Research on the effect of aggregate characteristics influencing macro-mechanical degradation and meso-damage evolution in coal gangue concrete with freeze-thaw performance

The efficient reutilization of coal gangue (CG) not only mitigates the environmental pollution resulting from its accumulation but also addresses the scarcity of natural aggregate resources. Nevertheless, there is a paucity of comprehensive and in-depth studies examining how variations in aggregate properties influence the mechanical properties of coal gangue concrete (CGC) under the freeze-thaw (F-T) effect and its micro-fracture mechanisms. This paper explores the mechanical performance and damage evolution of concrete prepared with two typical types of CG from China, used as coarse aggregates. The investigation considers different replacement ratios (0, 40%, 70%, 100%) and F-T cycles (0, 25, 50, 75, 100). A multi-scale methodology integrating macro- (mechanical properties of concrete) and micro-scale (NMR, XRD, XRF, SEM) approaches was utilized to systematically assess the performance and evolution of the underlying mechanisms in CGC under F-T effect. A damage model was formulated based on meso-statistical damage theory (MSDT), explicitly incorporating the effects of F-T cycles. It was found that the physical properties and mineral composition of CG significantly affect concrete's mechanical performance. A high quartz content can endow CG aggregates with strong supporting capabilities. CG's stable clay minerals and internal maintenance function can enhance the internal pore structure. An increase in the aggregate replacement ratio results in a marked increase in the concrete's susceptibility to F-T damage. F-T could intensify the deterioration of concrete's internal structure, significantly increasing its initial damage and leading to a marked increase in brittleness following peak stress in specimens.