UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 670 
- Contribution from Office ofPublic Roads and Rural Engineering, r^l 
J&f'^JU LOGAN WALLER PAGE, Director. S&M&sL 
Washington, D. C. 
PROFESSIONAL PAPER 
June 14, 1918 
THE RESULTS OF PHYSICAL TESTS OF ROAD- 
BUILDING ROCK IN 1916 AND 1917. 
By Prevost Hubbard, Chemical Engineer, and Frank H. Jackson, Jr., Assistant 
Testing Engineer. 
CONTENTS. 
Crushing strength or compression test 1 
Interpretation of results of physical tests 2 
Table I.— Results of physical tests of road- 
building rock in 1916 and 1917 3 
Table II.— Results of compression tests of 
rock made prior to January 1, 1916 24 
2.S 
Table III.— Geographical distribution of rock 
samples tested to January 1, 1918 
Table IV. — General limiting test values for 
broken stone 29 
This bulletin supersedes United States Department of Agriculture 
Bulletin 537 and supplements Bulletin 370, which gives the results 
of the more common physical tests of some 3,650 road-building rock 
samples, examined prior to January 1, 1916. Tests of 655 additional 
samples examined in 1916 and 1917 are recorded in Table I, the rocks 
being classified as to their location. It will be noted that in a number 
of cases, in addition to other tests, the crushing strength of the rock 
also is given. This test is not made ordinarily when examining rock 
to determine its suitability for use in the various types of broken- 
stone roads, but is employed often when considering a rock for use 
in the manufacture of paving block or as railroad ballast. Table II 
gives a complete record of all of the crushing strength tests made 
by the office prior to January 1, 1916. A brief description of this 
test as made by the office follows. 
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, and 
properly faced, are bedded in plaster of Paris. The cylinder then 
is crushed in a 200,000-pound universal testing machine. A small 
2-inch spherical bearing block is placed between the moving head 
of the machine and the upper surface of the specimen. The aver- 
age of at least two determinations is reported as the crushing strength, 
calculated in pounds per square inch. Crushing strength tests are 
made upon samples of road-building rock only when specifically 
requested. 
46175°— 18— Bull. 670 1 
