Hydration characteristics and mechanism analysis of calcium sulphoaluminate cement mixed with calcareous sand powder in different water environments

Using calcium sulphoaluminate cement (CSAC), calcareous sand powder (CSP), seawater for island infrastructure reduces carbon emissions and mitigates conflicts over construction resources. This study investigated the macro-micro properties of CSAC mixed CSP (CSAC-CSP) in freshwater and seawater environments. The hydration characteristics, mechanical properties, phase composition, microstructural characteristics of CSAC-CSP were analyzed based on electrochemical impedance spectroscopy (EIS), compressive strength , thermogravimetry (TG), X-ray diffraction (XRD), 27 Al Nuclear magnetic resonance (NMR) and scanning electron microscopy-energy dispersive X-Ray spectroscopy (SEM-EDS) tests. Results showed that long-term immersion in freshwater and seawater induces the increase or phase change of hydration products , which in turn enhanced the resistivity and strength of CSAC-CSP. The compressive strength of CSAC-CSP in a seawater environment was higher than in a freshwater environment . The substitution of CSP caused the compressive strength of CSAC-CSP to decrease. Freshwater immersion increased the monosulfate content in CSAC-CSP, whereas seawater exposure resulted in higher ettringite content. The incorporation of CSP promoted the formation of both monosulfate and ettringite . The content of ettringite and amorphous aluminum hydroxide (AH 3 ) was higher in seawater than in freshwater. The adsorption of SO 4 2- and Ca 2+ by the CSP particles could result in a denser interfacial transition zone between the CSP particle and matrix in the seawater environment than in freshwater. Furthermore, using CSAC, CSP and seawater together in the constructing island reefs could provide enhanced environmental benefits. • An island building material with low carbon and seawater corrosion resistant was developed. • Seawater immersion induced more ettringite formation compared to freshwater. • The adsorption of SO 4 2- and Ca 2+ by calcareous sand particle caused a denser microstructure. • The synergistic mechanism among the components was revealed.