RURAL ENGINEERING. Vgl 



Wearing- tests for sand and gravel, F. L. Roman (Good Roads, n. ser., 9 

 (1915), No. 18, pp. 183, 187).— This article describes two tests of the wearing 

 qualities of aggregates which have been used in the laboratory of the Illinois 

 highway department. 



The wearing test for sand consists essentially of submitting a given weight of 

 sand to the wearing effect of an ordinary Deval abrasion machine, the cast-iron 

 cylinders of which contain a certain weight of small steel shots. After 1,000 

 revolutions at 30 to 33 per minute the material passing a 100-mesh sieve is 

 considered as the wear. Data from a number of such tests show practically no 

 wear in the case of Ottawa sand and very little wear in the case of sands 

 composed mainly of quartz. The mixed sands show average wearing qualities 

 while the limestone sands give the poorest wear. 



The wearing test for gravel is also performed in the Deval abrasion machine. 

 No shots are used, the wear being caused by the grinding of the stones against 

 each other and the sides of the cast-iron cylinders. 



Effect of fineness of sand and of clay and loam on the strength of mortar, 

 F. L. Roman (Engin. and Contract., 43 (1915), No. 18, pp. 403-406, figs. 10).— 

 Tests made by the Illinois highway department on the effect of various per- 

 centages of fine sand below 50-mesh on the strength of mortar, with particular 

 reference to highway structures, brought out the following conclusions : 



" In a well-graded sand the presence of fine material passing the No. 50 sieve 

 causes a decrease in the strength of its 1 : 8 mortar, the strength of the 1 : 3 

 mortar obtained from the portion of the same sand retained on the No. 50 sieve 

 being taken as the basis of comparison. In a badly graded sand the presence 

 of a small proportion of clean sand passing the No. 50 sieve might probably, 

 under certain conditions, cause a slight increase in the strength of the mortar, 

 but the presence of a large proportion of the material passing a 50-mesh sieve 

 will cause a decrease in strength. . . . 



" Small amounts of clay in sand seem to cause a small increase in the 

 strength of the mortar. The tensile strength curve of 1 : 3 mortar briquettes 

 in which the sand contains increasing percentages of clay rises at first with 

 small quantities of clay. With larger quantities of clay, however, the strength 

 begins to drop. . . . 



" Organic loam in sand, even in very small quantities, will cause a decrease 

 in the strength of the mortar. In the tests IJ per cent of organic matter in 

 sand caused a decrease in the tensile strength of 1 : 3 mortar of 15 to 20 per 

 cent. Often 1 per cent and sometimes 2 or 3 per cent of organic matter in 

 sand can not be detected in the general appearance of the sand, and whenever 

 the sand appears dark and loamy it is a sure sign that it should be tested before 

 using in concrete work." 



Concrete road with a single crack in 4i miles, the result of careful con- 

 struction (Engin. Rec, 71 (1915), No. 16, pp. 480-482, figs. 11).— A description 

 of the construction of 41 miles of concrete road which has stood for one year witli 

 only one crack is given. Features in the construction were thorough rolling of 

 the subgrade, adequate provision for drainage, minimum time for mixing each 

 batch of concrete, careful grading of sand, accurate measurement of concrete 

 materials in boxes, and use of wire-mesh reinforcement. 



The concrete road is single course, 18 ft. wide, 8 in. thick at the center, and 6 

 in. thick at the sides. The foundation is an old macadam road and the maxi- 

 mum grade 5.8 per cent. The contract cost was $15,914 per mile. 



Brick highways in King County, Washington, F. W. Allen (Municipal 

 Jour., 37 (1914), No. 23, pp. 795-799, figs. 8). — This article gives data regarding 

 the cost, methods of construction, and methods and results of tests of materials 

 for brick-surfaced country roads to withstand a heavy rural traffic. 



