OFFICE OF PUBLIC ROADS AND RURAL ENGINEERING. 373 



designed and constructed. A paper also was presented before the 

 American Concrete Institute upon " Friction Tests of Concrete on 

 Various Supporting Mediums." These tests were made upon broken 

 stone, gravel, sand clay, clay, and soil subgrades. General test limits 

 for the physical i)r()perties of broken stone and gravel for various 

 types of road construction were adopted as a means of indicating the 

 value of samples examined and reported u^Don by the physical 

 laboratory. 



Investigations were continued on the following subjects: The 

 relative etfect of mortar and sand cushions for brick pavements; the 

 effect of freezing and thawing upon argillaceous materials. Plans 

 have been made for a detailed survey of quarry conditions in the 

 United States for the purpose of securing information upon quarry 

 practice as related to road building and of standardizing commercial 

 sizes of broken stone to be used for that purpose. 



STANDARDIZATION OF METHODS OF TESTING BITUMINOUS ROAD MATERIALS. 



A paper upon "A Xew Consistency Tester for Viscous Liquid Bitu- 

 minous Materials" was presented before the American Society for 

 Testing Materials. This paper describes an apparatus devised by 

 the office for accurately determining the consistency at normal tem- 

 perature of road oils and tars used in the hot surface treatment of 

 macadam and gravel roads. 



Investigations were continued upon the standardization of a 

 method of counting ultra microscopic particles in bituminous mate- 

 rials and the effect of controllable variables upon the float and melt- 

 ing-point tests. Cooperative work will be continued with the 

 American Society for Testing Materials in connection with a number 

 of proposed standard tests for bituminous road materials. 



STANDARDIZATION OF METHODS OF TESTING NONBITUMINOUS ROAD MATERIALS. 



A paper upon the "Effect of Controllable Variables upon the 

 Toughness Test" was presented before the American Society for 

 Testing Materials. As a result of cooperation with committee D-4 of 

 this society a new standard toughness test and a standard method of 

 determining the specific gravity of coarse aggregates was recom- 

 mended for adoption. The office also cooperated with the Bureau 

 of Standards and representatives of technical societies and various 

 manufacturing industries in the development of a standard scale for 

 laboratory sieves. 



Investigations have been continued and are now in progress upon 

 the following subjects: Improvement of the standard abrasion test 

 for rock; the standardization of an abrasion test for gravel : a method 

 of determining clay in aggregates; effect of controllable variables 

 upon the hardness test. 



CONCRETE INVESTIGATIONS. 



The following papers were prepared for department publication 

 or presentation before technical societies : " The Expansion and Con- 

 traction of Concrete," Department Bulletin ; " Effect of Grading on 

 Fine Aggregates for Concrete," Journal of Agricultural Research; 

 " Tests of a Large-sized Eeinforced Concrete Slab Subjected to Eccen- 



