Conventional concrete is a common building material that is often ridden with cracks due to its low tensile strength. Moreover, it has relatively low shear strength and, unless reinforced, undergoes brittle failure under tension and shear. Thus, concrete must be adequately reinforced to prevent brittle tensile and shear failures. Steel fibres are commonly used for this purpose, which can partially or fully replace traditional steel reinforcement. The strength properties and bond characteristics between reinforcing steel fibres and the concrete matrix are crucial in ensuring the effective performance of the composite material. In particular, the quality of the bond has a significant impact on crack development, crack spacing, and crack width, among other parameters. Hence, the proper application of steel fibre-reinforced concrete (SFRC) requires a thorough understanding of the factors influencing its bond behaviour and strength properties. This paper offers a comprehensive review of the main factors controlling the bond behaviour between concrete and steel fibres in SFRC. In particular, we focus on the effects of the physical and mechanical properties of steel fibres (e.g., geometry, inclination angle, embedded length, diameter, and tensile strength) on the bond behaviour. We find that the addition of up to 2% of steel fibres into concrete mixtures can significantly enhance the compressive strength, tensile strength, and flexural strength of concrete components (by about 20%, 143%, and 167%, respectively). Furthermore, a significant enhancement in the pull-out performance of the concrete is observed with the addition of steel fibres at various dosages and geometries.

The use of recycled tire rubber, particularly crumb rubber (CR), as a partial fine aggregate replacement offers a sustainable pathway to reduce environmental waste and conserve natural resources, aligning with SDG 9 and SDG 12. This review synthesizes 84 peer-reviewed studies to evaluate the mechanical performance, durability, microstructural characteristics, and practical applicability of crumb rubber concrete (CRC). While CRC typically shows reductions in compressive, tensile, and flexural strengths, stemming from weak ITZ bonding, low stiffness, and increased porosity. It exhibits improved ductility, freeze–thaw resistance, and chemical durability. Empirical polynomial regression models are introduced to quantify strength degradation as a function of CR content, and benchmarking against major design codes indicates that CR levels up to 20 % can satisfy minimum strength requirements for selected exposure classes. Recent enhancement strategies, including RF-RC systems and matrix modifications using sulfate-resistant cement, silica fume, and fly ash, demonstrate quantifiable gains, such as ∼25 % increases in compressive strength, post-crack residual strength improvements from 0.10 MPa to 1.4–3.1 MPa, and ductility enhancements exceeding 70 %. Environmental assessments further show that CRC and multi-waste composite systems can reduce embodied energy by 153–227 MJ/m ³ and CO ₂ emissions by 30–135 kg/m ³ , with LCA studies reporting up to 75 % decreases in total environmental impacts. Field-scale investigations confirm CRC’s feasibility, with composite slabs achieving 10–19 % higher peak loads and 17–33 % higher first-crack loads than conventional concrete. Overall, limiting CR content to 10–20 % and employing performance-based mix optimization are recommended to balance mechanical performance, durability, and sustainability in next-generation low-carbon construction.