Preparation of alkali free liquid accelerator for shotcrete with fluorosilicic acid waste liquid and its accelerating mechanism

Abstract

At present, the waste liquid of fluorosilicic acid produced by phosphate fertilizer plants in China creates serious problems of resource waste and environmental pollution. In view of this, a kind of alkali free liquid accelerator (FSA-AF) for shotcrete was prepared herein by using fluorosilicic acid waste liquid, which can realize the purpose of resource utilization and clean production. After testing the performance of FSA-AF, it was found that the addition of FSA-AF greatly shortened the setting time of cement paste, and it had no significant negative influence on early and late compressive strengths of mortar specimens. The results confirmed that FSA-AF was an alkali free liquid accelerator with excellent coagulation promoting property. Moreover, in order to elucidate the accelerating mechanism of FSA-AF, the early hydration process of cement paste, C3A paste and C3S paste with FSA-AF was measured by isothermal calorimetry, and the phase composition and micro morphology of their hydration products were investigated thoroughly by XRD and SEM analyses. Based on these results, the early hydration models of C3A and C3S in the presence of FSA-AF were proposed.