Ceramics-Silikáty

Magnesium sulfoaluminate cement (MSAC) is a promising low-carbon binder for marine engineering, yet its performance in authentic seawater environments remains unclear. Here, natural seawater is used as the mixing water to prepare MSAC pastes and is systematically compared with a freshwater system. The hydration behaviour, microstructural development, and macroscopic properties are assessed through the flowability, setting time, compressive and flexural strengths, water resistance, volume stability, and early-age micro-expansion. The hydration products are characterised by X-ray diffraction and scanning electron microscopy. The results show that the seawater mixing has little effect on the workability or setting and does not alter the dominant hydration pathway. The strength is slightly lower than in freshwater; however, the seawater-mixed MSAC still delivers high 28-day performance, achieving ∼14 MPa in flexural strength and ∼80 MPa in compressive strength. The material exhibits good water resistance with a softening coefficient above 0.80 and controlled early micro-expansion. MSAC forms a dense, needle-like 5·1·7 phase framework, which is further filled with an amorphous gel; the microstructure becomes even more compact in seawater. Overall, MSAC maintains stable hydration and favourable mechanical properties in seawater, supporting its potential for sustainable marine engineering applications.