BULLETIX 704, U. S. DEPARTMENT OF AGRICULTURE. 



of 2 inches specitied for the wearing course is on the basis of a 

 course 2^ to 3 inches in thickness after consolidation. The chips 

 should be used to fill the surface voids after the first application of 

 bituminous material has been made and also as a cover for the sec- 

 ond application or seal coat. Roads of this type may be maintained 

 with surface treatments of bituminous material, covered with ma- 

 terial conforming to Specification RS-1 or RS-2. 



SPECIFICATION RBC-1. 



General. 



Physical 

 Properties. 



Chips. 



Aggregate. 



Methods of 

 Testing. 



Broken Stone for One-size Stone Bituminous Concrete Wearing Course. 



The broken stone shall consist of angular fragments of rock, excluding 

 schist, shale, and slate, free from thin or elongated pieces, soft or dis- 

 integrated stone, dirt, or other objectionable matter, occurring either 

 free or as a coating on the stone. 



The stone shall meet the following requirements : 



French coefficient of wear, not less than 8 



Todghness, not less than S 



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

 means of laboratorj' screens will meet the following requirements : 



Per cent. 



Passing J-inch screen, not less than 95 



Retained on J-ineh screen, not less than 85 



That portion of the product of the crusher 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 i-inch screen , 25 to 75 



Retained on i-inch screen, not less than 85 



Tests of the physical properties of the rock and of the sizes of 

 broken-stone products shall be made in accordance with the following 

 methods : 



1. French coefficient of wear, U. S. Department of Agriculture Bulletin 



347, p. 5. 



2. Toughness, U. S. Department of Agriculture Bulletin 347, p. 15. 



3. Size, U. S. Department of Agriculture Bulletin 555, p. 32. 



This specification is intended to cover stone to be used in the 

 construction of a bituminous concrete wearing course and seal 

 coat. The broken stone aggregate for the concrete proper is a 

 single size of crusher product with no exact grading limitations. 

 It may therefore produce what is commonly known as an open 

 mix, and will carry from 5 to 7 per cent bitumen. Such mixture 

 may be placed on a well-compacted broken stone or gravel founda- 

 tion or a cement-concrete foundation so as to produce after rolling 

 a wearing course 2 inches in depth. A seal coat of bituminous 

 material should then be applied and covered with chips in 

 sufficient quantity to take up all excess of bitumen. Such roads 

 may be maintained with surface treatments of bituminous mate- 

 i-ials, covered with material conforming to Specification RS-2, 



