The effect of phase change materials on cement hydrate in steam-cured cement-based materials

The application of phase change materials (PCMs) in steam-cured cement-based materials is very interesting, and a good improvement effect has been achieved in the water resistance of specimens. However, there are few studies on the interaction between PCMs and steam-cured cement-based materials. The influence of PCM, including lauric acid (LA), polyethylene glycol (PEG4000) and paraffin (P-58) on the hydration products of steam-cured cement paste were explored in this study. Calcium laurate is synthesized from lauric acid and calcium hydroxide in atmospheric water medium without additives to facilitate analysis the impact of LA on hydration products. The physical and chemical interactions occurring in the PCMs modified cement pastes were investigated using thermal gravimetric analyzer (TG) and Fourier transform infrared spectrometer (FTIR). The type and morphology of hydration products were studied using X-ray diffraction (XRD), Scanning electron microscope (SEM) and Energy Dispersive Spectroscopy (EDS). The results show that pure calcium laurate is synthesized, and calcium laurate has only low calcium content and free acid. The P-58 evaporates during the thermal decomposition of samples. The addition of P-58 delayed the decomposition of calcium hydroxide. There is no new product formed in the steam-cured cement pastes containing P-58. The addition of LA and PEG4000 into the steam-cured cement pastes promotes the formation of organic salt-carboxylate. The carboxylate can be decomposed into carbonate phase at high temperature. In the current investigated area, the addition of LA, PEG4000 or P-58 has almost no influence on the quantity of cement hydration products and phase compositions of steam-cured cement pastes.