RECEMENTATION. 1 1 



attempts to secure the briquette by various clamping devices were not 

 satisfactory. Finally the method was adopted of placing a drop of 

 thick shellac on the bottom of the test piece, which causes it to adhere 

 firmly to the bedplate. Careful attention to such details as these is 

 necessary in order to get satisfactory results from this test. 



The original method for molding the briquettes was worked out in 

 the laboratory of the Massachusetts Highway Commission and differs 

 somewhat from the method described above. In the earlier practice 

 the requisite amount of rock dust to make a briquette was weighed 

 out while dry, mixed with 3 to 4 cc of water, and the briquette imme- 

 diately molded from the wet dust. It is well known to practical road 

 builders that the binding power of many rocks increases under the 

 combined influence of water and traffic as time goes on. This ques- 

 tion has received a great deal of attention and investigation in this 

 laboratory and will be fully discussed later on. 



CEMENTATION AND BECEMENTATION. 



In the earlier practice of the laboratory it was the custom to make 

 a recementation test. The fragments of the briquettes from the 

 cementation test were ground, again mixed with a definite quantity of 

 water and immediately remolded into briquettes. This was done on 

 the theory that the rock dust on a road surface is continually being 

 cemented, broken up, and recemented under traffic. A very large 

 number of tests showed that the recementing values in by far. the 

 larger number of cases were smaller than the corresponding cement- 

 ing values. There were, however, a number of cases in which the 

 reverse took place. This is shown in the following table, in which the 

 cementing and recementing values of a number of rock species are 

 compared: 



TABLE I. Comparison of cementing and recementing values. 



These anomalous results called for a thorough investigation of the 

 whole question. As it is well known in clay working that the soaking 

 and kneading of a clay for protracted periods increases not only the 



