RURAL ENGINEERING. 685 



pp. S80, SSI).— An extended series of tests in which five lots of 100 each of 6-in. 

 cubes, mixed in the proportions of 1 part cement, 2 parts sand, and 4 parts 

 blast furnace slag and passing the l^ln. sieve but retained on the li-in. sieve, 

 were crushed at periods of 28 days, 3 mouths, 6 months, 9 monWis, and 1 year, 

 respectively, is reported. 



The results Indicate that slag may be employed as an aggregate in competi- 

 tion with broken stone or gravel. " From the actual strength of the concrete 

 developed in these tests, its weight per cubic foot, the recognized solubility of 

 slag which permits it to act as a puzzolanic material, its alkaline nature which 

 is especially conducive to rust-proof in the case of reinforced concrete, and from 

 the relatively high combined percentages of silica, alumina, and iron, which 

 make for permanency of the resulting concrete, the conclusion Is that slag is 

 satisfactory for use as an aggregate in concrete." 



Oil-mixed Portland cement concrete, L. W. Page (17. S. Dept. Agr. Bui. 230 

 {1915), pp. 26, pis. 6, figs. 7).— This is a revision of Office of Public Roads 

 Bulletin 46 (E. S. R., 28, p. 85) and presents the re.sults of more recent labora- 

 tory and service tests of oil-mixed concrete. 



The conclusions so far reached are summarized as follows : " The admixture 

 of oil is not detrimental to the tensile strength of mortar composed of 1 part 

 cement and 3 parts sand when the oil added does not exceed 10 per cent of the 

 weight of the cement used. The compressive strength of mortar and of con- 

 crete suffers slightly with the addition of oil, although when not to exceed 10 

 per cent of oil is added the decrease in strength is not serious. Concrete mixed 

 with oil requires a period of time from 50 to 100 per cent longer to set hard 

 than does plain concrete, but the increase in strength is nearly as rapid in the 

 oil-mixed material as in the plain concrete. Concrete and mortar containing oil 

 admixtures are almost perfectly nonabsorbent of water and are therefore excel- 

 lent materials to use in damp-proof construction. The addition of oil, however, 

 does not appear to increase to any great extent the impermeability of concrete 

 subjected to heavy water pressure, and this method alone will probably not make 

 the concrete proof against the actual percolation of water through the 

 mass .... Laboratory tests show that oil-mixed concrete is just as tough and 

 stiff as plain concrete, and, furthermore, its elastic behavior within working 

 limits of stress is identical with that of plain concrete. The bond between con- 

 crete and plain-bar reinforcement is decreased by the use of oil in the concrete, 

 hut when deformed bars, wire mesh, or expanded metal is used there is no 

 apparent decrease in the bond." 



A series of experiments to determine what effect the addition of oil has in 

 retarding the action of alkali salts on the cement indicated that the action of a 

 10 per cent solution of sodium sulphate was materially retarded by the addi- 

 tion of 5 to 10 per cent of oil to a 1 : 3 mixture. 



Of 29 replies to letters inquiring as to the success or failure obtained by users 

 of oil-mixed concrete, only three were wholly unfavorable. 



Portland cement concrete pavements for country roads, C. H. Moorefield 

 and J. T. Voshfxl (U. S. Dept. Agr. Bui. 2J,9 {1915), pp. 34, pis. 11).— It is the 

 purpose of this bulletin to supply information on the subject of Portland 

 cement concrete pavements for the use of highway engineers and others in- 

 terested in the improvement of public roads. 



It is stated that the economic efficiency of concrete roads is undetermined 

 at present, but the indications are that this type of construction will prove 

 to be well suited for certain conditions. The principal advantages possessed 

 by concrete pavements are briefly stated as follows: "(1) As far as can be 

 judged, they are durable under ordinary suburban and rural traffic conditions. 

 , . . (2) They present a smooth, even surface, which offers very little resist- 



