SAMPLING AND TESTING HIGHWAY MATERIALS. 7 
ABRASION TEST FOR GRAVEL. 
(1) The aggregate shall first he screened through screens hav- Test sample. 
ing circular openings 2 inches, \\ inches, 1 inch, three-quarters 
inch, and one-half inch in diameter. The material of these sizes 
shall he washed and dried. The following weights of the dried 
stone shall then he taken: 1.250 grams of the size passing the 
2-inch and retained on the 1^-ineh screen, 1,250 grams of the size 
passing the 1^-inch and retained on the 1-inch screen. 1,250 grams 
passing the 1-inch and retained on the three-quarters inch screen, 
1.250 grams passing the three-quarters inch and retained on the 
one-half inch screen. This material shall be placed in the cast- 
iron cylinder of the Deval machine as specified for the stand- 
ard abrasion test on stone. Six east-iron spheres 1.875 inches in 
diameter and weighing approximately 0.95 pound (0.45 kilogram) 
each shall be placed in the cylinder as an abrasive charge. These 
spheres are the same as those used in the standard rattler test 
for paving brick. 
(2) The duration of the test and the rate of rotation shall be Duration 
the same as specified for the standard test for stone, namely, of test. 
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 one-sixteenth inch mesh sieve. The material 
retained upon the sieve shall be washed and dried and the per- 
centage loss by abrasion of the material passing the one-sixteenth 
inch mesh sieve calculated. 
(3) When the material has a specific gravity below 2.20 a 
total weight of 4.000 grams made up of the four groups of sizes 
described above, instead of 5,000 grams, shall be used in the 
abrasion test. 
TEST FOR TOUGHNESS OF ROCK. 
(A. S. T. M. standard method, serial designation D 3-18, slightly 
modified.) 
1. The term " toughness," as applied to rock, is defined as the 
resistance offered to fracture under impact, expressed as the fall 
in centimeters of a standard hammer which, after a series of 
blows from increasing heights, finally causes fracture of a cylin- 
drical test specimen of given dimensions. 
2. Quarry samples of rock from winch test specimens are to Size of sample. 
be prepared shall measure at least f> inches on a side and at 
least 4 inches in thickness, and when possible shall have the 
plane of structural weakness of the rock plainly marked thereon. 
Samples shall be taken from freshly quarried material, and only 
from pieces which show no evidences of incipient fracture due 
to blasting or other causes. The samples shall preferably be 
split from large pieces by the use of plugs and feathers and 
not by sledging, commercial stone-block samples from which 
test specimens are to be prepared shall measure at least .". inches 
on each edge. 
3. Specimens for testing shall be cylinders prepared as de- Preparation 
scribed in section 4. 25 millimeters in height and from 24 to 25 of specimen. 
millimeters in diameter. Three test specimens shall constitute 
a test set. The ends of the specimen shall be plane surfaces ai 
right angles to the axis of the cylinder. 
4. One set of specimens shall be drilled perpendicular and an- 
other parallel to the plane of structural weakness of the rock, 
if such plane is apparent. If a plane of structural weakness is 
not apparent, one set of specimens shall be drilled at random. 
Specimens shall be drilled in a manner which will not subject 
the material to undue stresses and which will insure the specified 
