UNITED STATES DEPARTMENT OF AGRICULTURE 



BULLETIN No. 670 



1%? ContributionfromOfliceofPublicRoadaand Rural Engineering, n^l 

 j^HjSjj^ LOGAN WALLER PAGE, Director. 



Washington, D. C. PROFESSIONAL PAPER June 14, 1!)J8 



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. 



Page. 



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 



Table III.— Geographical distribution of rock 

 samples tested to January 1, 1918 28 



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 



