Effects of salinity and temperature on strength of cement-stabilised silt in tropical coastal regions

Cement stabilisation efficacy in tropical coastal regions is critically compromised by high soil salinity and temperatures, yet the underlying synergistic mechanisms remain insufficiently characterised. This study quantitatively investigated the evolution of unconfined compressive strength (qu) and microstructural alterations in cement-stabilised silt under varying pore-water salinities (S0 = 0%–4%) and curing temperatures (5°C, 25°C, 45°C). Mercury intrusion porosimetry revealed that increasing salinity from 0% to 4% reduced micropore porosity by 17.8%–19.4% and increased macropore porosity by 44.9%–46.2% under elevated temperatures, reducing water-retention capacity. Scanning electron microscopy and thermogravimetric analysis indicated that elevated salinity and temperature synergistically enhanced ettringite (AFt) formation and drove a morphological transition, inducing microcracking and pore expansion. Consequently, qu exhibited linear degradation with increasing salinity and temperature. Crucially, high-salinity samples (S0 ≥ 3%) cured at 45°C suffered structural disintegration on immersion, causing a complete loss of strength. This study reveals that the expansive behaviour of AFt crystals induced by salinity–temperature synergy, combined with their physical deterioration of the microstructure driven by osmotic pressure upon water immersion, constitutes the primary mechanism for strength degradation in cement-stabilised silt. These findings reveal appreciable engineering implications for coastal cement stabilisation projects, necessitating durability assessments explicitly accounting for coupled salinity-thermal-wetting conditions.