METHODS OF SAMPLING AND TESTING HIGHWAY MATERIALS 17 
should be taken that the temperature be low enough to prevent injury to the 
stone through heat. 
4. METHOD OF TEST FOR ABRASION OF GRAVEL 
A. TEST FOR GRAVEL CONTAINING NO CRUSHED PIECES 
1. The sample shall consist entirely of uncrushed fragments of gravel, and 
the test shall be made using one of the four gradings (A, B, C, or D) given in 
paragraph 3. The grading most nearly representing that of the material fur- 
nished for the work shall be selected for the test. 
2. The aggregate shall first be screened into the different sizes required for 
the' test, and the material of these sizes shall be washed and dried. 
3. The sample shall consist of 5.000 grams of the dry gravel, with the dif- 
ferent sizes combined to conform to one of the following four gradings : 
Table 2. — Gradings of gravel 
Size of screens (cir- 
cular openings) 
Percent- 
Grading 
Passing 
Retained 
on 
age 
\ __ 
Inch 
1 * 
1 ,* 
i ?* 
{ A 
Inch 
A 
1 
A 
% 
i 
A 
% 
V* 
A 
25 
25 
25 
25 
25 
25 
B 
c 
50 
50 
D 
50 
50 
50 
4. The sample for the test shall be placed in the cast-iron cylinder of the 
Deval abrasion-testing machine as specified for the standard abrasion test for 
stone. Six cast-iron spheres 1.875 inches in diameter and weighing approxi- 
mately 0.95 pound (0.45 kilogram) each shall be placed in the cylinder as an 
abrasive charge. 7 
5. The duration of the test and the rate of rotation shall be the same as 
specified for the standard 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 
shall be taken out and screened over a No. 12 sieve, conforming to the require- 
ments of the standard specifications for sieves for testing purposes of the 
American Society for Testing Materials (serial designation B 11-26 (3)). The 
material retained upon the sieve shall be washed, dried, and weighed. The 
difference between this weight and the weight of the original sample, expressed 
as a percentage of the original weight, shall be considered as the loss by 
abrasion. 
6. When the gravel has a specific gravity below 2.20, a sample of 4.000 grams. 
instead of 5,000 grams, shall be used for the test. The testing procedure shall 
be the same in all other respects. 
7. When the gravel, as used in the work, contains as much as 25 per cent of 
material finer than one-half inch, but is of such size that either grading 
A, B, or C would be used for the abrasion test, a second abrasion test shall be 
made, using grading D, if, in the opinion of the engineer, the particles finer 
than one-half inch are not at least equal in hardness to those coarser than 
one-half inch. 
7 These spheres are the same as those used in the standard rattler test for paving brick. 
104022°— 28 2 
