TP-4. REFINED TAR FOR CONSTRUCTION. 



General. The refined tar shall be homogeneous and free from water. 



Physical and It shall meet the following requirements: 



Ssr^ P"^**!*- 1. Specific gravity 25V25° C. (77V77° F.) 1.200 to 1.250 



2. Float test at 50° C. (122° F.) 120 sec. to 150 sec. 



3. Total distillate by weight: 



To 170° C. (338° F.) not more than 1.0 per cent 



To 270° C. (518° F.) not' more than 10.0 per cent 



To 300° C. (572° F.) not more than 20.0 per cent 



a. Melting point of residue_not more than 65° C. (149° F. ) 



4. Total bitumen (soluble in carbon disulphide) 80% to 97% 



Methods of test- 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 tests, A. S. T. SI. Standard Test D20-16. 



a. Melting point, A. S. T. M. Tentative Standard D36- 

 16 T, Proc. A. S. T. M. 1916, p. 549. 



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



314, p. 25. 



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

 struction of bituminous macadam or one size stone bituminous 

 concrete in the northern United States. It is intended to cover 

 refined gas-house or coke-oven tar. 



In bituminous macadam construction it should be applied in 

 the manner outlined under Specification TP-2. 



One-size stone bituminous concrete contemplates a mixture of 

 the tar with a crusher product passing a IJ-inch screen and re- 

 tained upon a one-half-inch screen. The tar should be heated to 

 a temperature of from 225° F. to 275° F. and the crushed stone 

 to a temperature of from 150° F. to 250° F. before mixing. The 

 mixture should contain from 5 per cent to 7 per cent bitumen, 

 and will vary within these limits with the character of the rock 

 and the exact grading of the aggregate. The hot mixture should 

 be deposited in a uniform layer over a concrete or well compacted 

 broken stone or gravel foundation to such depth that it will yield 

 a uniform layer 2 inches in thickness after thorough rolling. 

 A seal coat of the same tar or of hot asphalt (Specification OA-6) 

 should then be applied at the rate of 0.4 to 0.6 gallon per square 

 yard and covered with a sufficient amount of stone chips to just 

 absorb the excess bitumen. Roads of this character may be main- 

 tained with tar surface treatments, using the materials and 

 methods given under Specifications TC-1, TC— 2, or TH-1. Such 

 maintenance treatments should be applied whenever the wear 

 comes directly upon the wearing-course rock. 

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