OFFICE OF PUBLIC EOADS AND RURAL ENGINEERING. 323 



During the fiscal year 28 new models were constructed for the 

 Panama-Pacific Exposition at San Francisco, among which were in- 

 cluded a model showing road relocation and a model showing road- 

 side treatment. In addition, 14 other new models were constructed 

 and old models were repaired as necessary. 



PUBLICATIONS. 



Four publications were issued, as follows: Department Bulletin 

 No. 136, " Highway Bonds ; " Report of the Director of the Office 

 of Public Eoads for the fiscal year 1914; Department Bulletin No. 

 220, "Eoad Models; " Circular No. 49 of the Office of the Secretary, 

 "Motor Vehicle Eegistrations and Revenues, 1914." Three other 

 manuscripts and two revisions of bulletins were prepared and in 

 press during this fiscal year, and will be issued shortly as Department 

 Bulletins, namely : " Vitrified Brick Pavements for Country Roads ; " 

 " Portland Cement Concrete Pavements for Country Roads ; " " Oil- 

 Mixed Portland Cement Concrete ; " " Progress Reports of Experi- 

 ments in Dust Prevention and Road Preservation, 1914 ; " " Construc- 

 tion and Maintenance of Roads and Bridges, from July 1, 1913, to 

 December 31, 1914." Manuscript of an article on State Road Manage- 

 ment for the 1914 Agricultural Yearbook was also prepared. 



INVESTIGATION OF ROAD MATERIALS. 



During the year a total of 1,049 samples were received by the 

 physical and chemical testing laboratories to be examined to deter- 

 mine their suitability for road-building purposes. This is an in- 

 crease of nearly 15 per cent over the number received during the 

 preceding year. 



PHYSICAL TESTS. 



The physical testing laboratory, under the supervision of E. B. 

 McCormick, mechanical engineer, received 630 samples, classified as 

 follows : Gravel, 153 ; limestone, 86 ; dolomite, 48 ; granite, 37 ; sand- 

 stone, 31; cement, 22; gneiss, 20; diabase, 19; sand, 18; concrete, 18; 

 clay, 15; schist, 11; miscellaneous, including samples of marl, shell, 

 slag, etc., 77 ; samples on hand and unclassified July 1, 1915, 75. 



States from which the largest number of samples were received 

 are as follows: Texas, 66; Virginia, 62; Ohio, 28; Tennessee, 27; 

 Indiana, 26 ; Iowa, 23 ; Illinois, 22 ; Maryland, 20 ; West Virginia, 19. 



Research into the road-building qualities of gravel was carried on 

 throughout the year. An investigation of the present cementing- 

 value test, for the purpose of determining the uniformity of results 

 obtainable, was also carried out. The effect of frost on the strength 

 of rock and cement mortar was studied by means of the refrigeration 

 machine installed in the laboratory. 



Concrete investigations, including the effect of vibration on the 

 strength and time of setting of cement mortars and concrete, and a 

 continuation of the concrete bridge-slab experiments, were carried on. 

 Observations of the changes in length occurring in concrete roads 

 under different weather conditions have been continued. Consider- 

 able work was also done on the standardization of tests for concrete 



