The properties and hydration of a calcined coal series metakaolin-limestone-Portland cement system

To enhance the application of coal series kaolinite clay in the cement industry, the properties and hydration of ternary system based on calcined coal series metakaolin (CMK), limestone (LS), and Portland cement were investigated in this work. The results showed that the kaolinite phase transformed into an amorphous phase for coal series kaolinite clay calcined over a wide temperature range. The negative effects of the CMK on the early (3 and 7d) compressive strength of mortars and of LS on the later (28 and 90 d) compressive strength of mortars could be offset by using a combination of LS and the CMK. The combined incorporation of the CMK and LS promoted the hydration of cement at an early hydration age, and the pozzolanic reaction of the CMK generated additional hydration products. In the ternary system, the use of LS weakened the influence of the calcination temperature of the CMK on the early hydration of cement; similar heat release and strength development can be observed for all CMK-LS content blends. At a late hydration age, the incorporation of LS resulted in the formation of carboaluminate instead of monosulfoaluminate, and the CMK enhanced this reaction. As a result, the hydration of Portland cement, CMK, and LS was improved due to the synergistic effect of the CMK and LS, and the mixture of CMK and LS is expected to be a promising supplementary material.