Experimental and molecular dynamics insights into the degradation mechanism of alkali-activated cementitious grouting material under compound erosion

Alkali-activated cementitious (AACM) grouting material is a promising grouting material due to its abundant raw material sources and superior low-carbon characteristics. However, the microstructure of the AACM grouting material is significantly affected by ion erosion in marine and saline soils, which impacts the reliability and safety of engineering structures. In order to offer feasible insights for developing high-durability grouting materials, this study examines the degradation mechanism of an AACM grouting material when exposed to chloride-sulfate-magnesium erosion environments. Results indicate that the 112 days of chloride-sulfate-magnesium compound erosion resulted in a decrease of mass and compressive strength for AACM grouting material were 1% and 26%, respectively. Magnesium salt erosion led to dealumination and decalcification of C-(A)-S-H, as well as the decomposition of hydrotalcite and the formation of M-S-H and gypsum. Chloride salt decreased the amounts of gypsum, and the sulfate salts alleviated the formation of Friedel’s salt. Molecular dynamics simulations reveal that the electrostatic interaction between Mg and [SiO 4 ] 4- was stronger than that between Ca 2+ and [SiO 4 ] 4- , with SO 4 2- exhibiting a greater adsorption effect on Ca 2+ compared to Cl - . Na + hindered the diffusion of SO 4 2- and Cl - , reducing kinetic energy release in the system. In contrast, the diffusion of SO 4 2- and Cl - was facilitated by Mg 2+ , which weakened the adsorption efficiency of C-(A)-S-H. The matrix strength was decreased by the disruption of the total kinetic energy balance in the C-(A)-S-H solid-liquid system. The results emphasize the need to optimize the Al/Si ratio to enhance the durability of grouting materials.