Experimental Study on Macroscopic and Microscopic Tensile Strength Characteristics of Steel-Fiber-Reinforced Rubber Concrete

This study examined the reported splitting-tensile response of 17 concrete mixtures labeled by nominal rubber replacement levels of 5–20% and steel fibers at 0–1.5% by volume after 7 and 28 days of curing. The reported strength values were considered together with failure photographs, representative load-displacement curves, acoustic-emission (AE) energy records for three selected mixtures, and qualitative scanning electron microscopy (SEM) observations. Rubber addition was associated with lower splitting-tensile strength, whereas several rubber–fiber mixtures recovered or exceeded the ordinary-concrete value. Among the tested combinations, SF1RR5C had the highest reported strength (4.27 MPa at 28 days, 12.4% above the ordinary-concrete value). The load-displacement curves and post-failure photographs indicate delayed separation and residual load capacity in the fiber-containing specimens. The AE and SEM observations provide qualitative, mixture-specific evidence consistent with crack bridging; they do not independently quantify internal damage, porosity, or fiber-matrix bond strength.