12 BULLETIN 704, U. S. DEPAETMENT OF AGRICULTURE. 



SAND FOE SHEET-ASPHALT WEARING COURSE. 



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



free from a coating of clay or loam. 



Grading. 'Wlien tested by means of laboratory sieves the sand shall meet the 

 following requirements : 



Per cent. 



Passing 10-mesh sieve 100 



Total passing 10-mesh and retained on 40-mesh sieve 12 to 50 



Passing 10-mesh and retained on 20-mesh sieve 2 to 15 



Passing 20-mesh and retained on 30-mesh sieve 5 to 15 



Passing .30-mesh and retained on 40-mesh sieve 5 to 25 



Passing 40-mesh and retained on 50-mesh sieve 5 to 30 



Passing 50-mesh and retained on 80-mesh sieve 5 to 40 



Total passing 80-mesh and retained on 200-mesh sieve 20 to 40 



Passing 80-mesh and retained on 100-mesh sieve 6 to 20 



Passing 100-mesh and retained on 200-mesh sieve 10 to 25 



Passing 200-mesh sieve to 5 



MINERAL FILLER FOR SHBET-ASPHALT WEARING COURSE. 



General. 



Fineness. 



Methods of 

 Testing. 



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 



Tests of the physical properties of the rock and of the size, mechani- 

 cal analysis, or grading of broken stone, sand, and mineral filler shall be 

 made in accordance with the following methods : 



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



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



p. 32. 



3. Mechanical analysis or grading of sand and mineral filler, U. S. 



Department of Agriculture Bulletin 555, p. 33. 



This specification is intended to covei* the mineral constituents 

 and rough grading of tlie mineral aggregate of a binder course 

 and the sand and mineral filler for a sheet-asphalt wearing course. 

 The gradings are essentially those included in Specifications for 

 Shet.t Asphalt Paving adopted by the American Society of Munici- 

 pal Improvements in 1915. The aggregate for binder course will 

 carry from 4 to 7 per cent bitumen. It should be laid upon a con- 

 crete base so as to produce a thickness after compaction of about 

 11 inches. 



In order to secure the specified sand grading for the wearing 

 course it may be necessary to combine two or more sands in pre- 

 determined proportions. The surface mixture should be com- 

 posed of sand, mineral filler, and asphalt cement. It should carry 

 from 6 to 20 per cent filler and from 9* to 13^ per cent bitumen. 

 It should be laid upon the binder course so as to produce a com- 

 pacted wearing course li or 2 inches thick as desired. Mainte- 

 nance of the wearing course should consist only in patching with 

 sheet asphalt topping until it is necessary to rephice the entire 

 course. 



