.Abrasion Test. This test was first used in France, and is commonly known as the Deval test, bearing the name of its designer. The Deval machine consists of cylinders 20 cm. in diameter and 34 cm. in depth, closed at one end and with a tightly fitting cover for the other. Two or four of these cylinders are mounted upon a horizontal shaft so that the axis of each cylinder is inclined at an angle of 30 degrees with the axis of rotation.
The method of conducting the test in the investiga tions of the U. S. Office of Public Roads is as follows: * "The sample to be tested is first broken in pieces that will pass in all positions through a 6 centimeter (2.4 inch) ring. The stones are then cleansed, dried in a hot-air bath at 10o degrees C., and cooled in a desiccator. Five kilograms are weighed and placed in one of the cylinders, the cover bolted on, and the machine rotated at the rate of 2000 revolutions per hour for 5 hours. When the 10,000 revolutions of the machine are com pleted the contents of the cylinder are placed on a sieve of 0.16 centimeter ( inch) mesh, and the material which passes through is again sifted through a sieve of 0.025 centimeter (o.or inch) mesh. Both sieves and the fragments of rock remaining on them are held under running water till all adhering dust is washed off. After the fragments have been dried at 100 degrees C. and cooled in a desiccator they are weighed, and their weight subtracted from the original 5 kilograms (rr pounds). The difference obtained is the weight of the detritus under 0.16 centimeter inch) worn off in the test. " In the French experiments it was found that the best grades of rock gave about 20 grams of detritus per kilogram of rock tested, and the number 20 was adopted as a standard and the " coefficient of wear " determined from the formula: in which W is the weight in grams of detritus under 0.16 centimeter (A inch) in size obtained per kilo gram (2.2 pounds) of stone. The French coefficient is sometimes used in stating results in American tests, but it is more common to ues the "percentage of wear," which is found by stating the weight of detritus under 0.16 centimeter in terms of percentage of the weight of rock tested. In this case, Percentage of wear = 40 • Coefficient of wear In some of the work of the United States Agricul tural Department another coefficient, known as the United States Agricultural Department coefficient of wear, has been employed. This coefficient is found by subtracting 400o grams from the weight of the frag ments over 3 centimeters (1.2 inches) which remain after the test and dividing the difference by 10. By this method, if 20 per cent of the material is abraded from the original 5000 grams, the coefficient is 0 and the material considered worthless; if no dust is worn off, the coefficient is 100.
The Committee on Standard Tests for Road Materials, of the American Society for Testing Materials, in 1904 recommended the following specification for the abrasion test: "The machine shall consist of one or more hollow iron cylinders, closed at one end and furnished with a tightly fitting iron cover for the other; the cylinders to be 20 centimeters in diameter and 34 centimeters in depth inside. These cylinders are to be mounted on a shaft at an angle of 30 degrees with the axis of rotation of the shaft. .
"At least 30 pounds of coarsely broken stone should be available for a test. The rock to be tested should be broken in pieces as nearly uniform as possible, and as nearly 5o pieces as possible shall constitute a test sample. The total weight of rock in a test should be within 10 grams of 5 kilograms. All test pieces should be washed and thoroughly dried before weighing; 10,000 revolutions at the rate of between 3o and 33 to the minute, must constitute a test. Only the per centage of material worn off which will pass through a 0.16 centimeter mesh sieve should be considered in determining the amount of wear. This may be expressed either in the per cent of the 5 kilograms used in the test, or the French coefficient, which is in more general use, may be given." Cementation Test. This test was developed by Mr. Logan Waller Page while geologist of the Mas sachusetts Highway Commission. It consists in grind ing the stone into dust, and moulding the dust into a small cylinder, which is dried and then tested by subjecting it to the impact of the falling weight. The method of conducting this test as used by the Office of Public Roads of the United States Department of Agriculture is as follows: "One kilogram of the rock to be tested is broken sufficiently small to pass a 6 millimeter but not a i millimeter screen. It is then placed in a ball mill and is ground for two hours and a half. This ball mill contains two chilled iron balls which weigh 25 pounds each, and is revolved at the rate of 2000 revolutions per hour. It was found by experiment that grinding rock thus pre pared for two hours and a half was sufficient to reduce it to a powder that would pass through a 0.25 milli meter mesh. The dust thus obtained is mixed with water to about the consistency of a stiff dough, and is kept in a closed jar for twenty-four hours. About 25 grams of this dough is placed in a cylindrical metal die 25 millimeters in diameter. A closely fitting plug, supported by guide rods, is inserted over the material, which is then subjected to a pressure of zoo kilograms per square centimeter.