REPORT OF THE SECRETARY. 149 



economy and of safet}'. One of the peculiar difficulties encountered 

 by the local communities with regard to bridges and culverts is that 

 the great majority of these structures are comparatively small, so 

 that those in responsible charge do not feel warranted in incurring 

 the expense incident to the employment of skilled engineering assist- 

 ance. Requests are continually being received for information 

 concerninir the use of concrete and other materials for bridijes and cvA- 

 verts. Such information is being collected and disseminated. One 

 bulletin dealing with this subject has already been published and 

 others are in course of preparation. The published information is 

 supplemented by personal inspection, advice, plans, and superin- 

 tendence by the engineers of the office when request is made through 

 the proper local authorities. 



TESTING or ROAD MATERIALS. 



In the routine testing and examination of road materials great 

 progress has been made along established lines. The total number 

 of samples tested during the year was 685, which were received from 

 a widely distributed area, including 42 States and Territories, Porto 

 Rico, Canada, and Germany. During the year 324 samples, mostly 

 bitumens, were received for examination in the chemical laboratories. 

 This is nearly twice the number examined during the previous year, 

 and more than four times the number examined in 1909. Much 

 valuable work has also been done in standardizing methods of test- 

 ing and examining road binders and other materials. It has been 

 found that the addition of a small proportion of cement to blast- 

 furnace slag screenings increases the cementing properties very 

 greatly. These investigations will be continued both in laboratory 

 studies and in service experiments in the field during the coming year. 

 Research work in concrete has been carried on with increased vigor. 

 These investigations include a study of oil-mixed cement concrete, 

 principally with reference to its road-building and water-proofing 

 properties, and also a study of the expansion and contraction of con- 

 crete while hardening, a subject of much importance in connection 

 with concrete pavements. 



INVESTIGATION OF ROAD BINDERS AND DUST PRE\T:NTIVES. 



Investigation of the problems of dust prevention and road pres- 

 ervation has occupied much attention during the year. Commend- 

 able progress has been made in the several lines of work. Demand 

 for specifications covering the various types of bituminous binders 

 and bituminous road construction is continually increasing. During 

 the year 81 sets of specifications were furnished, on request, to 

 officials in 20 different States, and also to the Reclamation Service, 

 the Navy Department, and the War Department. 



