46 
BULLETIN 1132, U. S. DEPAETMENT OF AGRICULTURE. 
CRUSHING STRENGTH OR COMPRESSION TEST. 
This test is made upon a cylindrical test specimen 2 inches in 
diameter and 2 inches high. Both ends of the specimen, which 
have been sawed at right angles to the axis of the cylinder, are 
carefully ground to plane surfaces. The cylinder then is crushed 
in a 200,000-pound Universal testing machine at a speed of 0.1 inch 
per minute. A small 2-inch spherical bearing block is placed between 
the moving head of the machine and the specimen. The average 
of at least two determinations is reported as the crushing strength, 
calculated in pounds per square inch. Crushing strength tests are 
made only when specifically requested. 
INTERPRETATION OF RESULTS OF PHYSICAL TESTS. 
To interpret the results of the physical tests of road-building 
rock, the Bureau of Public Roads has adopted a table of general 
limiting test values for broken stone for the various types of road 
construction. For general reference, these limiting values, together 
with comments upon limits shown, are given in Table 3. By com- 
paring the results of tests on a sample of rock with the limits shown 
in the table a general idea of the types of road construction* for 
which it is best suited may be obtained. It must be emphasized, 
however, that these values represent average conditions only. For 
any given material a number of factors such as type of stone, character 
and volume of traffic, and the character of available material will 
influence the interpretation to be given the results of the tests. 
Table 4 contains the total number of rock samples received from the 
various States which have been tested between January 1, 1916, 
and December 31, 1921. 
Table 2. — Results of compression tests of rock, made prior to Jan. 1, 1916. 
ARKANSAS. 
Serial 
County. 
Name. 
Crushing 
strength 
pounds per 
squareinch. 
6331 
Bald Knob. 
White Sandstone 
CONNECTICUT. 
9791 Oneco. 
Windham Biotite granite 
16,635 
ILLINOIS. 
4422 
Coles 
Limestone 
Dolomite 
do 
17,300 
23,060 
16, 880 
5509 
Cook 
6053 
.do 
do 
8711 
Hillside . 
....do 
Argillaceous dolomite 
15,730 
19, 150 
4660 
Tunnel Hill 
7509 
.do 
Argillaceous limestone 
25,780 
28,400 
20, 610 
17,710 
20,830 
11,660 
7510 
do 
do 
. . .do 
4764 
Dolomite 
5550 
do 
do 
do 
6088 
do 
do 
Argillaceous dolomite 
6165 
do .... 
...do 
Dolomite 
6865 
do 
do. . 
do 
...do 
do 
13,500 
7298 
Argillaceous dolomite 
25,850 
7299 
do 
do - 
... .".do 
20.000 
7300 
.!...do 
do 
do 
19,008 
