SAMPLING AND TESTING HIGHWAY MATERIALS. 63 



ably divided into three portions for sieving, the sieving being completed over a sheet 

 of white paper, and is continued until practically no dust passes the sieve when 

 shaking for one minute. The portion retained on the 100-mesh sieve is weighed. 

 Five hundred grams minus the weight of the samples retained on the 100-mesh after 

 abrasion is taken as the loss from abrasion. This weight divided by 5 gives the per- 

 centage of wear. 



44. PROPOSED FIELD METHODS OF MAKING SIEVE ANALYSIS. 



Either volumetric or gravimetric methods may be used on a sample of not less than 

 500 grams in the volumetric or 200 gram.s in the gravimetric test. The following 

 methods for making these tests are suggested: 



A. VOLUMETRIC METHOD. 



Briefly described, the apparatus for this test consists of an outside cylindrical con- 

 tainer with telescopic cover, two nests of semicylindrical screens and sieves fitting 

 into the outside cylinder and containing a smaller cylinder with telescopic cover. 

 This small cylinder contains in turn a 10-inch rule having Yg-LQch divisions and a 200 

 c. c. graduated cylinder. The entire outfit is very compact, measuring about 14 

 inches in length and 5 inches in diameter. 



Both the outer and inner cylinders are exactly 10 inches in inside depth, the tele- 

 scopic covers being made to fit the contents of each cylinder. As used at present, 

 there are in each outfit five screens having circular openings lj-inch, 1-inch, f-inch, 

 i-inch, and |-inch in diameter, respectively, and three sieves of standard 10-mesh, 

 20-mesh, and 50-mesh, respectively; also three rings of 3-inch, 2J-inch, and 2-inch 

 diameter, respectively, fitting in the cover of the container. 



The large cylinder is used when making a screen analysis of a coarse aggregate, 

 while the small cylinder is used in determining the gradation of sand or other fine 

 aggregate. The cylinder is filled with the material to be examined, which is then 

 screened through the screen, or sieve, selected. The portion passing the screen, or 

 sieve, is returned to the cylinder and the height of the material determined, each 0.1 

 inch corresponding to 1 per cent of the original volume. The portion retained on the 

 screen, or sieve, is determined in the same manner. The percentage passing plus 

 the percentage retained when obtained in this manner add up to more than 100 per 

 cent of the original volume, and if the true percentage passing each screen or sieve is 

 to be reported, the correct value is obtained by dividing the percentage passing each 

 screen or sieve as found above by the total of the measurements obtained for material 

 retained and material passing the screen or sieve. For example, if a gravel shows by 

 measurement 60 per cent retained on a 1-inch screen and 50 per cent passing a 1-inch 

 screen, the true percentage passing the 1-inch screen is — 



50 50 

 60+50 = TT0 =4 °* P er cent " 



B. GRAVIMETRIC METHOD. 



The apparatus required consists of a spring balance, 200-grams capacity, graduated 

 to tenth-gram divisions and provided with a weighing pan; a series of field sieves 

 well graded in size from a ^-inch screen to a standard 200-mesh sieve. The sample, 

 selected in accordance with the method described, shall be dried in the air or by heat- 

 ing to not over 110° C. The sample for sieve analysis shall be selected from the dried 

 sample by the method of quartering and shall weigh approximately 200 grams. This 

 sample shall be passed successively through the various screens required and the total 

 percentage passing each sieve shall be reported. 



