SPECIFICATIONS FOR NONBITUMINOUS KOAD MATERIALS. 17 



In maintaining roads of this type, material as nearly the same 

 as that composing the road surface should be used. In patching, 

 care sTiould be taken that the finished surface after consolidation 

 is smooth and continuous. 



SPECIFICATION GBC-2. 



Gravel, Band, and Filler for Coarse Aggregate Bituminous Concrete 

 Wearing Course. 



GRAVEL. 



The gravel shall be composed of sound, hard, durable fragments of General. 

 rock of high resistance to abrasion and shall contain no particles of 

 shale, slate, coal, or other materials which easily disintegrate. It shall 

 be free from vegetable or other deleterious matter, and shall contain no 

 soft, thin, or elongated pieces. 



The pea gravel, when tested by means of laboratory screens, shall Pea Grayel. 

 meet the following requirements : 



Per cent. 



Passing |-inch screen, not less than 95 



Retained on |-inch screen, not less than 85 



The coarse aggregate, when tested by means of laboratory screens. Coarse 

 shall meet the following requirements : Aggregate. 



Per cent. 



Passing 1-inch screen, not less than 95 



Total passing |-inch screen 25 to 75 



Retained on J-inch screen, not less than 85 



SAND. 



The sand for fine aggregate shall be composed of sound, durable stone General. 



particles, free from a coating of clay or loam. 



When tested by means of laboratory screens and sieves, the sand shall Grading. 



meet the following requirements : 



Per cent. 



Passing J-inch screen 100 



Total passing 40-mesh sieve , 30 to 70 



Retained on 200 mesh sieve, not less than ; 90 



MINERAL FILLER. 



The mineral filler shall consist of limestone dust, dolomite dust. Port- General. 

 land 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 Fineness. 

 meet the following requirements : 



Per cent. 



Passing 30 mesh sieve 100 



Total passing 200 mesh sieve, not less than 65 



Tests of the grading of the gravel, sand, and filler shall be made in Methods of 

 accordance with the following methods : Testing. 



Grading of Gravel, U. S. Department of Agriculture Bulletin 555, p. 32. 



Grading of Sand and Mineral Filler, U. S. Department of Agriculture 

 Bulletin 555, p. 33. 



This specification is intended to cover the mineral constituents 

 of a roughly proportioned bituminous concrete consisting of from 

 45 to 60 per cent gravel or coarse aggregate, from 30 to 45 per 

 cent sand or fine aggregate, from 3 to 5 per cent mineral filler, and 

 from 5 to 8 per cent bitumen. This mixture should preferably be 

 58688°— 18— Bull. 704 8 



