Multiscale analysis of the properties and failure mechanism of red mud-based geopolymers

With advancements in materials science, geopolymers derived from industrial solid waste, such as red mud (RM), offer a promising alternative to cement-based materials in mine backfilling. Due to its strong alkalinity and heavy metal content, RM has attracted considerable research interest. In this study, RM, ground granulated blast slag (GGBS), fly ash (FA), and coal gangue (CG) were combined to create a novel, low-carbon filling material (RGF + C) with broad environmental applicability. Laboratory experiments were conducted using a simple centroid method and digital image correlation (DIC) to assess the mechanical performance of RGF pastes at varying ratios. Microscopic characterization and numerical simulations were used to analyze internal mechanisms, including synergistic enhancement and crack propagation. Results show that the optimal uniaxial compressive strength (UCS) of 5.25 MPa and bending strength of 2.55 MPa were achieved at a RM:GGBS:FA ratio of 0.366:0.317:0.317. DIC and ABAQUS mesoscopic simulations demonstrated that microcracks initiated and expanded under load, forming a two-dimensional crack network, ultimately leading to failure. This crack evolution closely matched physical test results, confirming the reliability of the simulation approach. Further microstructural analyses (XRD, FTIR, TG-DTG, SEM-EDS) revealed that the interaction among RM, GGBS, and FA significantly enhanced pozzolanic reactions, promoting gel phase formation and improving mechanical properties. These findings underscore the synergistic potential of solid waste-based geopolymer systems and provide insights into the sustainable and efficient utilization of red mud and other industrial by-products in construction materials.