Properties and effective improvement approaches of basic magnesium sulfate cement under high-temperature pre-curing

Abstract

Basic magnesium sulfate cement (BMSC) cured at room temperature has excellent mechanical properties and is widely used in the production of magnesia-based building materials products. However, BMSC products are often manufactured higher than room temperature. This work examines mechanical properties of BMSC under high-temperature pre-curing (HTPC). Citric acid (CA), selected as additive, content was increased and self-made 5Mg(OH)2·MgSO4·7 H2O seed crystal (517 SC) was added to the BMSC to improve their properties. Compressive strength and water resistance were tested, accompanied with an examination of hydration products, monitoring of electrical conductivity evolution and microstructure analysis. The results suggest that HTPC has negative effects on mechanical properties of BMSC and the main hydration product of the BMSC is transformed from 517 phase to Mg(OH)2. The increase in CA content can improve the mechanical properties of BMSC under HTPC to some extent. The addition of self-made 517 SC can significantly improve the compressive strength and water resistance of BMSC under HTPC, which can be attributed to promoting the in-situ growth of 517 phase without reducing the degree of MgO hydration.