PACINI, METAMORPHISM OF PORTLAND CEMENT 



195 



TABLE 7 

 Effect of Excess of Mixing Water on Permeability of Concrete 



6 Specimens shoveled into water as described above. 



In the foregoing experiments, the decrease in strength and water- 

 tightness may be referred to the deteriorating influence of excess water 

 upon the cement (16). It may of course be argued that the more 

 marked effects obtained in series 1, 2 and 3 than in series 4 are due to 

 the method of making the tests; that is, that a considerable proportion 

 of the active cement was actually removed from the body of the concrete 

 by siphoning off the supernatant water with its laitance. 



Effect of excess of mixing water on the strength of neat cement. 

 With the idea in mind that the weakening effect was independent of the 

 removal of cement (1), a further series of tests was instituted, using a 

 neat cement of good quality. The cement was poured into a series of 

 glass tubes in which increasing proportions of water had been put, the 

 tests representing a series of grouts mixed respectively with 50, 75, 100, 

 150, 200 and 500 per cent by weight of aement of water. The tubes were 

 shaken for one hour and then allowed to stand for 28 days. The cement 

 settled into the bottom of the tubes in the order of its coarseness, the fine 

 nebulous laitance settling last as a cheesy white layer of increasing thick- 

 ness, as the percentage of water was higher. This layer was carefully 

 trimmed off in preparing the test specimens. 



On breaking out the cylinders from the tubes at the end of the test 

 period, it was decided to cut each cylinder into two, each exactly one 

 diameter high, carefully noting the respective position of each in the 

 tube. On submitting these to compression it was seen that the direction 

 of difference between the upper and lower layers was not constant, nor 



