UNITED STATES DEPARTMENT OF AGRICULTURE 



SV9^rWu 



1 BULLETIN No. 348 



Contribution from the Office of Public Roads and Rural 

 Engineering, LOGAN WALLER PAGE, Director 





Washington, D. C. 



PROFESSIONAL PAPER 



April 4, 1916 



RELATION OF MINERAL COMPOSITION AND ROCK STRUCTURE 

 TO THE PHYSICAL PROPERTIES OF ROAD MATERIALS. 



By E. C. E. Lord, Petrographer. 



CONTENTS. 



Introduction 



Examination and classification of rocks for 

 road making 



Mineral composition of rocks for road mak- 

 ing 



Physical properties of road materials 



Page. 

 1 



Page. 



General relation between the physical prop- 

 erties of rocks and their mineral composi- 

 tion and structure 11 



Effect of secondary minerals on the physical 

 properties of rocks for road building 13 



Summary and conclusion 24 



INTRODUCTION. 



The importance of selecting proper materials for the construction 

 of macadam roads has become generally recognized and has led to a 

 careful study in this office of a large number of rocks in order to 

 properly determine their mineral composition and road-making prop- 

 erties. The earlier results of these investigations, which were pub- 

 lished in 1911/ have demonstrated that certain physical properties 

 are in a general way characteristic of definite rock types and may be 

 attributed to the peculiar arrangement and composition of the rock- 

 forming constituents. With a largely increased number of samples 

 available for examination it has been found possible to correlate these 

 relations more exactly, and in the present publication the results 

 obtained will be presented with special reference to the effect of 

 secondary minerals on the physical properties of rocks for road 

 building. 



In considering these results it should be noted that owing to the 

 complexity of the subject and of the possible effect of many variables, 

 it has not been possible to develop definite laws. The discussion of 

 the effect of secondary minerals has therefore been based necessarily 



1 Examination and Classification of Rocks for Road Building, TJ. S. Office of Public Roads Bui. 37. 

 17715°— Bull. 348—16 1 



