38 THE TESTIXt; OF ROAD MATERIALS. 



of the charge. Furthermore, since the loss during the earlier stages of 

 the test is mainly due to a chipping action and the subsequent loss to 

 the wearing or abrasive action of the charge, both factors of quality 

 are reported, viz, the chipping loss at 4<)0 or 800 rotations and the 

 wearing loss between 1,200 and 1,800 rotations. The form of report 

 for the rattler test is given in the Appendix. 



The rattler test for paving brick has Avon the confidence of engineers 

 after a very searching investigation extending over a number of years. 

 As now conducted, this test is constant in its action and gives valuable 

 evidence concerning the wearing qualities of brick. 



ABSORPTION TEST. 



The absorption test is valuable in determining the degree of heat at 

 which the brick was burnt. It is not, however, practicable to specify 

 a fixed per cent of absorption to which competitive samples of different 

 brands of paving brick must conform/' 



The absorptiveness of paving brick is determined in this laboratory 

 by immersing in distilled water a brick which has passed through the 

 rattler test and been thoroughly dried. The gain in weight after 

 ninety-six hours* immersion is determined and expressed in percentage 

 of the original weight of the brick. The fact that some paving bricks 

 are covered with an impervious shell makes it desirable to conduct this 

 tot on a brick whose interior structure is accessible to water: there- 

 fore, only bricks that have been subjected to the rattler test are used. 

 As far as present evidence shows, there is no serious objection to a 

 high rate of absorption on account of danger from disruption of the 

 brick through the action of frost. Defects of internal structure, 

 however, such as internal planes of division due to faulty annealing, 

 present an opportunity for the disnmtive action of free/ing water. 

 These internal faults of structure are. made evident in the rattler lot. 



( 'i:nss l',i;i;\K!N(i AND ( '< >.M Pi: l->sl< >\ 



Farilitio rxi>t in the laboratory for performing both of these tests 

 according to approved methods on the testing machines already men- 

 tioned. The core drill shown in iig. lo is available for making cylin- 

 drical tot p'uM-o of 1 (,i- -j inch diameter from the body of the brick 

 for the compreion test. Cross-breaking and compression tests are. 

 however, considered to be of secondary importance and do not furnish 

 a> Valuable evidence* of the Duality of the brick as do the rattler and 

 absorption tc>t-. 



TESTS FOB CEMENT. 



For making physical and mechanical tests on cement a Fairbanks 

 testing machine and other necessary equipment are used. The stand- 



"Sevrntrrnth Annual Report of the Illinois Society of Engineers and Surveyors,. 

 1902, p. 160. 





