Effect of hydroxysodalite on the alkali-activated slag of seawater mixture: Early hydration behavior, chloride binding capacity, and microstructural characteristics

In response to the scarcity of freshwater resources and the high environmental impact of cement production, this research explores the use of seawater to prepare alkali-activated cementitious materials (AAMs). To avoid the adverse effects of high concentrations of Cl − in seawater on performance, the feasibility of synergistic application of hydroxysodalite and seawater in AAMs systems was proposed. By setting the hydroxysodalite content and mixing water type, the effects on the early hydration behavior, Cl − binding capacity, and microstructural characteristics of AAMs were systematically investigated. The results show that hydroxysodalite improves the initial flowability (8 %–14 %) while shortening the setting time (initial setting and final setting are shortened by 32 %–40 % and 26 %–33 %, respectively). Compared with the deionized water mixing system without hydroxysodalite, hydroxysodalite increased the compressive strength of the seawater mixing system by 17.2 %. Seawater causes OH − in hydroxysodalite to migrate out of the β cage, and induces the formation of chlorine-bearing sodalite. At the same time, hydroxysodalite promotes the formation of more C-A-S-H gel, which not only reduces the total porosity but also increases the gel pore ratio. The synergistic effect of these two aspects significantly enhances the chloride ion binding capacity of AAMs. In addition, the binding behavior of AAMs towards Cl − follows the Freundlich model. Overall, the introduction of hydroxysodalite provides an effective strategy for significantly improving the early performance and Cl − binding capacity of AAMs mixed with seawater.