51() ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



Tlie distribution of this material and eriiiipnKmt will bo treated 

 at a later dat'* in a special ropor", whicli will inoliido tables shewing: 

 the amount of the several classes of material received and the 

 amount allo:,ted to each of the Stat3s. 



ROAD MATERIAL TESTS AND RESEARCH. 



Duriniz; the past (iscal year the work of this division has proceeded 

 vigorously, and although the routine testing has greatly increased in 

 scope, particular emphasis has been placed on the development of 

 the research work of the division. The vast expenditures of money 

 for road construction, when taken into consideration with the rapid 

 destruction of many road surfaces under heavy traffic, have rendered 

 it necessar}^ to institute a thorough investigation into the conditions 

 whicli make for such rapid destruction and to discover, if possible, 

 a means whereby designs of road surfaces may be provided to ade- 

 quately take care of heavy traffic. The plan of research outlined in 

 November of the preceding fiscal year working toward the more 

 adequate design of roads was followed and increased in scope and a 

 number of very enlightening facts have been developed during the 

 year. 



It was found, for example, in one series of tests with a loaded o-ton 

 truck traveling at 15 miles per hour and striking a surface depression 

 only one-quarter of an inch in depth that the rear wheels d.^livered 

 a blow to the read equivalent to lour times the static load. Carry- 

 ing the research a step farther it has been found that the intensity of 

 the blow elelivered is enormously reelucod by the use of pneumatic 

 instead of solid rubber tires. 



The investigations which have for their purpose the improvement 

 of methods of road surface design may be classifieel under the follow- 

 ing main heads : 



1. An investigation of subgraeles and elrainage. 



2. Determination of the impact of motor trucks on road surfaces, 



3. Investigation of the effect of impact on different types of road 

 surfaces. 



4. The relative w^earing qualities of different types of road surfaces. 

 Three of these investigations were started during the previous 



fiscal yeai', and the investigation of subgrades during the early part 

 of this fiscal year. Considerable headway has been made on all of 

 them. Two papers appeared in Public lloads giving the results of 

 the impact tests anel one paper describing the general character of 

 the entire investigation. One series of 49 roael surfaces has been 

 tested under the same kind of traffic and a paper on this subject 

 will appear shortly. ' In addition, the impact tests for determining 

 the relative load-carrjdng capacity of different surfaces are now about 

 half completed and a paper will likewise be published on this investi- 

 gation in a short time. 



CONCRETE INVESTIGATIONS. 



A series of tests was conducted to determine the crushing strength 

 of concrete as affected by the addition of hydrate of lime and to 

 determine the effect of mixing the concrete at a central mixing plant 

 and hauling it before elepositing at the work. 



