TESTS OF WISCONSIN BUILDING STONE 527 



CRUSHING STRENGTH 



The individual test which is employed perhaps more than 

 any other to determine the strength and durability of a stone is 

 the crushing strength test. For years certain .architects and 

 builders have relied upon this test almost exclusively for form- 

 ing an estimate of the suitability of a stone for all kinds of public 

 and private buildings. This general use of the crushing strength 

 test is still prevalent in some sections of the country. 



In order to be assured of the reliability of the machine in 

 which the crushing strength tests were to be made, comparisons 

 were made with tests made in two other machines on samples 

 from the same quarries. One of the machines used was also 

 calibrated to give positive assurance of its reliability. In mak- 

 ing the tests, note was taken of the position of the sample in the 

 machine with respect to bedding or schistosity. 



Twenty-seven samples of granite from twelve different quar- 

 ries were tested. The lowest crushing strength obtained was 

 12,704 pounds per square inch, while the highest was 47,674 

 pounds per square inch. The average crushing strength of all 

 the samples tested was 27,023.7 pounds per square inch. The 

 minimum crushing strength was above the maximum crushing 

 strength obtained for sandstone, and was obtained on a sample 

 of granite gneiss in which the lamination was diagonal to the 

 direction of the pressure. As far as my knowledge extends the 

 maximum crushing strength is the highest yet recorded for any 

 rock tested in the United States. It was obtained from a sample 

 of rhyolite on which the pressure was applied normal to the head 

 or in the direction of the rift. 



It has been generally supposed that the crushing strength 

 of a stone is least in the direction of the rift or lamination, but 

 apparently this is not true in the case of the rhyolite in question. 

 This rhyolite consists of elongated crystals of feldspar and other 

 minerals in a very dense groundmass, forming what one might 

 consider a very compact bundle of fibers. A rock with such a 

 structure can apparently sustain a greater pressure when applied 

 in the direction of these fibers than when applied across them. 



