740 ANNUAL, REPORTS OF DEPARTMENT OF AGRICULTURE. 



universally used structural materials, because of its many good 

 qualities, faults are apparent in its porosity and absorbent qualities 

 and in its tendency to develop cracks, due not only to temperature 

 changes, but to shrinkage while drying out in the air. 



Yearly the use of concrete is increasing in road construction, in 

 reinforced-concrete buildings, in sidewalks, basement floors, tanks, 

 silos, and numerous other structures about the farm, and without 

 doubt the curing of some of its present-day ills will render its useful- 

 ness more universal and vastly more efficient. It has been demon- 

 strated through laboratory and service tests conducted by the office 

 that some of the faults of plain concrete as ordinarily made may be 

 eliminated at a very low extra expense, by the incorporation of a non- 

 volatile mineral oil with the other materials in the mixture. 



In October, 1909, it was discovered that a considerable quantity of 

 oil could be combined with wet Portland-cement paste by a very 

 simple mixing process, and, furthermore, that there was no separation 

 of the oil from the paste after setting. The importance of this fact 

 was recognized, and immediately investigations were begun on oil- 

 mixed Portland-cement mortars and concretes, and during the present 

 fiscal year a large series of laboratory tests was conducted, using a 

 number of different types of oils and tar. In these experiments the 

 various physical properties of oil-mixed mortars and concrete were 

 investigated, including tensile strength, time of setting, crushing 

 strength, toughness, elasticity, absorption, permeability, and bond to 

 steel reinforcement. An enormous number of test specimens were 

 molded for these experiments, requiring the construction of a large 

 reinforced-concrete storage tank, built as an additional test of oil- 

 mixed concrete. A 1:2:4 mixture was used, containing 10 per cent 

 of oil based on the weight of cement. This tank is absolutely water- 

 tight. Laboratory tests show that, in general, oil has the following 

 effects on mortars or concrete mixtures: Tensile strength, not de- 

 creased; time of setting is lengthened; crushing strength, somewhat 

 decreased; toughness, not decreased; elasticity, not different from 

 ordinary concrete; absorption and porosity, greatly decreased; and 

 bond, slightly decreased. 



These tests show the advantage of oil-mixed concrete in structures 

 w^here a very inexpensive damp-proofing is desired, such as in pave- 

 ments, basement floors and walls, shallow tanks, concrete building 

 blocks, concrete roofs, etc. The indications of the usefulness of the 

 material shown in the laboratory are now being borne out in service 

 tests of basement floors, tanks, roofs, roads, bridge surfaces, etc. 



The best method of preparing oil-mixed concrete is to mix 

 together dry the required quantities of cement and sand until of 

 uniform color, then to add water and mix to a mortar of the desired 

 consistency. The required quantity of oil is then added to this 

 mortar and mixed until it entirely disappears. The oil-mortar thus 

 formed is then added to the previously moistened coarse aggregate 

 and the mass is turned until thoroughly mixed. Ten per cent of oil 

 based on the weight of cement in the mixture is all that is required 

 to produce a concrete with very small water absorption and 5 per 

 cent of oil is nearly as efficient. Roughly speaking, a mixture con- 

 taining 5 per cent of oil will require 5 quarts (about one-half bucket) 

 for every two bags of cement. In using a machine, experience has 

 shown that oil-mixed concrete may be mixed most expeditiously by 



