Inhibitory Mechanism of an Aluminophosphate Phase Change Material on Early Hydration of Cement

In this investigation, in order to reveal the effects of the lab-prepared aluminophosphate phase change material (PCM P-Al ) on early hydration of cement, the solubility of PCM P-Al in water and NaOH solution simulating cement paste alkalinity, was determined, and the influences of PCM P-Al on hydration kinetics of fresh cement paste were characterized. Besides, hydration products of cement incorporated with different dosages of PCM P-Al were also identified based on thermogravimetric analysis (TGA), and microscopic morphologies of cement particles at different hydration times were characterized. Results showed that PCM P-Al incorporation significantly reduced cement hydration heat flow, accumulated heat, and 24h calcium hydroxide content. Solubility and microscopic morphology results indicated that flocs were formed during the hydration induction period under the alkaline conditions of cement paste when PCM P-Al was added, and that a greater quantity of flocs were generated as the PCM P-Al dosage increased. The flocs not only adhered to surface of the cement particles, inhibiting cement minerals, especially tricalcium silicate, from undergoing further hydration, but also trapped free water in the floc network. As a result, the early hydration of cement at acceleration stage was significantly inhibited, and the inhibitory effects became more obvious with increasing PCM P-Al dosages.