Effect of composite alkali activator proportion on macroscopic and microscopic properties of gangue cemented rockfill: Experiments and molecular dynamic modelling

• Optimal composite alkali activator proportion of 1:2 enhances 3-day compressive strength by 31.25% in gangue cemented rockfill. • The activator proportion strengthens the pozzolanic effect of gangue and inhibits calcium hydroxide agglomeration, leading to a denser microstructure. • Molecular dynamics reveals that 12% sodium substitution in C–S–H improves interlayer adhesion and stress transfer. • The proposed alkali-activated gangue method offers a low-cost, sustainable approach for solid waste recycling and reduced cement consumption.