Experimental Study on the Optimal Mix Proportion of Steel Fiber-Reinforced Concrete in Cold Regions

To determine the optimal mix proportion of steel fiber-reinforced concrete in cold regions, this study adopted a multi-factor orthogonal experimental design method. A series of mix proportion schemes was formulated based on different water-to-binder ratios, steel fiber volume fractions, and combinations of mineral admixtures such as silica fume. Mechanical performance tests and freeze–thaw cycle tests were conducted to obtain the strength, deformation characteristics, and durability degradation patterns of specimens with different mix proportions before and after freeze–thaw exposure. Meanwhile, scanning electron microscopy (SEM) was employed to observe the microscopic surface morphology of specimens, both pre- and post-freeze–thaw cycles, and to analyze the damage evolution in pore structures and the fiber–matrix interfacial transition zone, thereby elucidating the microscopic mechanism of freeze–thaw damage. Ultimately, by comprehensively comparing the macro-mechanical properties, freeze–thaw durability, and microstructural characteristics, the experimental results of different groups were evaluated to identify the optimal mix proportion for steel fiber-reinforced concrete, which exhibits excellent mechanical performance and durability under freeze–thaw conditions. The results indicated that freeze–thaw cycles significantly reduced the mechanical properties of the concrete. The optimal mix proportion was achieved with a water-to-binder ratio of 0.4, a silica fume content of 10%, and a steel fiber volume fraction of 1.5%. This optimal mix proportion can provide a direct reference for the material design and application of steel fiber-reinforced concrete in engineering projects located in cold regions.