2017 Volume 71 Issue 1 Pages 40-47
This paper describes the role of Portlandite on the hydration of C3A -Gypsum -Portlandite system. Their solid phase was measured by XRD Rietveld analysis and 27Al MAS NMR measurement, and liquid phase was measured by ICP-AES and ion chromatograph. As a result of measurement, two things are confirmed as an effect of the addition of Portlandite. The first one is the amount of amorphous C4AH13 increases at the initial stage of hydration. Second one is the presence phase of amorphous C4AH13 is attracted to the C3A particle surface and shrinks. From the above, the C4AH13 thin film deposited on the C3A particle surface densifies and delay the C3A hydration reaction after thin film formation. In addition, prediction of C3A hydration was performed by using a phase equilibrium model for the amount of hydration product and ion concentration in liquid phase. It is well known that the prediction of C3A hydration is so difficult by using only phase equilibrium model. At that time, it was assumed that C4AH13 can be formed heterogenious, and it was easily generated under the influence of supersaturation state of Ca ions in the vicinity of the C3A particles, so that good agreement between the measured value and the predicted value was obtained.
