492 ANNUAL EEPOETS OF DEPARTMENT OF AGRICULTURE. 



a view to their prevention. This is a most important subject, in view 

 of the large mileage of gravel roads already built. In connection with 

 this work a laboratory study of gravel is being made. 



Investigations of the warping and movement of road slabs as a 

 result of temperature changes, frost, moisture, and other natural 

 causes have been carried on at Arlington. 



Two bridge investigations have been instituted, one consisting 

 of the measurement of impact stresses and the other aiming to throw 

 light on the design of skew arches. A special photographic strain 

 gauge has been developed which permits of the very accurate deter- 

 mination of impact stresses. 



A field investigation of various types of culvert pipe in the Southern 

 States has been completed. 



RESEARCHES IN CONNECTION WITH NONBITUMINOUS MATERIALS. 



The following researches have been conducted in connection with 

 the use and characteristics of nonbituminous materials: A study of 

 the effect of alkali in mixing water on the strength of cement mortar; 

 a method of treating concrete drain tile with water-gas tar has been 

 developed which seems to greatly retard the destruction of this kind 

 of tile by alkalis. Analyses were made of 160 concrete sands for the 

 purpose of determining to what extent the color test for organic 

 content is dependable. An impact test was developed for the purpose 

 of determining the quality of gravel aggregates, and an investigation 

 was carried on in cooperation with the American Society for Testing: 

 Materials with the object of standardizing a compression test for 

 rock. 



In connection with the accelerated wear test which is to be con- 

 ducted at Arlington a series of abrasion tests were made on samples 

 of crushed stone, gravel; sand, slag, chats, etc., from various parts 

 of the United States. These aggregates, which have widely varying 

 qualities, are to be used in the construction of the experimental con- 

 crete road sections, and by correlating the results of the two series, 

 of experiments it is believed that it will be possible to establish a 

 relation between the quality of aggregates and the wear of the 

 pavement. 



RESEARCH IN CONNECTION WITH BITUMINOUS MATERIALS. 



Investigational work on bituminous materials has been con- 

 .centrated upon bituminous mixtures such as are used in the con- 

 struction of bituminous concrete and sheet-asphalt pavements. A 

 number of projects are under way which will lead to a better 

 knowledge of the essential characteristics of such mixtures and 

 of suitable methods for testing their qualities. 



To supplement the special tests of bitummous concrete pavements 

 which will be made at Arlington to determine the cause of wavy 

 surfaces, a study of asphalt pavements has been instituted m five 

 important cities in which different climatic conditions prevail. 

 This study will be conducted in cooperation with the street depart- 

 ments of 'the cities and the Asphalt Association. It will involve a 

 comprehensive series of tests of a large number of samples taken 

 from typical streets. The testing, which is now well under v/ay, 



