4 BULLETIN 704, U. S. DEPARTMENT OF AGRICULTURE. 
General. 
Physical 
Properties. 
Screenings. 
Top Course 
Stone. 
Bottom Course 
Stone. 
Methods of 
Testing. 
SPECIFICATION RW-1. 
Broken Stone for Water-bound 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 disinte- 
grated stone, dirt, or other objectionable matter. 
The stone shall meet the following requirement: 
Hrench coeficient of wear noless than sss pia eee 6 
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. 
PAS SUT aU Sra CES CLC CM oe a aR a A 100 
Total passmisy tin ChUs cr eenes ats a ae ean seey es ane ee eee Aras. 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. 
iPassine (2-1nchsereen, ‘not less: than 522928 =e ae ee es eee 95 
Totalipassinew:. inch Screen’ aaa eee ee ee 25 to 75 
Retained/on“l=ineh ‘screen, notiless) than] =e es eee 85 
That portion of the product of the crusher which when tested by means 
of laboratory screens will meet the following requirements: 
Per cent. 
Passiners-inchrScreen. snot, less eh =a. ee see ee ee eee 95 
AMoueUL jos Rabaver Era b aol al WGKerReYey ao a 25 to 75 
Retainedvon’2-1n ChySCreens: 1106 pleSSipctelo ean eee 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. 5d. 
2. 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 broken-stone road by the usual water-bound 
macadam methods. In certain instances the use of granite, gneiss, 
sandstone, or quartzite may ve allowed in the 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 ¢o- 
efficient of wear of 7.0 is to be considered here in the light of a 
minimum requirement under rather light traffic 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 properly 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. 
