Experimental study on the deformation characteristics of magnesium potassium phosphate cement paste at early hydration ages

This paper aims to study the deformation characteristics of magnesium potassium phosphate cement (MKPC) pastes at early hydration ages. A jar unit was designed to measure the volume deformation of MKPC samples in balloon, and the volume deformation of MKPC prism specimens was tested with micrometer. Additionally, the hydration temperature of fresh MKPC pastes was measured. The phase compositions and micro-structure of MKPC paste were also analyzed. The results showed that there was a good nonlinear correlation between the volume shrinkage rates of MKPC sample in balloon and MKPC prism specimen from 5-h to 48-h hydration ages. The correlation coefficient (R-2) was 0.991 and the correlation can be mathematically described as y = 2.7645 x (2) - 0.1672x + 0.0027. For calculating the linear volume deformation rate of MKPC pastes with controllable early hydration reaction rate, the length of MKPC prism specimens at 24-h hydration age (L-24h) is suggested as the reference length (L-0) in order to eliminate the early fluctuation of volume deformation. Adding some fly ash in MKPC led to higher peak values of the volume expansion rate and residual volume expansion rate of sample in balloon due to the morphology and activity of fly ash. The volume shrinkage rate of MKPC prism specimen containing 10% fly ash was only 2/3 of that of reference specimen M0 at 28-day hydration age, which was also due to the activity and micro-aggregate effects of fly ash.