SPECIFICATIOlSrS FOR NONBITUMINOUS ROAD MATERIALS. 11 



Tests of the size or mechanical analysis of broken stone, sand, and Methods of 

 mineral filler shall be made in accordance with the following methods : Testing. 



1. Size of broken stone, U. S. Department of Agriculture Bulletin 555, 



p. 32. 



2. Mechanical analysis of sand and mineral filler, TJ. S. Department of 



Agriculture Bulletin 555, p. 33. 



3. Grading of total mineral aggregate, U. S. Department of Agricul- 



ture Bulletin 555, pp. 32 and 33. 



This specification is intended to cover the mineral constituents 

 and grading for bituminous concrete of a modified Topeiia, or 

 stone-filled, sheet asphalt type. It is so drawn that from 10 to 50 

 per cent of broken stone will be required and the mixture of very 

 fine broken stone and sand will possess a satisfactory sheet asphalt 

 grading. Such an aggregate will carry from 7 to 11 per cent of 

 bitumen. It should preferably be placed upon a cement concrete 

 foundation to a compacted depth of 2 inches. No seal coat will 

 ordinarily be required, and maintenance should consist only in 

 patching with bituminous concrete until it is necessary to replace 

 the entire wearing course. 



SPECIFICATION RBC-4. 



Broken Stone, Sand, and Filler for Binder Course <md Sheet Asphalt 

 Wearmg Course. 



BROKEN STONE FOR BINDER COURSE. 



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

 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, and when tested all of the broken stone shall 

 pass a 1-inch laboratory screen. 



The stone shall meet the following requirement: Physical 



Toughness, not less than 8 



SAND FOR BINDER COURSE. 



The sand shall be composed of sound durable stone particles, free from General. 

 a coating of clay and loam, which when tested shall all pass a J-inch 

 laboratory screen. 



TOTAL MINERAL AGGREGATE FOR BINDER COURSE. 



The total mineral aggregate shall consist of a uniform mixture of the General. 

 broken stone and sand, the required grading of each being such as to pro- 

 duce, when properly proportioned, a mixture conforming to the following 

 limitations for grading. The exact proportion of each constituent pro- 

 ducing a mineral aggregate within these limitations shall be as directed 

 by the engineer. 



When tested by means of laboratory screens and sieves the total min- Grading. 

 eral aggregate shall meet the following requirements : 



Per cent. 



Passing 1-inch and retained on J-inch screen 15 to 65 



Passing |-inch screen and retained on 10-mesh sieve 20 to 50 



Passing 10-mesh sieve . 15 to 35 



