Mechanical Properties and Microstructure of Steel Fiber Reinforced Recycled Aggregate Concrete

The weak mechanical behavior of recycled aggregate concrete (RAC) stems from microstructural defects in its composition. This study investigates the reinforcement of RAC through steel fiber incorporation. Using RAC replacement ratios and steel fiber contents as variables, this study examined their effects on compressive strength, splitting tensile strength, elastic modulus, and Poisson’s ratio. The axial compressive stress–strain curves of steel-fiber-reinforced RAC specimens were systematically measured. Scanning electron microscopy was employed to elucidate the modification mechanisms of steel fibers in RAC. The findings indicate that although greater replacement ratios weaken the mechanical performance of steel-fiber-reinforced RAC, an increase in fiber dosage enhances its strength. The most significant enhancement occurs when fiber content increases from 0.5% to 1.0%; at a replacement ratio of 0, the splitting tensile strength achieves the highest improvement of 11.14%. By considering the influencing factors, including the replacement ratio and steel fiber content, mechanical performance indices such as cube compressive strength were determined. Furthermore, the quantitative correlations linking the transformed values of various indices and the governing variables, together with the complete stress–strain curve formulations, were developed. The enhancement in RAC performance can be ascribed to the crack-bridging and crack-resisting effects provided by the embedded steel fibers. This research provides crucial experimental evidence supporting the engineering applications of steel-fiber-reinforced RAC. This study offers essential empirical data that underpin the practical implementation of steel-fiber-enhanced RAC.