BULLETIX 704, U. S. DEPARTMENT OF AGRICULTURE. 



SPECIFICATION RW-1. 



General. 



rhyslcal 

 Properties. 



Screenings. 



Top Course 

 Stone. 



Bottom Course 

 Stone. 



Methods of 

 Testing. 



Broken Stone for Water-Tjound Macadam. 



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

 granite, gneiss, sandstone, quartzite, schist, shale, and slate, of uniform 

 quality throughout, free from thin or elongated pieces, soft or disiute- 

 grated stone, dirt, or other objectionable matter. 

 The stone shall meet the following requirement : 



French coefficient of wear, not less than 7 



That portion of the product of the crusher, including the dust of frac- 

 ture, which when tested by means of laboratory screens will meet the 

 following requirements : 



Per cent. 



Passing 1-inch screen 100 



Total passing J-inch screen 40 to 80 



That portion of the product of the crusher which when tested by means 

 of laboratory screens will meet the following requirements : 



Per cent. 



Passing 2-inch screen, not less than 95 



Total passing IJ-ineh screen 25 to 75 



Retained on 1-inch screen, not less than 85 



That portion of the product of the crusher which when tested by means 

 of laboratory screens will meet the following requirements : 



Per cent. 



Passing 3-inch screen, not less than 95 



Total passing 2J-inch screen 25 to 75 



Retained on 2-inch screen, not less than 85 



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 Agriculture Bulletin 



347, p. 5. 



2. Size, U. S, Department of Agriculture Bulletin 555, p. 82. 



This specification is intended to cover stone to be used in the 

 construction of a broken-stone road by the usual water-bound 

 macadam methods. In certain instances the use of granite, gneiss, 

 sandstone, or quartzite may be allowed in tlie bottom course, pro- 

 vided the material otherwise meets the specification. These types 

 would be excluded from the wearing course, owing to lack of bind- 

 ing qualities found in materials of this nature. The French co- 

 efficient of wear of 7.0 is to be considered here in the light of a 

 minimum requirement under rather light traflic conditions, unless 

 the road is to be maintained with a bituminous wearing mat or 

 carpet. The exact value to be inserted should be governed by the 

 character of available material and estimated traffic conditions. 

 For an ordinary water-bound road subjected to moderate traffic, a 

 coefficient of from 9 to 15 would be more satisfactory, while for 

 heavy traffic a value as high as 16.0 might be required. A coeffi- 

 cient of wear of not less than 7.0 is satisfactory when the road 

 surface is to be maintained with a bituminous material. 



It is estimated that for an average rock a bottom course 5 inches 

 and a wearing course 3 inches in thickness, before consolidation, 

 will utilize practically the entire product of an ordinary portable 

 crushing outfit and provide sufficient screenings to pi'operly bind 

 the surface, with a slight excess of screenings in the case of the 

 softer grades of rock, which may be used if desired in filling the 

 bottom course. 



