TESTS OF ROAD-BUILDING ROCK IN 1916. 23 
Table IV. — General limiting test values for broken stone. 
Traffic, i 
Limiting values. 
Type of construction. 
French 
coefficient 
of wear. 
Toughness. Hardness. 
[Light 
5 to 8 
9 to 15 
16 or over. 
5 or over. 
7 or over. 
7 or over. 
10 or over. 
7 or over. 
( 3 ) 
( 3 ) 
3 or over. 
5 to 9 
10 to 18 
19 or over. 
5 or over. 
10 to 17 
Water-bound macadam, plain or with dust 
palliative treatment. 
[Heavy 
Macadam with bituminous carpet 
Bituminous macadam with seal coat 
Light to moderate. .. 
Moderate to heavy. . 
("Light to moderate . . . 
(Moderate to heavy . . 
Any 
( 2 ) 
7 or over. 
13 or over. 
( 2 ) 
Binder course for sheet asphalt or Topeka 
type. 
( 2 ) 
Moderate to heavy . . 
8 or over. 
9 or over. 
Stone paving block 4 
do 
i 
1 Light traffic is assumed as less than 100 vehicles per day, moderate traffic between 100 and 250 vehicles, 
and heavy traffic over 250 vehicles per day. 
2 Numerous tests have shown that limits for hardness are unnecessary if the material possesses the re- 
quired French coefficient of wear and toughness. 
3 Limits for French coefficient of wear are not at present considered necessary for this type of construction. 
4 Crushing strength, 20,000 pounds or over per square inch is sometimes required. 
Cementing values should show over 25 in all cases if material is to be 
used in water-bound macadam construction. 
In general, granites, gneisses, schists, sandstones, and quartzites 
should not be used in the wearing course of water-bound macadam 
roads. Shales and slates never should be used in this connection; 
therefore cementing value tests have been discontinued on these 
materials. 
For further details and explanation of results in this table and also 
for tests on all materials to January 1, 1916, see U. S. Department of 
Agriculture Bulletin No. 370. 
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