Damage analysis and mechanical performance of alkali-activated aggregate concrete composite beams under corrosion condition

Alkali-activated aggregate concrete (AAC), as a low-carbon and environmentally friendly building material, can effectively utilize industrial waste residues and construction waste. However, the optimal replacement ratio of alkali-activated aggregate (AA) and the mechanical performance of AAC structures under corrosive environments remain unclear. This study systematically investigates the effects of the AA replacement ratio (0%, 25%, 50%, 75%, 100%) and the corrosion level (0%, 3%, 5%, 8%, 10%) on the flexural performance of AAC composite beams. First, alkali-activated aggregates were prepared from industrial solid waste materials (Red mud). Then, nine prefabricated composite beams with different AA replacement ratios were manufactured, followed by chloride ion erosion and corrosion tests. Finally, flexural tests were conducted on the corroded composite beams. The experimental results indicated that when the AA replacement ratio is 50%, the hydration product content is the highest and the interfacial transition zone is optimized, leading to a peak ultimate bearing capacity of the composite beam. The ductility first increases and then decreases with increasing aggregate replacement ratio. When the AA replacement ratio exceeds 75%, the failure mode of the composite beam changes from ductile flexural failure to brittle shear failure. When the corrosion level is within 3%, the corrosion-induced expansion and compaction effect slightly enhances the bearing capacity, ductility, and energy dissipation capacity. When the corrosion level exceeds 5%, bond degradation causes a significant decrease in bearing capacity, and both the energy dissipation capacity and ductility of the composite beam are notably reduced. The influence coefficient of alkali-activated aggregate and the influence coefficient of corrosion level were proposed, and a formula for calculating the flexural capacity of corroded AAC composite beams was established. Finally, a refined finite element model of the corroded composite beam was developed. The simulated load–deflection curves and damage distribution verify the accuracy and applicability of the refined numerical model.