Effect of phase change composites on hydration characteristics of steam-cured cement paste

The application of phase change materials (PCMs) in building materials has attracted more and more attention. However, there is little information on the interactions between PCMs and cementitious material during hydration process. This study investigates the influence of PCMs on cement hydration behavior under steam curing condition. Three kinds of composite phase change material (CPCM) are synthesized, denoted by D/P, EG/P and D/EG/P, respectively. The thermal stability and crystalline phase of PCMs are characterized. The effects of above PCMs on hydration process of cement are evaluated by several testing methods, including isothermal calorimetry, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy. Results indicate that CPCMs exhibit good thermal stability compared with single paraffin when the operating range is less than 200 °C. The time to reach the heat release rate peak of binders containing paraffin, D/P, EG/P and D/EG/P is 20 min, 20 min, 20 min and 30 min earlier than the cement pastes without PCM at 60 °C isothermal condition, respectively. The addition of a small amount of CPCM can accelerate the early hydration of steam-cured cement paste due to the combined action of paraffin and carriers with high surface area that can provide nucleation sites. Moreover, the combination of two carriers promotes cement hydration better than the single carrier. However, the number of hydration products and phase compositions of steam-cured cement paste are almost not affected by the addition of CPCM.