.-.. UNITED STATES ATOMIC ENERGY COMMISSION
TREATING CONCRETE SURFACES WITH
Albert E. Salo
May 18, 1955
University of California
L Technical Information Service, Oak Ridge, Tennessee
Subject Category, CHEMISTRY.
Work performed under Contract No. W-7405-eng-48.
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TREATING CONCRETE SURFACES WITH PARAFFIN*
By Albert E. Salo
It is difficult or impossible to remove radioactive contamination from ordinary concrete
surfaces. A penetrating application of paraffin, however, seals the pores of the surface and
makes decontamination relatively easy because it reduces absorption of liquids that might
carry radioactivity. Molten paraffin (mp 1250F) is applied to a clean concrete surface that has
been heated to about 500F. Penetration depths of 1/4 inch are usual, but penetration may range
up to '/4 inch. Pore spaces in the concrete are sealed when the paraffin cools.
The concrete surface is prepared by acid etching and wire brushing. A thorough rinse with
running water is followed by a drying period of at least four days. Batteries of infrared lamps
may be used to help the drying process.
In melting the paraffin, provisions should be made to conduct fumes away and to extinguish
any flash flames. Probability of flashing can be reduced if an electric hotplate is used in pref-
erence to an open flame, and if the liquid temperature is kept below 2000F.
A wide-tip oxyacetylene torch is used to heat the concrete. Great care must be taken in
applying the flame slowly and evenly. Areas of 5 to 10 square feet are heated at one time. The
torch operator should be protected against the possibility of spelling particles by wearing a
face shield and heavy clothing. Molten paraffin is brushed on the heated section until no more
absorption takes place. Paraffin requirement is approximately 0.1 pound per square foot.
A layer of paraffin more than a few mils thick on the surface is both unnecessary and un-
desirable. Protection against possible radioactive contamination is provided by the paraffin
that is absorbed into the concrete, not that which remains on the surface. An excess on the
surface makes floors slippery and dangerous.
Depth of penetration can be checked by the use of concrete test blocks, similar in texture
and mix to the surface to be treated. After treatment the test block may be fractured with a
hammer and chisel. The penetration line will usually be clearly discernible. Fig. 1 shows a
typical cross section of a treated and fractured test block. The dark band at the top of the
piece indicates how far the paraffin has penetrated into the block from application at the top.
The band is wider at the left because in this area penetration also took place through the side
surface. The dark spot on the right of the face and slightly below the surface penetration line
indicates where a small amount of paraffin penetrated through a fissure into the underlying
body of concrete.
Fig. 2 shows a stairway that has been treated with paraffin in the manner described. This
work was done under the auspices of the U. S. Atomic Energy Commission.
*Permission for publication of this information in whole or in part is granted by the author
and the University of California Radiation Laboratory operated for the United States Atomic
Fig. 1 -Treating concrete with paraffin.
Fig. 2- Treating concrete with paraffin.
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