General. 
Physical 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 25°/25°C. (77°/77°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 C. (518°F.) not more than 15 per cent 
To 300°C. (572 C 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 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, 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. 
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