Effects of limestone powder on the early hydration of tricalcium aluminate

To further explore the effects of limestone powder (LP) on the hydration of Portland cement as well as the formation and transformation mechanism of calcium carboaluminate phases, the hydration reaction between LP and tricalcium aluminate (C3A) is thoroughly studied in this paper. Due to the crucial influence of gypsum on the hydration of C3A, two systems are well studied, viz. the C3A–LP–H2O and the C3A–LP–CaSO4·2H2O–H2O system. The replacement levels of LP are 0, 5 mass%, 15 mass% and 25 mass% by mass of total binder. The hydration behavior of these two systems are studied using isothermal calorimetry, XRD and quantitative XRD, and chemical shrinkage. The obtained results show that more LP delays the formation of hemicarboaluminate. In the C3A–LP–CaSO4·2H2O–H2O system, the formation of calcium carboaluminate phases only begins after gypsum is consumed. Moreover, LP can reduce the chemical shrinkage resulting from the volume increase of the formation of calcium carboaluminate phases.