Influence of Seawater and Salt Ions on the Properties of Calcium Sulfoaluminate Cement

Abstract

Calcium sulfoaluminate (CSA) cement is recognized for its rapid hardening, early strength development, low carbon, and eco-friendly characteristics. The impact of seawater ions on the properties of CSA is studied utilizing varying concentrations of sea salt containing four different ions (K+, Mg2+, SO42−, and Cl−). A comprehensive assessment of CSA-based materials includes mechanical performance, hydration products, and microstructure analysis through bending and compression strength tests, pH tests, X-ray diffraction (XRD), scanning electron microscopy (SEM), digital image correlation (DIC), and acoustic emission (AE) analysis. The study reveals that the addition of seawater enhances the strength of CSA cement-based materials, transitioning their performances from structural brittleness to ductility. It highlights the different impacts of salt ions on CSA mortar: chloride (Cl−) minimally affects strength, but in combination with magnesium (Mg2+), it leads to the encapsulation of ettringite by M-S-H gel, thereby weakening the overall strength of CSA cement. Furthermore, mixing CSA mortar with potassium sulfate (K2SO4) solution enhances early-stage strength (cured<7 days) but diminishes it in the later stages (cured>7 days). A synergistic effect is observed when SO42− and Mg2+ ions coexist, resulting in an overall strength reduction of CSA mortar. Notably, when K+, Mg2+, SO42−, and Cl− are combined in solution, the pH significantly decreases compared to natural seawater, leading to a notable reduction in compressive strength of CSA mortar.