TC-2. TAR FOR COLD APPLICATION. 



General. The tar shall be homogeneous. 



Physical and It shall meet the following requirements: 



ert™s.*"'^ ^''""' 1- Specific gravity 25V25° C. (77V77° F.) 1.100 to 1.140 



2. Specific viscosity at 40° C. (104° F.) 2.5 to 35 



3. Total distillate by weight: 



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



To 270° C. (518° F.) not more than 25.0 per cent 



To 300° C. (572° F.) not more than 35.0 per cent 



Methods of test- 4. Total bitumen (soluble in carbon disulphide) 95% tolOO% 



°^' Tests of the physical and chemical properties of the tar shall 



be made in accordance with the following methods : 



1. Specific gravity, Department of Agriculture Bulletin 314, 



p. 4. 



2. Specific 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 primarily for a material to be used 

 In the surface treatment of macadam, gravel, or shell roads to 

 form a thin wearing mat or carpet which may be built up by sub- 

 sequent maintenance treatment of either the same type of mate- 

 rial or a heavier product (Specification TH-1). It may also be 

 used for maintenance of tar macadam or tar concrete roads, for 

 which purpose it is considered preferable to specification TC-1. 

 The specification is intended to cover water-gas tar and low car- 

 bon coke-oven tar products. 



A successful treatment requires that the road surface shall be 

 in a good state of repair, well consolidated, free from holes or 

 depressions, and thoroughly swept for the removal of dust and 

 detritus before the application is made. Newly constructed or 

 reconstructed roads should be permitted to consolidate under 

 traffic before the tar is applied. The tar may usually be applied 

 without heating excepting when cold weather renders it too vis- 

 cous to distribute properly. The initial application should be 

 made by means of a pressure distributor at the rate of from one- 

 third to one-half gallon per square yard. It should be covered 

 with a uniform layer of dustless broken stone all of which will 

 pass a one-half or three-quarter inch laboratory screen or pea 

 gravel, which will pass a one-half inch laboratory screen in an 

 amount just sufficient to absorb the bitumen and to prevent the 

 surface from picking up under traffic. Subsequent applications 

 may be made by a pressure distributor or by brooming the tar 

 uniformly over the road surface. From one-tenth to one-fifth gal- 

 Ion per square yard will usually prove sufficient, and this may be 

 covered with coarse sand or stone chips which will pass a one-half 

 inch laboratory screen. Under favorable conditions a treatment 

 should last throughout at least one season. 

 38 



