2 BULLETIN 347, U. S. DEPARTMENT OP AGRICULTURE. 



since that time in the actual routine of testing has shown the neces- 

 sity of strictly adhering to many apparently minor details the 

 importance of which was not formerly fully emphasized. Particular 

 stress has been laid upon these details, in order that others engaged 

 in, or about to engage in, this line of work may, with the least amount 

 of preliminary experimentation, obtain results of practical value. 



The first systematic attempts to determine the value of rock for 

 road-building purposes by means of laboratory tests were made in 

 France, where in 1878 a road-material laboratory was founded in the 

 French School of Bridges and Roads at Paris. Here the Deval abra- 

 sion test was adopted, and this test with slight modification has been 

 accepted as standard throughout the United States. The test is 

 named from its inventor and was first used in connection with con- 

 tract work in the city of Paris. Many valuable data were also col- 

 lected in this laboratory on the hardness and toughness of rock, and 

 tests for these properties were developed which were, in principle, 

 the same as those in use to-day. 



Outside of France very little work was done in road-material test- 

 ing in either Europe or America until 1893, when the Massachusetts 

 Highway Commission established a laboratory in the Lawrence 

 Scientific School of Harvard University, under the direction of Logan 

 Waller Page. The Deval abrasion test was adopted and a test to 

 determine the binding power of rock dust was developed by Mr. Page 

 in this laboratory. 



In December, 1900, the United States Government established a 

 laboratory in the Bureau of Chemistry of the Department of Agri- 

 culture, under the direction of Mr. Page. This laboratory became in 

 1905 a part of the Division of Tests of the newly organized Federal 

 Office of Public Roads. On July 1, 1915, during a general reorganiza- 

 tion, it was placed in the Division of Road Material Tests and Re- 

 search of the new Office of Public Roads and Rural Engineering. The 

 recent general interest in road improvement has also resulted in the 

 establishment of many laboratories in technical and scientific insti- 

 tutions both in this country and abroad, as well as in the various 

 State highway commissions. 



PHYSICAL PROPERTIES OF ROAD-BUILDING ROCK. 



The suitability of rock for use in highway construction is largely 

 determined in the laboratory by tests of certain physical properties 

 which have a direct bearing upon the behavior of the rock under 

 service conditions. In the case of rock intended for use in water- 

 bound macadam construction, experience has shown that the 

 qualities most essential to success are those of hardness, toughness, 

 and binding power. These properties may be briefly defined as 

 follows : 



