Synergistic effect of recovering hardened cement powder and aluminum sulfate alkali-free liquid accelerator for enhancing the hydration and hardening of cement paste

The hardened cement powder (HCP) produced by the concrete waste disposal process can have a significant impact on the environment. How to effectively use HCP is the focus of current researchers. In this work, the synergistic effect of the treated hardened cement powder (T-HCP) and accelerator (ASS) was studied. The synergistic mechanism was studied by apparent porosity, hydration heat, XRD and SEM. Results demonstrated that the T-HCP can be used together with aluminum sulfate alkali-free liquid accelerator to improve the strength of cement. The main reason is T-HCP contains cement clinker mineral phase and fine CaCO3 crystals, in which the clinker mineral phase can be rehydrated, and the fine CaCO3 crystals can be used as nucleation sites to accelerate the generation of hydration products. Besides, adding T-HCP can improve the performance of cement mortar and save cost considering the economic aspects.