540 STUDIES FOR STUDENTS 



sandstone samples have more of the exterior grains loosened 

 in preparation than do the granite, rhyolite, and limestone. It 

 is very probable that had these same samples been subjected to 

 a second period of alternate freezing and thawing, the granite, 

 limestone, and sandstone would have agreed more nearly in the 

 loss by weight. 



Loss in crushing strength. — The result of alternate freezing and 

 thawing is more clearly manifested by a decrease in the crush- 

 ing strength of the rock than by the loss in weight. It is very 

 evident that if a stone having sub-capillary pores is subjected 

 to alternate freezing and thawing for a considerable period, the 

 adhesion of the particles will be weakened and the cement 

 perhaps shattered or broken. This will not necessarily occasion 

 an immediate loss in weight, but must necessarily decrease the 

 strength of the stone. The samples which were subjected to 

 alternate freezing and thawing for thirty-five days were broken 

 in a testing machine to determine their crushing strength. The 

 crushing strength thus obtained was compared with the crushing 

 strength obtained from the samples of fresh stone. With a few 

 explainable exceptions, the crushing strength of the frozen 

 samples of granite was much less than that of the fresh. The 

 crushing strength of the frozen samples from ten different 

 granite quarries was less than the crushing strength of the fresh 

 samples by from 2201 pounds to 13,075 pounds per square inch. 

 In the case of limestone samples from eleven different quarries 

 the frozen samples from eight showed a loss in crushing strength 

 of from 571 pounds to 18,714 pounds per square inch. Among 

 the frozen samples of sandstone from ten different quarries, six 

 gave crushing strength tests which ranged from 326 to 6264 

 pounds per square inch lower than the crushing strength of 

 the fresh samples. The average loss for all the frozen sam- 

 ples of each kind of rock is given in Table VII. Table VIII 

 gives a comparison between the average crushing strength of 

 fresh and frozen samples, and also the average loss through 

 freezing. 



