A novel shotcrete accelerator prepared from industrial aluminum mud waste and its influence on cement hydration

Abstract

In this study, the aluminum sulfate and industrial aluminum mud solid waste were respectively used to prepare shotcrete accelerators (named as AFA and AFS, respectively). A comparative analysis of their performance was conducted, and the underlying mechanisms were investigated. Different concentrations of sulfuric acid (25 %, 30 %, 35 %, 40 %, 45 % 50 % respectively) and liquid to solid ratios (2:1, 3:1, 4:1, 5:1, 6:1) were employed for the acid leaching of aluminum mud, among which 35 % mass concentration of sulfuric acid and 3:1 of liquid to solid ratio were identified as the optimal conditions according to the setting and hardening performance of cement. AFS exhibited superior effectiveness on enhancing the rapid setting and early age strength in cement pastes and mortars compared to AFA. The working mechanisms of AFA and AFS were revealed via the examination of ionic concentrations and pH values in pore solution, as well as the evolution of hydration heat and hydration products during the hydration process. The results showed that AFS generated higher concentration of Al3+ and SO42- ions during hydration as compared to AFA thus promoted the formation of a larger amount of ettringite. Moreover, the introduction of both AFA and AFS into cement pastes significantly lowered the pH values in pore solution, and AFS was more obviously, which accelerated the cement hydration process. This study presents an innovative approach in utilizing industrial aluminum mud solid waste for the development of a novel accelerator with promising performance characteristics, opening up new opportunities for its wide range of application.