TESTS OF ROAD-BUILDING ROCK IN 1916. 

 Table IV. — General limitint/ test values for broken stone. 



23 





Traffic 1 



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 or over. 



7 or over. 

 13 or over. 



6 or over. 



8 or over. 



9 or over. 

 3 or over. 



10 to 17 



Water-bound macadam, plain or with dust 







palliative treatment. 











( 2 ) 





Moderate to heavy. . 

 /Light to moderate . . . 

 (Moderate to heavy . . 





( 2 ) 







Binder course for sheet asphalt or Topeka 

 type. 



( 2 ) 



Moderate to heavy . . 





Stone paving block 4 



Broken stone foundations 





do 



8 or over. 







1 





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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