --- -- -- --\"' ^ ---- --

0 -__ ____-

o 1000 -- ----

0---------------------------------------------------__ ___.

11 12 15 17 19 21
I'. S. (;ill ns p'r Snrk of ('emcnt

sistent. From consideration of both strength and ease of
handling, the optimum amount of mixing water is 161,/ gallons
per sack of cement. (See Fig. 6).

Lime Rock Concrete
Mix 1: 6 by Volume
*Gals. of water per sack
of cement .................................. 15 16 17 18 19 20
Slump inches ............... .............. .. 0 0 3 4'% 8 max
Compressive strength
in lbs. per sq. inch
7 day ............... -.... .........---........--... ... 476 823 901 780 694 623
28 day ................................................. 642 1245 1525 1330 1056 923
3 month ........................................... 1155 2000 1940 1770 1520 1220
1 year ........................................ .. 1065 1830 1930 1630 1298 1093
NOTE*: Water is total water including the amount present in the Lime Rock. Mixing
time is approximately 5 minutes on each test.

The best strength is shown in column 3, Table III (Fig. 7),
where 17 gallons of water were used. The slump increased
rapidly between 17 and 18 showing a critical point when this
quantity of mixing water is used. There is a definite break in
compressive strength after the addition of mixing water in
excess of 18 gallons. An unaccounted for decrease in strength
is to be noted in the year test under air storage. Some tendency
in that direction may be noted under 1 : 9 mix but not a definite
trend as is shown above. Lime Rock concrete in general does
not seem to gain very much after 3 months. Rapid set is a good
characteristic of Lime Rock concrete.

Mix 1 :7 by Volume
*Gals. of water per
sack of cement 16 17 18 19 20 21 22 24 15
average, inches 1 2 2 1% 3% 4 61 9 0
Compressive strength
in lbs. per sq. inch
7 day ...................1325 1275 1060 946 788 625 286 307 476
28 day .....................1782 1712 1938 1530 1400 810 456 453 642
3 month ............... 2400 2320 1857 1845 1560 1156 844 670
NOTE*: Water is total water including the amount present in the Lime Rock. Mixing
time is approximately 5 minutes on each test.
These results are averages of a large number of experimental
runs. Great care was used in making these compilations in order
to secure mean values. The tests entered in table IV are rep-
resentative of the behavior of Lime Rock concrete. A gradual

2500 -

\, .. o.3 Mo.
- 2000
u ___-28 Day

- 1500

- 500

12 13 14 15 16 17 18
(Gallons per Suck of C('ement

increase in slump and decrease in compressive strength is noted
as the mixing water is increased. Best results in this series
were obtained using 16-17 gallons of mixing water per sack of
cement. It is to be noted also that a sharp break in the com-
pressive strength indicates a critical point for this mix between
22 and 23 gallons of water per sack of cement. The safe work-
ing range therefore is from 17 to 20 gallons of water per sack
of cement when the cement lime rock ratio is 1 : 7.
Lime Rock Concrete
Mix 1:9 by Volume
*Gals. water per sack
of cement ............................ 23 24 25 26 27 28 29
Slump, inches .......................... 0 1 1 1% 6% 9% max
Compressive strength
in lbs. per sq. inch
7 day ................................ 592 576 528 490 342 335 765
28 day ........................................ 846 884 805 797 542 538 -
3 month .................................. 1185 1276 1120 1224 850 920 523
1 year ...................................... 1130 1215 1170 1125 911 816 923
NOTE*: Water i total water Including the amount present in the Lime Rock. Mixing
time is approximately 5 minutes.
It was found to be impossible to make compression specimens
for tests on a 1 :9 mix using less water than 23 gallons per
sack of cement. Zero slump is extremely difficult to handle and
place properly. However, it was found and can be seen in
column 2 that best results were obtained at the point where the
concrete becomes plastic. It is to be noted that 1:9 mix requires
23-26 gallons of water if good results are to be obtained. The
same falling off in compression results can be observed here as
was noted in other mixes when the water ratio was increased.
A sharp break and extremely high slump is shown between 26
and 27 gallons per sack. These results are averages of a large
number of tests. The 1 :9 mix gives only 60 to 70% of the
strength of the 1 : 7 mix (Table IV). The saving in dollars for
cement does not justify the loss in strength to make the 1 :9
proportion a practical mixture. (See Fig. 8).
(3) Changes in Compressive Strength Due to the Variation of
Particle Size of Lime Rock Used as Aggregate
(3a) Effect of Variation of Fine Particles on Compressive
Strength of Lime Rock Concrete
Mix 1:7 by Volume


15 16 17 18 19 20
U. S. Gallons per Sack of Cement






*Gals. of water per
sack of cement ........ 18 18 18 18 18 18 18 18
Slump, inches ............. 5 4 4 4 3% 3 4 2
Compressive strength
in lbs. per sq. inch
7 day ............................ 470 525 632 667 654 533 593 598
28 day ........................... 761 810 935 1000 943 928 835 935
3 month ...................... 1155 1410 1610 1500 1387 1480 1435 1495
Fines in mixture % ...... 40 35 30 25 20 15 10 5
NOTE*: Water is total water Including the amount present In the Lime Rock. Mixing
time is approximately I minutes.
Table VI (plotted in Fig. 9) indicates that the best compres-
sive strength with a 1 :7 by volume mix can be obtained with
Lime Rock having fines in the vicinity of 25%. Fines in Lime
Rock are considered a material which passes the 100 mesh
screen. It is to be noted however, that in addition to the amount
of fines the slump must be considered. For best results the
slump should not exceed 11/2" with the optimum amount of fines.
Actual screen tests made on run of the pit Lime Rock show
that 22.5- 25.5% passes the 100 mesh. Since the best results
are attained in the vicinity of 25.0% it is proved that run of
the pit material in regard to fines is satisfactory. It is to be
noted that there is marked decrease in strength between 25
and 40% fines. None of the tests show as good results with
this blended material as can be obtained by properly mixing
and placing the natural run of the pit aggregate.
In certain pits the fines run to 40% and over. In that case
a 1 to 6 or 1 to 5 by volume mix gives better results. It is ad-
visable to make a screen test when making the first run from
a given pit. A later Bulletin will give more details on the
variation of fines.
(3b) Effect of Large Particles on Compressive Strength of Lime
Rock Concrete
Mix 1:7 by Volume
All aggregate through All aggregate through
%" mesh %" mesh
*Gal's of water per sack
of cement ................... 21.4* 20.8*
Slump ................... ......... 1 1" W"
Compressive strength
Ibs. per square inch
2 day ...... ...................... 886 806
7 day .................................. 1180 900
14 day ................................. 1260 1120
Amount of water controlled by slump determination.


U. 8. Gallos per Sack of Cement


- -1 -D- --zt
- - - - - - - -

-_ -, -, -- -





Lime Rock was screened through :/4" and /%" mesh screen
and cylinders were made using the material passing these
screens as aggregate in separate batches. The mixer was run
20-25 minutes so as to determine the wetting of the particles.
Though the Lime Rock appeared to be properly wet and the
proper slump obtained in 3 to 5 minutes, further operation of the
mixer showed a decrease in slump. This indicated that the
Lime Rock particles were absorbing the mixing water slowly,
causing the mix to become dry.
The slump was correct after 15 minutes mixing. The water
was slowly added over this period until this correct consistency
was secured. There was no change in the consistency after 5
minutes additional mixing, indicating a completely wet mix had
been secured. The table shows that good results are obtained
when the time factor is considered. The results are slightly
better if 3/" screenings are used, but from an economical stand-
point there does not seem to be sufficient advantage in screening
out material smaller than %3". The compressive strengths shown
here may be lower than normal due to attrition caused by the
long mixing time.
(4) Effect of Clay on the Compressive Strength of Lime Rock
Mix 1 : 7 by Volume
Varying '; of Clay in Lime Rock Concrete
Slump, inches ....... 2 1% 1' 2 2 1% 1% 2
Gals. of water per
sack of cement 16 16 15 16 19 21 23% 28%
% Clay in Lime Rock
aggregate ................ 0 1 2 3 5 10 15 *Ga. Lime
Rock %
Clay not
Compressive strength
in lbs. per sq. inch
7 day .-.......... 732 1190 1100 1880 732 494 377 300
28 day ..................1130 1450 1450 1380 1130 770 683 470
3 months ................2290 2360 2215 1928 1720 1595 1350 813
Reported to contain 15 to 20'; clay.
Lime Rock for concrete aggregate must be essentially free
from clay because it lowers the compressive strength of the con-
crete when present in amounts exceeding 2%7. The results in-

2500 1III-I-- Ii I1

10 15 20 25
Per Cent Lime Rock through 100 Mesh





eluded in Table VIII and plotted in Fig. 10 were obtained by
adding increasingly larger quantities of pure koalin to Lime Rock
aggregate of clay free variety. Florida Lime Rock runs over
96% calcium carbonate on a moisture free basis. Kaolin was
used because of the fact that it is uniform in composition whereas
ordinary clay varies considerably in composition. Cylinders
which were molded with 5% or more kaolin showed a tendency
to crack when the molds were removed in 24 hours after mixing.
(5) Lime Rock Concrete Cured Under Favorable and Unfavor-
able Conditions
Mixes Tested
A-Cement, sand, gravel (1:2: :41) 7% gals. water/sack cement
B-Cement, sand (1-7) 17 gals. water/sack cement
C Cement, lime rock (1 : 7) 18 gals. water/sack cement
Slump 1" for all mixes

Compression Tests Ibs. per square inch
Days in curing rooms ..........-......--- 4 10 18 28
at 4' F.
A ._... ...... --- ---------- 304 516 584 630
B -- 70 141 151 200
C ........... --------- -- 409 690 685 680
at 37' F.
A ...... ... --------------- 424 1060 1270 1250
B ........ ------------- ---- 153 282 388 496
C ..-----.. .--- 492 1060 1235 1240
at 68' F.
A- ... ....... .. ------- 720 1080 1990 2000
B- .........159 482 500 646
C ...-...... ................ .. ..---... 572 1085 1344 1750

These tests were run in order to obtain information as to the
ability of Lime Rock concrete to withstand severe cold weather
during the early curing period and to secure data on the retard-
ing effect cold weather has on the hydration rate. A comparison
with commonly used aggregate is included in the report. The
samples were allowed to set 24 hours before they were placed in
the constant temperature rooms. Frozen cylinders were thawed
before compression tests were made.
A general observation of these data will show that Lime
Rock concrete gives better strength than the other mixes at
freezing temperatures. At room temperature it does not attain
quite the strength of cement, sand, gravel mix. It is superior
to the sand cement mortar throughout the entire test.




S1 2 5 10

Per Cent Clay added to Aggregate
? 1000 -- -- -- ^-

---- ^- ---


(6) Lime Rock Concrete Made, Using All the Factors Observed
in Tests in Order to Secure the Best Possible Compressive
(6a) Placed by Rodding

Mix 1: 7 by Volume
Slum p, inches ..........-- ....-- ......... --- --- ..- ...... 1
Mixing water per sack of cement .................. 16
Compressive strength
lbs. per sq. inch
7 day ......-...-........ .... ............. 875
14 day --.... ----- ..... .... .. .....--. .. ................ 1570
28 day .....-..--... ----....--- -- ---- 1785

A 1-7 mix was made using the correct amount of mixing
water and time of mixing as explained on page 34. The cylinders
were placed by rodding to remove entrapped air. These results
confirm the statement made in the introduction that Lime Rock
concrete aggregate at the present should be confined to those
types of installations which do not require a compressive
strength greater than 1750 to 2000 llbs. per square inch, using
the 1-7 mix.
The cylinders used in this test were cured in the dry air of
the laboratory after a seven day moist cure.
For other results using this same mix refer to Table IV. In
Table IV 28 day tests duplicate the results of Table X, while
after 3 months cure, values in excess of 2000 lbs. per square inch
were obtained.
(6b) Placed by Vibrating Lime Rock Concrete

Mix 1:4 by Volume
Slump 0" 11 gals. water per sack cement
Compressive strength (lbs. per square inch)
7 day .................. ........... .. .. ............... .. 1360
14 day ........ ... --................ ... ... .. 2500
28 day ....... ....... .....-- -......... ..... 2000
Compression results obtained by vibrating the cylinders 30
seconds are shown in Table XII. An almost complete absence of
entrapped air bubbles in the broken cylinders indicated that
beneficial results can be obtained when the concrete is placed
by vibrating. These values agree well with similar tests in
which the wet concrete is rodded to remove trapped air.

(6c) Influence of Mixing Time on Compression Strength
Mix 1:7 by Volume
2" slump. 16 gals. mixing water per sack of cement
Compressive strength
lbs. per sq. inch
3 mins. 6 mins. 12 mins. 20 mins. 30 m;ns.
7 day .......... .... ........ 610 622 770 680 705
14 day ............................. 792 970 970 831 1030
28 day ............................ 1020 1030 1310 1180 1130
Compressive strength increased with increased mixing time
up to 12 minutes. These tests indicate that adequate mixing
cannot be obtained in less time in the small laboratory mixer.
Excess water giving a 2" slump was used to be sure that suffi-
cient water was present and that this test was merely measuring
the rate of water absorption. Large commercial mixers will
reduce this time by giving more violent mixing action.
The concrete must be mixed long enough to disperse the
cement uniformly throughout the mass of Lime Rock particles.
Also sufficient time must be allowed for the extremely absorbent
Lime Rock particles to become completely wet.
(7) Abrasion Resistance of Cement Stabilized Lime Rock
Mix by Volume Average Abrasion, mm./hr.
1-5 Cement-Sand ........... ... .... .. 3.0
1-7 Cement-Lime Rock ..... ... 0.5
1-14 Cement-Lime Rock ....... 3.0
1-20 Cement-Lime Rock ...... 3.5
1-30 Cement-Lime Rock ... 4.5
Lime Rock-No Cement .... Greater than 6.0
Disintegrated by
breaking apart.
Abrasive Resistance of the Lime Rock Concrete. All samples
used in this experiment were compacted to maximum density
when placing. An abrasion testing machine (Fig. 11) was built
for these tests. An eight pound reciprocating flat steel sheet,
/% of an inch thick and 6" wide by 12" long was used for sliding
uniformly without pressure over the surface of the treated Lime
Rock. The machine was operated at 15 strokes per minute.
The rate of abrasion was measured in millimeters per hour.
The samples were molded in wooden forms to give the correct
size for the testing machine. They were allowed to cure 14
days before being tested.

It is to be noted that 1-14 cement Lime Rock is equally to 1-5
sand cement in abrasion resistance and 1-7 Cement-Lime Rock
is superior. When the cement content falls below 1-14 the
abrasion resistance drops off rapidly.

Fig. 11.-Abrasion Testing Machine.

Fig. 12.-Abrasion tested samples. Left, 1-5 sand cement; right, 1-14
lime rock cement, after the same abrasion test showing the same wear.
[33 ]

Results on the use of Lime Rock as a concrete aggregate
show that it has some very definite advantages in certain ranges
and uses, but it also possesses certain limitations which should
be clearly understood. In the leaner ratio, such as, 1 part of
cement to 7 parts of aggregate by volume, Lime Rock shows a
very definite advantage in increased strength over the use of
sand and flint rock aggregates of the same volume ratio. In
that range when poured on commercial jobs in the field, Lime
Rock concrete can be expected to develop a compressive strength
of 1750 to 2000 Ibs. per square inch when properly made.
Excellent mixing water retention and exceptional workability
without the addition of special agents and chemicals are useful
properties of Lime Rock aggregate. In the wet state Lime Rock
concrete possesses excellent cohesiveness and plasticity and
segregation is no problem if excessive quantities of free water
are not present. The desirability of having a definite consistency
and its effect on ultimate strength was explained fully under
"Methods of Mixing and Placing Lime Rock Concrete". The
research established the proper methods of incorporating the
mixing water and the optimum quantity of water to use in each
mix was selected and recommended.
Since Lime Rock concrete must be placed when the moisture
content is such that the material does not flow freely, the ques-
tion of air bubbles and voids becomes most important. Good
tamping and careful attention to the filling of the forms will
produce a 28 day strength of between 1750 and 2000 Ibs. per
square inch in a 1-7 mix. In the laboratory by careful moisture
control, slump measurement, and intensive vibrating of the forms
it is possible to bring the strength up several hundred pounds
above these values.
Field Test for Approximation of Moisture in Lime Rock
In using Florida Lime Rock as a concrete aggregate, great
care has to be taken to insure that the proper amount of water
is used. It has been shown that the ultimate strength of the
concrete may vary as much as 100% by using improper amounts
of water, keeping everything else the same.

Unlike other common aggregates, Lime Rock absorbs con-
siderable amounts of water without appearing wet to the eye
or touch. In damp weather the Lime Rock as received may
contain almost 15% water by weight and in very dry weather,
go as low as 1 7 in water content. If the same amount of added
water were used in making concrete in the two cases mentioned
above, the strength of the two concretes might vary by as much
as 25%.
In order to insure that the proper water content will be used
in the concrete mixer, this simple field test for the moisture
content is proposed. It is believed that this test will determine
the water content within 1% of the true value.
Weighing Box
6" x 6" x 6" water tight, open end box made of 1/8" thick
sheet steel- total volume 1/8 cu. ft.
Mixing Slab
18" x 18" glass, steel or other moisture impenetrable surface.
Rough weight pounds and ounces from 1.0 lbs. to 50.0 lbs.
6" x6" 3%" mesh wire screen.
Plot showing wet weight of Lime Rock screened through a
3/" mesh which box will hold as moisture content varies from
dry lime rock to point where free water appears. (See Fig. 13
Pages 18 and 19).
Wet Appearance Lime Rock ............. 20.0 to 23.0% moisture
Damp Appearance Lime Rock .....-... 13.0 to 20.0% moisture
Dry Appearance Lime Rock ........-...... 1.0 to 13.0% moisture
Procedure for Determining Moisture Content of Lime Rock
1. Screen 10 lbs. of a representative sample of the lime rock
through the 3%" mesh screen onto the mixing slab.
2. If the sample appears DAMP or WET as shown on the
table above do not add any more water. Place the "/8 screen
over the 6" x 6" box. Then pour the lime rock sample (from

1. above) through the %" screen, rubbing the lime rock through
the screen with the hand and without jarring or shaking the
box, until the box is full. Remove the screen and strike off any
excess lime rock with a straight edge, so that the lime rock fills
the box exactly without packing or tamping.
Weigh the box full of lime rock, recording the weight to the
nearest ounce. Empty the lime rock onto the mixing slab and
re-weigh the empty box in the nearest ounce. The difference
between the two weights is the Weight of the Sample.
3. Refer to the curve (see Pages 18 and 19). The weights
appear on the left hand vertical column. With a straight edge
placed horizontally at the weight, make a dot at the intersection
of the straight edge with the curve. Then measure with a
straight edge vertically from the dot to the bottom of the page.
The number at the bottom of the page gives the water content
in % by weight. If the number is 11% or less, proceed with
(4) below. If the number is more than 11% proceed to (5)
4. To the 10-lb. sample, add exactly 18 ounces of water by
weight (or by volume). Mix the water thoroughly into the
sample with a trowel or a steel rod. The sample now contains
exactly 10% extra water. Repeat (2) and (3) above. Subtract
10 from the water content to get the true per cent water content.
5. Put the original sample aside. Repeat the whole test
with another 10-lb. sample of the lime rock. If the two tests
check within 1% the results are the true water content. If they
do not check, poor sampling or carelessness in weighing are the
cause. Repeat until two good checks within 1% are obtained.

[36 ]


As long as the supply is adequate, copies of available publi-
cations are free for general distribution. Address all requests
to: The Director, Engineering and Industrial Experiment Sta-
tion, University of Florida, Gainesville, Florida.

No. 1 "The Mapping Situation in Florida", by William L. Sawyer.
No. 2 "The Electrical Industry in Florida", by John W. Wilson.
No. 3 "The Locating of Tropical Storms by Means of Associated
Static", by Joseph Weil and Wayne Mason.
No. 4 "Study of Beach Conditions at Daytona Beach, Florida,
and Vicinity", by W. W. Fineren.
No. 5 "Climatic Data for the Design and Operation of Air Con-
ditioning Systems in Florida", by N. C. Ebaugh and
S. P. Goethe.
No. 6 "On Static Emanating from Six Tropical Storms and its
Use in Locating the Position of the Disturbance", by
S. P. Sashoff and Joseph Weil.
No. 7* "Lime Rock Concrete Part 1", by Harry H. Houston
and Ralph A. Morgen.

No. 1* Heats of Solution of the System Sulfur Trioxide and
Water, by Ralph A. Morgen.
No. 2* The Useful Life of Pyro-Meta and Tetraphosphate, by
Ralph A. Morgen and Robert L. Swoope.

* Not printed with State funds.