OFFICE OF PUBLIC EOADS. 739 



PHYSICAL TESTS. 



The rocks tested included 42 samples of trap rock, 74 of limestone 

 and dolomite, 22 of sandstone, 11 of granite, 35 of gneiss, schist, 

 shale, and slate^ 18 of slag, 31 of sand, clay, and gravel, and 1,907 

 miscellaneous samples of a great variety of road-building materials, 

 exclusive of oils, tars, and other dust-preventives and road-pre- 

 servatives. These were received from a widely distributed area, 

 including 42 States and Territories, Porto Eico, Canada, and Ger- 

 many. The States sending the greatest number of samples were 

 Pennsylvania, 42; Virginia, 41; New York, 22; Illinois, 14; Ohio, 14; 

 and Maryland, 12. Laboratory investigations of slag for road- 

 building have been continued and information has been collected 

 regarding cement-slag mixtures and concretes. 



As in the past, instruction has been given in the testing laboratory 

 to student engineers and assistant highway engineers who have 

 become recently connected with the office. From this laboratory 

 course of instruction, the jfield engineer receives knowledge which 

 enables him to cooperate more intelligently with the laboratory in 

 road material investigations^ in addition to gaining a more intimate 

 acquaintance with the physical qualities of the materials which he 

 uses in construction. 



More equipment has been added to the laboratory for original 

 research work, including a compressometer of an improved electric 

 contact type, a strain gauge and a special micrometer for concrete 

 expansion and contraction measurements, designed and constructed 

 in the office. A large reinforced-concrete storage tank for concrete 

 specimens, and aditional cement testing equipment have likewise 

 been installed. 



Eesearch work in concrete has been carried on with increased 

 vigor, including investigations of oil-mixed concrete, principally 

 with reference to its road-building and water-proofing qualities, and 

 a study of the expansion and contraction of concrete while harden- 

 ing, a problem which is of much importance in connection with 

 concrete pavements. 



The results of these experiments have been published in the Pro- 

 ceedings of the American Society of Civil Engineers and in the 

 Engineering News of October 12, 1911. 



Research work is likewise being conducted with concrete water- 

 proofing materials. In addition, investigations are now under way 

 on road-building gravels and also on full-sized concrete-arch culverts, 

 such as are used under roads. It is anticipated that many valuable 

 data will be collected, which will be useful in the development of 

 more economical and better designs for this class of structure. 



OIL-MIXED CONCRETE. 



A very important discovery — that of oil-mixed concrete — was made 

 during the fiscal year 1910 in the progress of the development of a 

 resilient, dustless, nonabsorbent road material capable of withstand- 

 ing the severe shearing and raveling attacks of automobile traffic. 

 Enormous strides have been made in the use of Portland-cement con- 

 crete in the last decade. The quality, however, of this material has 

 not advanced in a corresponding degree. Although one of the most 



