BUREAU OF PUBLIC ROADS. 385 



RESEARCH ON DUST PREVENTIVES AND ROAD BINDERS. 



As a result of research and experimental work as well as observa- 

 tion of the work of highway engineers throughout the country a 

 set of typical specifications for bituminous materials for various 

 types of roads and methods of use was prepared and sent to all 

 manufacturers who were thought to be interested, with the request 

 that they review the specifications and suggest changes if they 

 thought desirable, giving their reasons for such changes. Upon 

 receipt of all the information that could be secured, these specifi- 

 cations were redrafted and published as Department Bulletin 691, 

 under the title, "Typical Specifications for Bituminous Road Mate- 

 rials." This bulletin contains 30 specifications for petroleum, asphalt, 

 and tar products, with descriptions of the general methods of use for 

 which the materials are suitable, methods of testing the materials 

 for conformity with the specifications, and directions for sampling. 



An investigation of the relation of the consistency of road oils at 

 normal temperature to the so-called asphalt content test has been 

 completed. 



The following subjects are under investigation: The effect of vari- 

 ations in refining methods upon the characteristics of road oils and 

 asphalt produced from crude petroleum ; the thickness of bituminous 

 films upon different types of mineral aggregates ; the physical prop- 

 erties of coarse bituminous aggregates ; the effect of colloids on bitu- 

 minous materials. 



EXPERIMENTAL BITUMINOUS ROAD CONSTRUCTION AND MAINTENANCE. 



As in 1917, supervision and inspection of experimental bituminous 

 roads has been largely confined to the vicinity of Washington, al- 

 though inspections oi experimental surface treatments of gravel 

 roads were made in Texas and inspections of asphalt earth roads 

 were made in Missouri, Pennsylvania, New Jersey, and Connecticut. 



In all of the experimental work of the year, which included the 

 maintenance of roads constructed in previous years, this division co- 

 operated wdth the engineering division. A total of 40 inspections 

 was made. 



NONBITUMINOUS ROAD MATERIAL INVESTIGATIONS. 



During the year an exhaustive investigation of commercial quarry 

 practice in the production of crushed stone for road-bui'lding pur- 

 poses was begun. A special study was made of such practices in the 

 New England and Middle Atlantic States. A progress report of 

 these investigations was published under the title, " The Commercial 

 Sizes of Broken Stone Aggregate," in the June number of Public 

 Roads. A report was also prepared on small scale production of 

 crushed stone for public roads, dealing in an elementary manner 

 with the selection of quarry sites and the installation and operation 

 of suitable equipment. It is felt that such information is of great 

 value in furthering the use of local materials, which is particularly 

 desirable under present war conditions. A paper upon " Saving Fuel 

 in Highway Work " was also published in the May number of Pub- 

 lic Roads. 



