10 



BULLETIN" 704, U. S. DEPARTMENT OF AGEICULTUBE. 



SO as to produce, after rolling, a wearing course 2 inches in depth. 

 A seal coat of bituminous material should then be applied and cov- 

 ered with chips in sufficient quantity to take up all excess of bitu- 

 men. Such roads may be maintained with surface treatments of 

 bituminous material, covered with material conforming to Speci- 

 fication RS-2. 



General. 



Size. 



General. 



Size. 



SPECIFICATION RBC-3. 



Broken Stone, Sand, and Filler for Fine Agoi'^tJO'te Bituminous Concrete 

 Wearing Course. 



BROKEN STONE. 



The broken stone shall consist of angulai- 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. 



It shall be that product of the crusher which, when tested by means 

 of laboratory screens, will meet the following requirements : 



Per cent. 



Passing J-inch screen, not less than — 95 



Retained on i-inch screen, not less than 20 



SAND. 



The sand shall be composed of sound durable-stone particles, free 

 from a coating of clay or loam. 



When tested by means of laboratory screens the sand shall meet the 

 following requirements : 



Per cent. 



Passing J-inch screen 100 



Retained on 200-mesh sieve, not less than 90 



MINERAL FILLER. 



General. 



Fineness. 



The mineral filler shall consist of limestone, dust, dolomite dust, 

 Portland cement, or natural cement. It shall be free from foreign or 

 other objectionable material. 



When tested by means of laboratory sieves, the mineral filler shall 

 meet the following requirements : 



Per cent. 



Passing .30-mesh sieve 100 



Total passing 200-mesh sieve, not less than 65 



TOTAL MINERAL AGGREGATE. 



Genei-al. 



Grading. 



The total mineral aggregate shall consist of a unifoi-m mixture of 

 the broken stone, sand, and mineral filler, the required grading of each 

 being such as to produce, when properly proportioned, a mixture con- 

 forming to the following limitations for grading. The exact propor- 

 tion of each constituent producing a total mineral aggregate within 

 these limitations shall be as directed by the engineer. 



When tested by means of laboratory screens and sieves the total 

 min(,'ral aggregate shall meet the following requirements : 



Per cent. 



Passing J-inch and retained on J-inch screen 5 to 10 



I'assing .Vinch screen and retained on 10-mesh sieve 11 to 25 



Passing 10-mesh and retained on 40-niesh sieve 7 to 25 



Passing 40-mesh and retained on 80-mosh sieve 11 to .16 



Passing 80-mosh and retained on 200-mesh sieve 10 to 25 



Passing 200-mesh sieve 5 to 11 



