OFFICE OF PUBLIC ROADS. 791 



In the course of experimentation the discovery was made in the 

 testing laboratories of the Office of PubHc Roads that it was possible 

 to mingle mineral oils with the concrete while it was still wet and 

 before it was laid or molded in the forms. Tliis discovery has been 

 made the subject of a very systematic investigation. A very large 

 number of test pieces have been made containing varying quantities 

 of different brands and types of oils, and a very large amount of 

 useful information has been collected. The results of these sys- 

 tematic investigations will soon be published. In the mean time 

 the work is already being taken up in a practical way in actual 

 construction. Under the supervision of the Office, several road sur- 

 faces have been made of oil-cement concrete. One of these roads 

 is located in New Jersey and another in the District of Columbia. 

 In addition to this, a bridge surface has been constructed of this 

 material in New Jersey. After bein^ laid and in use for nearly a year, 

 these surfaces have given successful results. The use of oil-cement 

 concrete is, however, by no means confined to road-surface construc- 

 tion, for it can be used to replace ordinary cement concrete under 

 almost all conditions. Floors, cellars, foundation walls, tanks, silos, 

 manure pits, and similar constructions where strength, solidity, and 

 waterproof qualities require to be combined can be to-day built out 

 of oil-cement concrete. 



In the investigations varying amounts of oil have been added, but 

 the best results are obtained when the amount of oil used represents 

 from about 10 to 15 per cent of the weight of the cement used in 

 mixing the aggregate. The mixing presents no difiiculties whatso- 

 ever, either when the concrete is mixed by hand with shovels or 

 when a mechanical mixer of the revolving-barrel type is used. The 

 method of mixing oil-cement concrete does not difter materially from 

 that used in mixing ordinary concrete. The method followed is to 

 mingle the proper quantities of cement, sand, and water, and, as soon 

 as these have been given a preliminary mixing, a suitable quantity 

 of the oil is added, followed by the gravel or broken-stone aggre- 

 gate. The subsequent mixing presents no difficulties and takes very 

 little longer than in ordinary work. Oil-cement concrete has been 

 given a practical application recently in the construction of a series 

 of new vaults at the United States Treasury. In this case a one- 

 two-four mixture was used, that is to say, one part of cement, two of 

 sand, and four of clean gravel. The oil used is known as Standard Flux 

 55 Maltha. The quantity of oil was 10 per cent of the weight of the 

 cement used in the mixture. It is confidently believed that, in the 

 course of time, as soon as engineers have assured themselves of the 

 value of this form of construction, it will very largely replace the 

 ordinary methods of reinforced concrete construction. The great 

 advantages of oil-cement concrete lie in the fact that it is much more 

 dense, entirely waterproof, and develops an ultimate strength of 

 about the same order of magnitudes as concrete mixtures wliich do 

 not contain any oil. 



LIBRARY. 



The library of this Office has grown considerably in the past few 

 years and now contains an excellent collection of publications dealing 

 with road construction and allied subjects. It is the aim of the 

 library to secure copies of all recent publications on subjects con- 



