Accumulating vast amounts of pollutants drives modern civilization toward sustainable development. Construction waste is one of the prominent issues impeding progress toward net-zero. Pollutants must be utilized in constructing civil engineering structures for a green ecosystem. On the other hand, large-scale production of industrial steel fibers (ISFs) causes significant damage to the goal of a sustainable environment. Recycled steel fibers (RSFs) from waste tires have been suggested to replace ISFs. This research critically examines RSF’s application in the mechanical properties’ improvement of concrete and mortar. A statistical analysis of dimensional parameters of RSFs, their properties, and their use in manufacturing various cement-based composites are given. Furthermore, comparative assessments are carried out among the improvements in compressive, split tensile, and flexural strengths of plain and RSF-incorporated concrete and mortar. In addition, the optimum contents of RSF for each strength property are also discussed. The influence of RSFs parameters on various strength properties of concrete and mortars is discussed. The possible applications of RSF for various civil engineering structures are reviewed. The limitations and errors noticed in previous review papers are also outlined. It is found that the maximum enhancement in compressive strength (CS), split tensile strength (STS), and flexure strength (FS) are 78%, 149%, and 157%, respectively, with the addition of RSF into concrete. RSF increased cement mortars’ CS, STS, and FS by 46%, 50.6%, and 69%, respectively. The current study encourages the building sector to use RSFs for sustainable concrete.

The effect of combining filler (carbon black) and fibrous materials (steel fiber and polypropylene fiber) with various sizes of coarse particles on the post-cracking behavior of conductive concrete was investigated in this study. Steel fibers (SF) and carbon black (CB) were added as monophasic, diphasic, and triphasic materials in the concrete to enhance the conductive properties of reinforced concrete. Polypropylene fiber (PP) was also added to steel fiber and carbon to improve the post-cracking behavior of concrete beams. This research mainly focused on the effects of macro fibers on toughness parameters and energy absorption capacity, as well as enhancing the self-sensing of multiple cracks and post-cracking behavior. Fractional changes in resistance and crack opening displacement (COD-FCR) and the relationship of load-deflection-FCR with different coarse aggregates of (5–10 mm and 15–20 mm) sizes were investigated, and the law of resistance signal changes with single and multiple cracking through load-time-FCR curves was explored. Results indicated that the smaller size coarse aggregates (5–10 mm) showed higher compressive strength: up to 8.3% and 14.83% with diphasic (SF + CB), respectively. The flexural strength of PC-10 increased 22.60 and 51.2%, respectively, with and without fibers, compared to PC-20. The diphasic and triphasic conductive material with the smaller size of aggregates (5–10 mm) increased the FCR values up to 38.95% and 42.21%, respectively, as compared to those of greater size coarse aggregates (15–20 mm). The hybrid uses of fibrous and filler materials improved post-cracking behavior as well as the self-sensing ability of reinforced concrete.

This paper focuses on the bonding performance of the interface between fiber-reinforced polymer (FRP) profiles and concrete. The bond shear capacity and the bond shear strength of the wet-bond (WB) interface, the shear-key (SK) interface, and the shear-key combined with wet-bond (SK-WB) interface were investigated via double-lap push shear tests with 15 specimens. Varying numbers of shear keys were adopted in the SK and SK-WB specimens to study the influence of the bonding area of the shear keys. The slip between the FRP profiles and the concrete was measured, and the bond stresses at different points of the test zone were calculated with differential operations. The results show that the average bond strength and the maximum slip of the SK-WB interface are significantly higher than those of the SK interface, whereas the average bond strength and maximum slip of the SK interface are significantly higher than those of the WB interface. A much greater concentration of stress was discovered in the SK interface compared with the SK-WB interface. The capacity load value and the maximum slip value of the double-SK interface are higher than those same values of the single-SK interface. The comparison of bond strength was performed between the FRP profiles-concrete interface and the FRP plate-concrete interface. The results show that the bond strength of the WB interface between the concrete and the FRP profile by the double-lap push shear method is much lower than the bond strength of the WB interface between the concrete and the FRP plate when using the double-lap pull shear method. Finally, the significant difference in the bond strengths is explained using the stress analysis method.