RURAL ENGINEERING. 687 



Supplementary reports are also given of experiments made at Washington, 

 D. C, on surface treatment by tar preparation and oils; at Chevy Chase, Md., on 

 bituminous construction, surface treatment, and the use of refined semiasphaltic 

 oil; at Jamaica, N. Y., on the use of oil-cement concrete, oil asphalt, tar, and 

 fluxed native asphalt ; at New York, N. Y., and Ridgewood, N. J., on oil-cement 

 conci'ete; at Boise, Idaho, on oil-gravel macadam; at Ames, Iowa, on oil- 

 asphalt gravel; at Knoxville, Tenn., on tar and oil preparations; at Youngs- 

 town, Ohio, on slag, slag and lime, slag and waste sulphite liquor preparation, 

 and slag and tar; at Newton, Mass., on asphaltic preparations, tar preparations, 

 residual oil, and molasses-oil-lime ; at Cardeu City, Dodge City, Bucklin, and 

 Ford, Kans., on sand clay; at Independence, Kans., on oil-asphalt earth road; 

 and at Bowling Green, Ky., on Kentucky rock asphalt. 



Standard abrasion test for gravel employed by the Ohio State Highway 

 Department, A. S. Rea (Good Roads, n. ser., 7 (1914), Na. 23, pp. 315, 316, 

 fig. 1). — In an attempt to obtain a satisfactory test for gravel which would 

 give a measure of its resistance to wear when subjected to traffic conditions, 

 the standard abrasion test for stone was modified, using the Deval type of abra- 

 sion machine and 6 cast-iron spheres such us are used in the standard paving- 

 brick i-attler test per cylinder for an abrasive charge. The gravel was screened 

 ihrough screens having 2-in., 1-in., and i-in. circular openings, and the sizes 

 used for the tests were equally divided between those passing the 2-iu. and 

 retained on the 1-in. screen, and those i)assing the 1-in. and retained on the 

 ^-in. screen. The duration of the test and the rate of rotation wex'e 10,000 

 I'evolutions at the rate of from 30 to 3.3 revolutions per minute. 



A series of tests made to comiiare the results obtained with those from the 

 .standard stone test show the advantage of this test, aside from the considera- 

 tion of the size of material, to be in the increased severity of the abrasion 

 on the soft, friable sandstone pebbles and material of a similar nature. " In 

 this test the impact of the cast-iron spheres breaks up the soft pebbles, while 

 in the stone test the Impact of the stone on stone tends merely to round off the 

 corners and edges." 



Test of wire-cut and re-pressed paving brick {Eng'm. Rec, 69 (1914), ^o. 

 22, p. 601, figs. 4)- — Experiments to compare the penetration of grout for 

 re-pressed paving brick with horizontal grooves in the end faces and for wire- 

 cut brick with double beveled or bulging ends showed that the penetrations 

 were equally satisfactory, but that the wire-cut samples formed a stronger bond 

 with the grout. 



Effect of hydrated lime on change in volume and strength of mortars and 

 concretes, H. S. Spackman (Nat. Lime Manfrs. Asf^oc. Bid. 10 (1914), PP- 24, 

 figs. 9; Concrete-Cement Age, 4 (1914), No 3, pp. 112-116, figs. 9).— The results 

 of tests on the effect of different conditions of exposure with and without the 

 addition of hydrated lime on the change in volume of Portland cement mortar 

 and concrete and on their tensile and compressive strengths are reported. 



Variation in moisture content affected the volume of the test piece more 

 than change In temperature. When kept from contact with water other than 

 atmospheric moisture there was a marked tendency to shrinkage of the test 

 piece, which continued up to and beyond the 6-month period. Where the test 

 piece was in constant or frequent contact with water it tended to expand in 

 volume. With the draining off of excess gaging water there was a marked 

 shrinkage at the 24-hour period, followed in some cases by expansion at 4^ 

 hours and further shrinkage if test specimens were out of contact with water 

 and expansion if in contact with water. The addition of hydrated lime, while 

 increasing somewhat the maximum exi^ansion and contraction when the test 

 64822°— No. 7—14 7 



