Preparation and Hydration Mechanism of Al-F Complex Alkali-Free Accelerator by Waste Acid of Titanium Dioxide

Abstract

The objective of this study is to prepare Al-F complex alkali-free accelerator from waste acid of titanium dioxide and to evaluate the hydration mechanism of F-ion complex. Setting time, stability, pH value, 1d compressive strength, 28d ratio of compressive strength and SEM were performed on cement pastes produced with an alkali-free accelerator (aluminum sulfate solution containing F-ion). Results showed that the addition of F-ion could form β -AlF3•3H2O complex, which improved the content of Al3+ ion and the stability of the system. The Al-F complex alkali-free accelerator contributed to the rapid formation of ettringite with network structure, as well as to a faster rate of cement dissolution and hydration. Moreover, a conceptual hydration model for pastes containing F-ion alkali-free accelerator was proposed. F-ion was beneficial to destroy the covering effect of C-H-S gel and form a continuous hydration. According to the results, variations in cement different setting time and mechanical strength caused by different concentration of F-ion in the alkali free accelerator are explained.