Evolution and improvement of concrete containing manufactured sand under erosion condition

This study investigates degradation mechanisms and improvement strategies for concrete incorporating manufactured granite sand under cyclic drying, sodium sulphate immersion, and freeze-thaw cycles. Three cementitious systems were compared: pure cement (G1), cement–fly ash–slag (G2), and cement–fly ash–slag–nanomaterial (G3). Evaluations included mechanical properties, durability, and microstructural analysis. Results showed G1 exhibited inferior dynamic performance, microcrack propagation, and high chloride permeability, and while G2 enhanced sulphate resistance via pozzolanic reactions, its mechanical improvements were limited. The G3 system demonstrated superior performance, achieving approximately 20% higher compressive strength, over 10% increased dynamic elastic modulus, and 40% reduced chloride permeability. Microstructural analysis revealed that carbon nanotubes and nano-CaCO₃ refined hydration products through filling and nucleation effects, effectively suppressing microcracks and delaying degradation. This research provides guidance for developing high-quality manufactured sand concrete resistant to multi-environmental conditions.