Aug. 13. I9I7 Toughness of Bituminous Aggregates 329 



CONCLUSIONS 



From the foregoing investigation and data the following conclusions 

 may be drawn : 



(i ) The toughness of bituminous aggregates in which a given bituminous 

 material is used will not be the same for every type of rock. 



(2) Tests of laboratory specimens can be directly correlated with 

 results in service. 



(3) The difference in behavior of the various rock types can not be 

 directly attributed to any of the routine physical test values of the rock, 

 but appears to be due largely to differences in the surface character of the 

 rock particles. 



(4) While relatively soft or fluid bitumens may yield satisfactory 

 results in bituminous concrete with some types of rock, their use with 

 other types will lead to failure of the road surface. 



(5) The impact or toughness test of bituminous aggregates offers 

 possibilities as a means of determining in advance the relative behavior 

 in service of bituminous concretes. While the authors at this time have 

 no definite recommendations to offer with regard to their last conclusion, 

 it may be stated that further experiments will be made with that end in 

 view. 



