16 BULLETIN 691, U. S. DEPARTMENT OF AGRICULTURE. 



325° F., and the mineral aggregate to a temperature of from 

 250° F., to 300° F., before mixing. The mixture should contain 

 from 6% to 8% 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 to 2^ inches in 

 thickness after thorough rolling. A seal coat of the hot oil 

 asphalt 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 maintained with oil surface treatments using the materials 

 and methods given under Specifications OC-2 or OH-1. The 

 latter is usually to be preferred. Such maintenance treatments 

 should be applied whenever the wear comes directly upon the 

 wearing course rock. 



