TC-3. TAR FOR COLD PATCHING. 



General. 



The tar shall be homogeneous. 



It shall meet the following requirements: Physical and 



„ , „ „ , „ chemical prop- 



1. Specific gravity 25V25° C. (77V77=' F.) 1.100 to 1.200 erties. 



2. Specific viscosity at 40° C. (104° F.) 40 to 70 



3. Total distillate by weight : 



To 170° C. (338° F.) not less than 2.0 per cent 



To 270° C. (518° F.) 15 to 25 per cent 



To 300° C. (572° F.) not more than 30.0 per cent 



4. Total bitumen (soluble in carbon disulphide), 



not less than 80% 

 Tests of the physical and chemical properties of the tar shall be Methods of test- 

 made in accordance with the following methods : 



1. Specific gravity, Department of Agriculture Bulletin 314, 



p. 4. 



2. Spjciflc viscosity (on first -50 c. c), U. S. Department of 



Agriculture Bulletin 314, p. 7. 



3. Distillation test, A. S. T. M. Standard Test D 20-16. 



4. Total bitumen, U. S. Department of Agriculture Bulletin 



314, p. 25. 



This specification provides for a material to be used in the re- 

 pair of surface breaks, holes and depressions in bituminous-bound 

 and surface-treated roads. It is intended to cover preparations 

 consisting of gas-house, coke-oven, or water-gas tars or pitches 

 which have been rendered sufficiently fluid by the addition of 

 distillates to enable them to be handled without heating. 



For surface breaks and shallow depressions or those which in 

 general do not exceed one-half inch in depth, a patch may be 

 made by painting the bottom of the depression with the tar, and 

 scattering over it a sufficient amount of stone chips to fill the 

 depression. 



In repairing deeper depressions and holes, the old material 

 should be removed to yield a clean bottom. The sides of the hole 

 should be cut, approximately vertical. A mixture of graded broken 

 stone with just a sufficient amount of tar to thoroughly coat each 

 particle should be prepared, and firmly tamped into the hole to 

 form a neat patch in the surface. A thin layer of sand or screen- 

 ings over the patch will prevent it from picking up under traffic. 



39 



