Effect of C─ A─ S─ H─ PCE Nanocomposites on Early Hydration and Performance of Portland Cement at Low Temperatures

Engineers have been working on new technologies to increase the early strength in order to meet the development demands of industrialized construction. In this study, calcium aluminum silicate hydrate (C─ A─ S─ H)–polycarboxylate ether (PCE) nanocomposites with different Al/Si ratios were synthesized by the solution coprecipitation method. The stability and particle size of nano-C─ A─ S─ H were characterized by visual inspection and zeta potential analysis. The effects of the nano-C─ A─ S─ H with different Al/Si ratios on setting time, compressive strength, and hydration heat of cement paste were measured at 10°C. Moreover, the effects of different curing temperatures (−15°C, 0°C, 10°C, and 20°C) on the structure and micromorphology of hydration products were investigated using quantitative X-ray diffraction (QXRD), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) tests. The results show that the particle size increased and the stability of nano-C─ A─ S─ H decreased with the increasing Al/Si ratio. Nano-C─ A─ S─ H promotes the generation of hydration products at different temperatures, refines the volume structure, and improves the early strength of cement, and the most apparent enhancement effect occurs at lower temperature. There is an optimal Al/Si value for promoting cement hydration, beyond which the accelerating effects decrease. Compressive strength improvement of 112.0% and 167.1% were obtained at ages of 16 and 24 h for mortars containing S-0.15 (in which the Al/Si ratio in nano-C─ A─ S─ H was 0.15), compared with that of the reference group at 10°C. In addition, the early-strengthening effects of nano-C─ A─ S─ H at low temperatures was more obvious, making it a more suitable competitor for winter construction.