REPORT OP THE SECRETARY. 209 



Much has been accomplished in the development of the physical 

 tests of rock for road building, and the methods here adopted are 

 now practically standard throughout the United States. 



Research work in concrete has been productive of promising re- 

 sults. The properties of oil-mixed Portland cement concrete have 

 been investigated, and indicate this material to be one of merit for 

 damp-proofing purposes. A public patent has been granted for this 

 material, so that any one may now use it without the payment of 

 royalties. Measurements of the expansion and contraction of con- 

 crete while hardening, which are of value to concrete engineers, have 

 aroused considerable interest and serve to explain certain phenomena 

 in connection with concrete construction. 



Experiments have been conducted to determine the efficiency of 

 oils, tars, asphalt, and other preparations used for the purpose of 

 preventing dust and preserving macadam roads under modern traffic 

 conditions. Laboratory experiments have been accompanied by serv- 

 ice tests and experiments in the field. The office has also conducted 

 investigations to determine the feasibility of building sand-clay and 

 burnt-clay roads in the Southern States and in the Mississippi Valley. 

 Such construction has been found to be practicable for certain regions 

 where materials are available and climatic conditions favorable. 



Successful efforts are constantly made to bring about a more gen- 

 eral use of the split-log drag in the maintenance of earth and gravel 

 roads. 



MODELS OF TYPES OF ROADS. 



In order to better demonstrate the fundamental principles of road 

 construction, the office has built a number of models of various 

 standard types of roads and bridges and of road-building equipment, 

 including road machines, rollers, and crushers. A set of models was 

 first exhibited at the Alaska- Yukon Exposition. Since that exposi- 

 tion closed, similar exhibits have been shown in many parts of the 

 United States through the medium of expositions and by means of 

 exhibit trains operated by various railroad companies. The cost of 

 making such demonstrations has been paid by the expositions or by 

 the railroad companies interested. Lecturers and demon?^trators from 

 the office have accompanied exhibits and made them to a large degree 

 schools in road building. 



TRAINING HIGHWAY ENGINEERS. 



Realizing the need for trained highway engineers, the office in- 

 augurated a plan in the year 1905 whereby a number of graduates 

 in engineering are appointed each year from engineering schools 

 and colleges after competitive examinations. These men are given 



70481°— AGB 1912 14 



