JOMa OF AGRmilAL RESEARCH 



Voiv. X Washington, D. C, August 13, 1917 No. 7 



TOUGHNESS OF BITUMINOUS AGGREGATES 



By Charles S. Reeve, Chemist, and Richard H. Lewis, Assistant Chemist, Office 

 of Public Roads and Rural Engineering, United States Department of Agriculture 



INTRODUCTION 



The following investigation was instituted as a result of certain obser- 

 vations on the part of one of the authors through an extended inspection 

 of a large mileage of bituminous-concrete roads in New England. The 

 mixes were largely of the one-size stone type, using crusher run of ap- 

 proximately the size that would pass a iX-inch screen and be retained 

 on a j4-mch. screen. The predominating rocks used were field stone of 

 granitic or gneissoid character. The exceptions were a few sections con- 

 structed with quartzite or trap rock. Coal-tar binders were used almost 

 exclusively in this work, and in most cases they were fluid products of 

 about the consistency commonly required for hot-surface applications. 



The careful inspection of a large mileage of roads constructed by the 

 mixing method with the materials above noted showed conclusively a 

 more pronounced and frequently quite rapid failure of sections in which 

 trap rock or quartzite was used than in those sections constructed with 

 native field stone. In fact, the difference in behavior was so marked 

 that one engineer ventured the observation that trap rock was not 

 adapted to bituminous construction. The excellent behavior of the tar 

 trap-rock sections constructed by the same method and exposed to 

 heavy traffic at Jamaica, N. Y.,^ offered positive evidence to the contrary, 

 although it is to be noted that a heavier grade of tar product was used 

 than had been the case in the New England work. There appeared, 

 however, to be no room for doubt that various rocks behaved differently 

 in combination with the same bitumen, and it was in an endeavor to 

 determine, if possible, what particular characteristic was responsible for 

 the difference in behavior that the experimental work described in this 

 paper was undertaken. 



EXPERIMENTAL DATA 



A number of large representative samples of various types of rock 

 were selected, including those which had been under observation in the 

 construction above referred to. The samples were passed through a 

 small jaw crusher and reduced to particles ranging in size from X ii^^h 



I PROGRESS REPORTS OF EXPERIMENTS IN DUST PREVENTION AND ROAD PRESERVATION, 1911. U. S. 



Dept. Agr. Off. Pub. Roads Circ. 98, 47 p. 191a. 



Journal of Agricultural Research, Vol. X, No. 7 



Washington, D. C. Aug. 13, 1917 



jf Key No. D— 13 



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