PACINI, METAMORPHI8M OF PORTLAND CEMENT 



197 



TABLE 9 

 Compressive Strength of Grouts Mixed with Vaiying Proportions of Water, 



Over Extended Period 

 (Each result is the average strength of three specimens.) 



It is apparent from these figures that the effect of hydrolysis upon the 

 strength of cement is a reversible one, at least to a certain extent, since 

 the specimens in which an excess of water was used in mixing showed a 

 greater recuperative ability at the longer period than the cement in 

 which the normal amount of mixing water, in this case 22 per cent, was 

 used. 



Upon inspection, it was observed that the three months' specimens 

 showed in each case much less laitance than the similar 28 days' speci- 

 mens had shown, and it was considered probable that the laitance, in 

 standing, had adsorbed free lime from the remainder of the cement, 

 through the activity of the water permeating the mass, and thus reverted 

 to the original condition of the cement, or an approach thereto. An 

 analysis was accordingly made of laitance scraped off from the top of one 

 of the 500 per cent water specimens and thoroughly washed by decanta- 

 tion. It probably represents a maximum condition in the hydrolysis of 

 cement. 



TABLE ]0 

 Analysis of Laitance from 500 per cent Specimen 



