BUREAU OF PUBLIC ROADS. 493 



is designed to determine the characteristics of sheet-asphalt mixtures 

 that render them susceptible to the formation of waves. • 



In addition, a laboratory study of bituminous mixtures is in 

 progress to study methods of testing and determine essential qualities 

 of such mixtures as are used in highway construction. 



A number of investigations on oils, asphalts, and tars have been 

 carried out, particularly as to the methods of making the fixed- 

 carbon tests, the results of the volatilization test as applied to road 

 oils by two methods extensively used, and the consistency of refined 

 tars as determined by means of the softening point and float test. 

 The results of these investigations have been used in compiling 

 specifications for suitable bituminous road materials. 



A number of investigations looking to the standardization of 

 various tests for the quality of bituminous materials have been 

 made generally in cooperation with the American Society for Testing 

 Materials and the American Association of State Highway Officials. 

 A detailed study of the viscosity test has been undertaken and partially 

 completed, and the method of conducting the float test has been 

 standardized. Further work has been carried out in connection 

 with the distillation test for bituminous road materials. The com- 

 mittee on tests of the American Association of State Highway Officials 

 has held a number of meetings in various sections of the country at 

 which the bureau has been represented, and a great deal of progress 

 has been made in standardizing methods of testing to be applied to 

 materials used in Federal-aid road construction. 



FEDERAL-AID TESTING. 



One of the important functions of the division of tests is the 

 testing of materials used in Federal-aid road constructioji. The 

 routine testing of such materials is performed in a large number of 

 State highway laboratories and commercial laboratories throughout 

 the coimtry. This is necessary in order that the work may be done 

 expeditiously. It is higlily important that such testing he performed 

 in a standard manner and with skilled and careful operators. The 

 division of tests, by the use of check samples and by personal visits 

 to the various laboratories, aids in the establishment of standard 

 methods of testing and gives information on the correct methods to 

 he used. During the fiscal year 1,160 samples of materials used in 

 Federal-aid construction were received for testing, and personal 

 visits were made to 37 road-materials laboratories performing tests 

 on Federal-aid materials. 



INVESTIGATIONS IN COOPERATION WITH OTHER AGENCIES. 



In connection with its research program, the bureau has established 

 cooperative relations with other institutions, which give it the 

 benefit of increased personnel and testing facilities at a compara- 

 tively low cost, and %vhich will reduce the time necessary to complete 

 the work. Under the cooperative arrangements the cooperating 

 agency pays for approximately one-half of the cost of the investiga- 

 tion. During the past year such cooperative investigations have been 

 conducted by Purdue University, Iowa State College, University of 

 Maryland, University of Texas, Kansas Agricultural College, Mas- 



