Fan Wang

Local properties of the interfacial transition zone (ITZ) are closely related to damage evolution in concrete, but improvements in interfacial microstructure do not always translate into better overall mechanical performance. This review examines ITZ formation, multiscale characterization, damage evolution, and mechanical response through experimental, numerical, and interface-modification studies. ITZ boundaries and thicknesses depend on characterization parameters and identification criteria; interface quality therefore requires assessment of local properties and their spatial distributions. ITZ effects vary with damage stage and target response. Following preferential interfacial cracking, crack paths, localization, and macroscopic response depend on relative fracture resistance, weak-zone distribution, and loading conditions. The damage-controlling location can consequently shift among the ITZ, mortar, and aggregate, helping explain inconsistent improvements after interface strengthening. Links between measured ITZ properties, post-peak softening, and fracture-energy dissipation still require joint validation against local damage and macroscopic response. Priorities include identifying conditions for damage transfer, determining whether early interfacial cracks continue to contribute, and testing predictions across conditions using local parameters. This synthesis supports evaluation of ITZ contributions, model-parameter selection, and interpretation of interface modification, providing a basis for concrete design and optimization.

Red mud, as a by-product of alkaline regeneration of alumina, has limited application due to its strong alkalinity, fine particle size, and complex composition. In this work, red mud porous ceramics with uniform pore size distribution and high mechanical strength were prepared using a foam-gel casting method. The effects of solid loading and sintering temperature on the microstructure of porous ceramics were systematically investigated. The porosity of red mud-based porousceramics sintered at 1150 °C with a solid content of 60.4% was 33.7%, and the maximum compressive strength was 54.70 MPa, while the porousceramics prepared with a solid loading of 34.1% and sintered at 1050 °C achieved a maximum porosity of 79.7% and a compressive strength of 2.36 MPa. Increasing the solid loading reduced porosity and enhanced compressive strength, allowing for the tailoring of mechanical properties to meet specific application requirements. Higher sintering temperature promoted the formation of the liquid phase, enhanced particle bonding, and further improved the compressive strength. Additionally, toxicity leaching tests confirmed that the ceramics are environmentally safe, with leachate levels well within regulated limits. These results demonstrate the potential of foam-gel casting as an effective route for transforming red mud into value-added porous ceramics, thereby contributing to sustainable waste utilization and broadening the application prospects of red mud-based materials.