METHODS OF SAMPLING ANT) TESTING HIGHWAY MATERIALS 19 
subject the material to undue stresses and which will insure the specified 
dimensions. The ends of the cylinders may be sawed by means of a band or 
diamond saw, 10 or in any other way which will not induce incipient fracture, 
but shall not be chipped or broken off with a hammer. After sawing, the 
ends of the specimens shall be ground plane with water and carborundum or 
emery on a cast-iron lap until the cylinders are 25 millimeters in length. 
6. The test shall consist of a 1-centimeter fall of the hammer for the first 
blow, a 2-centimeter fall for the second blow, and an increase of 1-centimeter 
fall for each succeeding blow until failure of the test specimen occurs. 
7. The height of the blow in centimeters at failure shall be the toughness 
of the test specimen. The individual and the average toughness of three test 
specimens shall be reported when no plane of structural weakness is apparent. 
In cases where a plane of structural weakness is apparent, the individual 
and average toughness of the three specimens in each set shall be reported and 
identified. Any peculiar condition of a test specimen which might affect the 
result, such as the presence of seams, fissures, etc., shall be noted and recorded 
with the test result. 
6. METHOD OF TEST FOk TOUGHNESS OF GRAVEL 
The material to be tested is accurately quartered until a sample is obtained 
which contains at least 50 pieces, ranging in size from three-quarters inch to 
2 inches in diameter. Care should be taken to see that the various sizes 
appear in about the same proportion as in the original sample. The pieces 
thus obtained are then tested individually by first determining the average 
diameter across the shortest dimension and then subjecting each to a single 
blow of the hammer, using the machine described in a paper printed in the 
Proceedings of the American Society for Testing Materials for 1922, entitled 
"An impact test for gravel." by F. H. Jackson, Bureau of Pubic Roads (11). 
Note. — It is suggested that the height of fall shall be that indicated in the following 
table : 
Diameter 
of 
particle 
Height of fall 
Sedi- 
mentary 
origin 
Igneous 
or meta- 
morphic 
origin 
Inches 
% 
1 
1M 
Inches 
2 
3 
4 
5 
Inches 
3 
4 
5 
6 
Failure in this test shall be construed as the actual crushing or splitting of a 
fragment under a single blow of the hammer. 
7. METHOD OF DETERMINING QUALITY OF GLACIAL 
GRAVELS BY LITHOLOGICAL COUNT OF PARTICLES 
From 100 to 200 pieces of gravel stones, selected at random, ranging in size 
from one-half inch to two inches, shall be separated into the various rock types 
and the percentage composition noted. 
Note. — This is a simple test which, especially in dealing with the northern glacial 
gravels, will obviate considerable laboratory work. There is no single laboratory test 
for this type of material which will give such conclusive results as to quality of the 
material as this when the adjacent bedrock and direction of the glaciation are known. 
"The form of diamond drill described in Department Bulletin No. 347, U. S Department 
of Agriculture (10, p. 6-7), is recommended, and should prove satisfactory if the instruc- 
tions are strictly followed. 
10 A satisfactory form of diamond saw is described in Department Bulletin No. 347, 
L. S. Department of Agriculture (10, p. 
