Influence of graphite tailings with variable activation treatment on the frost resistance of ultra-high performance concrete

To investigate the feasibility of applying graphite tailings (GT) in the production of high-durability ultra-high-performance concrete (UHPC) and its potential application in cold regions, this study systematically investigates the effects of mechanical activation (grinding for 0.5–1.5 h) and chemical activation (modulus of 1.2–1.6) on the freeze-thaw resistance of GT modified UHPC. Through freeze-thaw cycle tests and COMSOL multiphysics numerical simulations, the influence mechanisms of different activation methods on the microstructural evolution and freeze-thaw damage behavior of UHPC were elucidated. The results demonstrate that mechanical grinding for 1.5 h significantly reduces GT particle size, optimizes gradation, and enhances UHPC compactness. Meanwhile, chemical activators with a modulus of 1.4 promote GT participation in hydration reactions, facilitating the formation of C-S-H/C-A-S-H gel networks and refining the UHPC microstructure. Both activation methods effectively mitigate mass loss, relative dynamic elastic modulus degradation, and compressive strength reduction of UHPC, thereby improving its freeze-thaw resistance. Numerical simulations further confirm that activated GT can suppress internal frost-induced stress concentration and enhance the stability of the interfacial transition zone (ITZ) in UHPC. This research provides novel insights into the high-value utilization of GT resources and the design of frost-resistant UHPC.