PACINI, METAMORPHISM OF PORTLAND CEMENT 



203 



the action of the water upon the cement, two cases alone will be con- 

 sidered. 



The rock was crushed and screened for each experiment to the same 

 average effective size, corresponding to the following mechanical analysis : 



TABLE 13 

 Mechanical Analysis of Aggregate used in Permeability Tests 



The sieve ratings are based on diameters of spheres of equivalent vol- 

 ume to the largest sized stone particles that will pass. 



The fine aggregate was crushed quartz, the standard sand formerly 

 used for cement testing, passing the Xo. 20 and retained on the Xo. 30 

 sieve. The cement used was a standard Portland of high quality. 



The specimens were made in the laboratory's standard form for per- 

 meability test, cylinders eight inches in diameter and six inches in length, 

 the proportions used being 1 : 3.5 : 6, this being found the richest mix 

 practicable to secure the porosity required for the test. They were cased 

 in neat cement, and connected suitably for subjection to the pressure of 

 the city's water mains. Each specimen was protected from the direct 

 flow of the water by a layer of one inch of clean coarse sand. The average 

 pressure for the period of observation (52 weeks) was 22 pounds. The 

 determinations of the rate of leakage were made weekly at first, and later 

 every two weeks until the end of the test. 



The data appended below represent observations on the rate of percola- 

 tion of water through two of the specimens which present the greatest 

 interest from the standpoint of this paper, this flow being recorded in 

 grams passing in ten minutes. The aggregate used in one specimen was 

 a hardened neat cement, crushed to the size stated, and used in place of 

 the rock generally employed in concrete. The parallel specimen selected 

 for comparison was one in which the aggregate was a crushed granite, 

 which showed a low solubility in hydrochloric acid (2.66 per cent dis- 

 solved in one hour's treatment with 1 : 1 HC1). 



