UNITED STATES DEPARTMENT OF AGRICULTURE 



1? BULLETIN No. 537 



# -Si 



i4£* Contribution from Office of Public Roads and Rural Engineering, r^l 

 SZ&&SL LOGAN WALLER PAGE, Director. ^V^"^fe» 



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. 



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 22 



Table IV. — General limiting test values for 

 broken stone 23 



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 



