4 BULLETIN 370, U. S. DEPARTMENT OF AGEICULTURE. 



I TOUGHNESS TEST. 



Toughness is determined by subjecting a cylindrical test specimen 

 25 by 25 millimeters (1 by 1 inch) in size to the impact produced by 

 the fall of a 2-kilogram (4.4-pound) hammer upon a steel plunger 

 whose lower end is spherical and rests upon the test piece. The 

 energy of the blow delivered is increased by increasing the height of 

 fall of the hammer 1 centimeter (0.39 inch) after each blow. The 

 height of blow in centimeters at failure of the specimen is called the 

 toughness. 



DEVAL ABRASION TEST. 



A test devised by the French for measuring the combined action 

 of abrasion and impact is as follows: Five kilograms (11 pounds) 

 of freshly broken rock between 2 and 2| inches in size is tested in a 

 special form of cylinder so mounted on a frame that the axis of 

 rotation of the cylinder is inclined at an angle of 30° with the axis 

 of the cylinder itself. The fragments of rock forming the charge 

 are thus thrown from end to end twice during each revolution, caus- 

 ing them to strike and rub against each other and the sides of the 

 cylinder. After 10,000 revolutions the resulting material is screened 

 through a yV-ii^ch sieve and the weight of the material passing is used 

 to calculate the per cent of wear. The French coefficient of wear is 

 calculated from the per cent of wear as follows : 



40 



French coefficient of wear==n 1 • 



1 er cent wear 



CEMENTING-VALUE TEST. 



To determine the binding power, or cementing value, as it is usually 

 called, 500 grams (1.1 pounds) of the material to be tested is crushed 

 to pea size and ground with water in a ball mill until it has the con- 

 sistency of a stiff dough. It is then molded into cylindrical briquettes 

 25 by 25 millimeters (1 by 1 inch) in size, Avhich, after thorough dry- 

 ing, are tested to destruction in a special form of impact machine. 

 A 1-kilogram (2.2-pound) hammer falls through a constant height 

 of 1 centimeter (0.39 inch) upon an intervening plunger, which in 

 turn rests upon the test piece. By means of a suitable arrangement a 

 graphic record of the number of blows required to destroy the speci- 

 men is obtained. The number of blows producing failure is called 

 the cementing value of the material. 



SPECIFIC GRAVITY— WEIGHT PER CUBIC FOOT— WATER ABSORPTION. 



The specific gravity, weight per cubic foot, and the water absorp- 

 tion in pounds per cubic foot are obtained on samples of rock which 

 are tested to determine their road-building qualities. The weight 



