UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 537 
Contribution from Office of Public Roads and Rural Engineering 
J&f<$&U LOGAN WALLER PAGE, Director. 
Washington, D. C. 
PROFESSIONAL PAPER 
April 21, 1917 
THE RESULTS OF PHYSICAL TESTS OF ROAD- 
BUILDING ROCK IN 1916, INCLUDING ALL COM- 
PRESSION TESTS. 
By Prevost Hubbard, Chemical Engineer, and Frank H. Jackson, Jr., Assistant 
Testing Engineer. 
CONTENTS. 
Page. 
Introduction 1 
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 3 
Table II. — Results of compression tests of 
rock to January 1, 1917 17 
Table III.— Geographical distribution of rock 
samples tested to January 1, 1917 
Table IV.— General limiting test values for 
broken stone 
22 
INTRODUCTION. 
This bulletin should be considered as a supplement to United 
States Department of Agriculture Bulletin 370, which gives the 
results of the more common physical tests of some 3,650 road- 
building rock examined by the Office of Public Roads and Rural 
Engineering to January 1, 1916. The office tested 396 samples of 
rock in 1916, the results of which tests are given in Table I, the rocks 
being classified according to their location. It should 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 ex- 
amining rock to determine its suitability for use in various types 
of broken-stone roads. The test is employed often, however, when 
considering a rock for use in the manufacture of paving block, and 
as many requests for records of the crushing strength of various 
rocks have been received in the past year, it has been thought advis- 
able to give in Table II a complete record of all of the crushing- 
strength tests made by the office up to January 1, 1917. Following 
is a brief description of this test, as made by the office. 
CRUSHING STRENGTH OR COMPRESSION TEST. 
The compression 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, 
81335°— Bull. 537—17 1 
