30 BULLETIN 555, U. S. DEPARTMENT OF AGRICULTURE. 



RECOMMENDED STANDARD METHODS OF TESTING MATERIALS. 



TESTS OF PHYSICAL PROPERTIES OF STONE, SLAG, GRAVEL, 



AND SAND. 



(1) Abrasion Test (pee cent of Wear, ob French Coefficient of Wear), 

 Stone, Stone Block, and Slag : United States Department of Agriculture Bulle- 

 tin 347, page 5. 



Notes. — (a) Attention is directed to the fact that tests of rock and slag 

 for abrasion by the use of the Deval machine are not entirely satisfactory. 

 The formation of a dust cushion in the cylinder partially prevents the abrasion 

 of the stone. Sufficient data are not at hand to show the amount of wear when 

 this dust cushion is removed after intervals of time. 



(6) It is hoped that laboratories will take up this test with the idea of de- 

 veloping a coefficient of wear more nearly representative of the actual resist- 

 ance of the stone. 



(c) It is desired to call attention to the fact that two methods of preparing 

 the stone or slag are in use — viz, hand breaking and machine breaking, and 

 furthermore to recommend that arrangements be made between States for con- 

 ducting check tests for abrasion on portions of the same sample. 



(d) In testing light stone and light slag, it is recommended that some stand- 

 ard volume be substituted for the standard weight of 5.000 grams. 



(e) In the case of stone block it is recommended that the laboratories co- 

 operate to devise new methods of testing stone block to determine their suita- 

 bility for pavements. 



(2) Abrasion Test. Suggested for Gravel: 



The aggregate is screened first through screens having circular openings 2 

 inches, 1 inch, and 1 inch in diameter. The sizes used for this test are divided 

 equally between those passing the 2-inch and retained on the 1-inch screen, 

 and those passing the 1-inch and retained on the ^-inch screen. The material 

 of these sizes is washed and dried. The following weights of the dried stone 

 are then taken : 2,500 grams of the size passing the 2-inch and retained on 

 the 1-inch screen, and 2,500 grams of the size passing the 1-inch and retained 

 on the £-inch screen. This material is placed in the cast-iron cylinder of the 

 Deval machine as specified for the standard abrasion test on stone. Briefly de- 

 scribed, this machine consists of a frame and two or more cylinders mounted 

 at an angle of 30° with the axis of rotation. The cylinders are of the following 

 size : 20 cm. diameter by 31 cm. deep, inside dimensions. Six cast-iron spheres 

 1.875 inches in diameter and weighing approximately 0.95 pound (0.45 kg.) 

 each, are placed in the cylinder as an abrasive charge. The iron composing these 

 spheres, which are the same as those used in the standard paving brick rattler 

 test, has the following limits of composition : 



Combined carbon, not under 2.50 per cent. 



Graphitic carbon, not over 0.25 per cent. 



Silicon, not over 1.00 per cent. 



Manganese, not over 0.50 per cent. 



Phosphorus, not over 0.25 per cent. 



Sulphur, not over 0.08 per cent. 

 After the cast-iron spheres have been placed in the cylinder the lid is bolted 

 on and the cylinder mounted in the frame of the Deval machine. The dura- 

 tion of the test and the rate of rotation are the same as specified for the stand- 

 ard test for stone, namely, 10.000 revolutions at a rate of 30 to 33 revolutions 

 per minute. At the completion of the test the material is taken out and 

 screened through a 16 mesh sieve. The material retained upon the sieve is 

 washed and dried and the per cent loss by abrasion of the material passing 

 the 16 mesh sieve calculated. 



