General. 



FhyBical and 

 chemical prop- 

 erties. 



Methods of test- 

 ing. 



TH-1. REFINED TAR FOR HOT APPLICATION. 



The refined tar shall be homogeneous and free from water. 

 It shall meet the following requirements : 



1. Specific gravity 25V25°C. (77V77°F.)__not less than 1.130 



2. Float test at 32°C. (90°F.) 60 sec. to 150 sec. 



3. Total distillate by weight : 



To 170°C. (338°F.) not more than 1 per cent 



To 270°C. (518°F.) not more than 15 per cent 



To 300°C. (572°F.) not more than 25 per cent 



4. Total bitumen (soluble in carbon disulphide), 



not less than 85 per cent 



Tests of the physical and chemical properties of the refined 



tar shall be made in accordance with the following methods : 



1. Specific gravity, U. S. Department of Agriculture Bulletin 



314, p. 5. 



2. Float test, U. S. Department of Agriculture Bulletin 



314, p. 9. 



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



4. Total bitumen, U. S. Department of Agi-iculture Bulletin 



314, p 25. 



This specification provides primarily for a material to be used 

 in the surface treatment of macadam, gravel, or shell roads, either 

 with or without a primer coat (Specification TC~1) to form a 

 wearing mat or carpet. A primer coat is particularly desirable on 

 gravel or shell roads. It may also be used for the maintenance 

 of tar macadam or tar concrete roads. The specification is in- 

 tended to cover gas-house, coke-oven, and water-gas 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, if a primer coat has not 

 already been applied. Newly constructed and reconstructed roads 

 should be permitted to consolidate under traffic before the tar is 

 applied. The tar should be heated to a temperature of 200° F. 

 to 250° F. before applying, and the 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 1-inch 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 application may be 

 made by a pressure distributor or by brooming the tar uniformly 

 over the road surface. From one-tenth to one-fifth gallon per 

 square yard will usually prove sufficient, and this may be covered 

 with coarse sand or stone chips which will pass a half-inch lab- 

 oratory screen. Under favorable conditions with occasional patch- 

 ing of any breaks in the surface a treatment should last for 

 several years. 



