BRICK ROADS. 7 



specimen brick are subjected to destructive influences very similar to 

 those encountered in actual service, and the results obtained, there- 

 fore, indicate very closely the effect which traffic may be expected to 

 produce on a pavement constructed of similar brick. The methods 

 of making the test, of Avhich there were formerly a great many, have 

 undergone repeated changes in order that service conditions may be 

 more nearly approached, and also in an effort to bring about uni- 

 formity, so that the results obtained may be of the greatest possible 

 scientific value. The method which is now proposed by the sub- 

 committee on paving brick of the American Society for Testing 

 Materials may be briefly described as follows: 



The apparatus necessary for making the test, ordinarily called 

 the rattler, consists of a 14-sided barrel of regular polygonal cross 

 section supported on a suitable frame and fitted with the necessary 

 driving mechanism. The staves, each of which forms a side of the 

 barrel, are made of 6-inch 15.5-pound structural steel channels 27^ 

 inches long. These staves are double bolted to the cast-iron heads 

 of the barrel, which are provided with slotted flanges for holding 

 the bolts. Cast-iron wear plates are bolted to the inside of the 

 barrel heads. The inside diameter of the barrel is 28f inches. 



In this barrel is placed what is laiown as the abrasive charge. 

 This charge consists of two sizes of cast-iron spheres having respec- 

 tive diameters of 3f inches and IJ inches and weighing, respectively, 

 7.5 pounds and 0.95 pound when new. Ten of the larger spheres are 

 used, and the number of the smaller spheres is made such that the 

 weight of the entire charge will approximate 300 pounds. The indi- 

 vidual larger spheres are discarded whenever their weight falls to 

 7 pounds or less and the smaller spheres when they become sufficiently 

 worn by usage to pass through a circular opening having a diameter 

 of If inches. 



The test is made by placing a charge of 10 dry brick in the barrel, 

 together with the abrasive charge, and then revolving the barrel 1,800 

 times. The number of revolutions per minute is not permitted to fall 

 below 29^ nor to exceed 30|, and the operation is made continuous 

 from start to finish. 



The results of the test are reckoned in terms of the loss in weight 

 sustained by the brick, and this loss is expressed as a percentage of 

 the original weight of the brick tested. In determining the loss in 

 weight, no piece of brick which weighs less than 1 pound is considered 

 as having withstood the test. 



Good paving brick will ordinarily lose from 18 per cent to 24 per 

 cent of their original weight in the rattler test, and specifications con- 

 cerning this loss should be prepared with a view to the character of 

 the traffic for which the pavement is designed. 



