18 



BITLLETIX 704, U. S. DEPARTMENT OF AGEICULTyEE. 



placed upon a cement concrete foundation so as to produce, after 

 rolling, a wearing course 2 iuclies in depth. A seal coat of bitu- 

 minous material should then be applied and covered with pea 

 gravel in suihcieut quantity to take up all excess of bitumen. 



Such roads may be maintained with surface treatments of bitu- 

 minous material, covered with material conforming to Specifica- 

 tion RS-2. 



SPECIFICATION SgW 2. 



Slag for Water-Bound Base. 



General. 



Physical 

 Properties. 



Screenings. 



Coarse Slag. 



Methods of 

 Testing. 



The broken slag shall consist of angular fragments, reasonably uniform 

 in density and quality, free from metallic iron, thin or elongated pieces, 

 dirt, or other objectionable matter. 



The slag shall meet the following requirements : 



Weight in pounds per cubic foot, each size specified, not less than_ 70 

 French coefficient of wear, not less than 5- 



That portion of the product of the crusher, including the dust of 

 fracture, which, when tested by means of laboratory screens, will meet 

 the following requirements : 



Per cent. 



Passing 1-inch screen, not less than 95 



Total passing J-inch screen 40 to 80 



That portion of the product of the crusher, which, when tested by 

 means of laboratory screens, will meet the following requirements : 



Per cent. 



Passing 3-inch screen, not less than 95 



Total passing 2-inch screen 25 to 75 



Retained on 1-inch screen, not less than 85 



The tests of the physical properties and sizes of the slag shall be made 

 in accordance with the following methods : 



1. Weight per Cubic Foot, U. S. Department of Agriculture Bulletin 



555, p. 32 (6). 



2. French Coefficient of Wear, TJ. S. Department of Agriculture Bulletin 



347, p. 5. 



3. Grading, U. S. Department of Agriculture Bulletin 555, p. 32 (8). 



This specification provides primarily for slag to be used in the 

 construction of a water-bound base upon which some higher type 

 of wearing course will be placed, preferably after the base has 

 been finally compacted by traffic. For a light traffic road it may 

 also serve for both foundation and wearing course, provided the 

 thickness of each is not less than 4 inches. 



