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CEMENTING POWER OF ROAD MATERIALS. 



It is the intention in this bulletin to give as concise a description as 

 possible of the investigation and results of tests of the important 

 property of road materials known as cementing power. In the course 

 of many years' investigation of this and allied problems a vast amount 

 of data has been accumulated, but the effort has been made at this time 

 to select only such as are necessar} 7 for the presentation and discussion 

 of the subject. 



CEMENTATION TEST." 



The binding or cementing power of rock dust is such an important 

 element in road building that much time has been spent in the endeavor 



FIG. 1. Ball mill. 



to devise a suitable test for determining the degree to which the vari- 

 ous rocks and gravels possess this property. Many tests have been 

 tried, but as yet only an impact test, carried on in a uniform manner 

 as described below, has given satisfactory results. 



One kilogram of the rock to be tested is broken sufficiently small to 

 pass a 6 mm, but not a 1 mm mesh screen. It is then placed in a 

 ball mill and ground for two and a half hours. This ball mill (fig. 1) 

 contains two chilled-steel balls, which weigh 25 pounds each, and is 



"The description of this test and the machines used is partly abstracted from Bui. 

 No. 79, Bureau of Chemistry. 



