8 BULLETIN 704, U. S. DEPARTMENT OF AGRICULTURE. 
of 2 inches snecified for the wearing course is on the basis of a 
course 23 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 asa 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. 
Broken Stone for One-size Stone Bituminous Concrete Wearing Course. 
Lone 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 
Physical free or as a coating on the stone. ; 
Properties. The stone shall meet the following requirements: 
NAKA oOKS MEMO Vere, ino Ness lnghine se ee sas 
Toughness; mot! TESs) >the arse ee ae a ae ee 8 
Chips: That portion of the product of the crusher, which, when tested by 
means of laboratory screens will meet the following requirements : 
Per cent. 
Rassitens-in Chi (SCreen sen Oita ES Sith ctr ee eee 95 
Retained on 34-inch screen, not less than_________» ______________ 85 
Bear cRale- That portion of the product of the crusher which, when tested by 
means of laboratory screens, will meet the following requirements : 
Per cent. 
JRC bee Doel Geren, MOE NESS Wein 3 95 
Motale passine, F-inielig=SGRe em sess eee eee eee ee aks ET es 25 to 75 
Retained on; 4-Inch> screen? not less, than-=3 2 see 85 
nes of 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 Agricuiture Bulletin 
3%87(5 0b Lie 
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- 
rials, covered with material conforming to Specification RS-2, 
