Synergistic immobilization of chloride ions by metakaolin and calcined hydrotalcite in basic magnesium sulfate cement

Abstract

Basic magnesium sulfate cement (BMSC) is a promising green building material due to its excellent properties such as high-strength, lightweight, low-solubility and good stability. However, BMSC prepared with magnesia derived from precipitate of brine may inevitably have residual chloride ions (Cl−) leading to a negative impact on its long-term performance and service life. In this work, the effects of metakaolin (MK) and calcined hydrotalcite (cLDH) on the chloride binding capacity (Cb), mechanical performance, porosity and electrochemical impedance of BMSC were systematical investigated. The results reveal that chloride binding capacity of BMSC with MK and cLDH is significantly enhanced with a Cb value of 72.4%. The synergistic mechanism can be described as the structure reconstruction of cLDH by intercalation of Cl− and the strong electrostatic adsorption of the newly formed aluminum magnesium silicate hydrate (M-A-S-H) to Cl−. Moreover, the measured electrochemical impedance spectroscopy (EIS) data of BMSC are well fitted by the equivalent circuit model Rs(Q1(Rct1W1))(Q2(Rct2W2)). Thus, the Cb value of BMSC at curing age of 28 d can be accurately predicted with the measured resistance (Rct1) (1 d) using the fitted linear equation.