Experimental and Machine Learning Based Evaluation of Sustainable Self Compacting Concrete Reinforced with Recycled Steel Wire and Crumb Rubber from End-of-Life Tyres

This study investigates sustainable self-compacting concrete (SCC) incorporating untreated and heat-treated crumb rubber (CR) from waste tyres and tyre-derived steel wire (SW). CR replaced fine aggregate at 5–15%, while SW was added at 1% by volume. Untreated CR reduced workability and strength due to its hydrophobic nature, weak rubber–cement interfacial transition zone (ITZ), and increased porosity. Consequently, 28-day compressive strength decreased from 35.36 MPa to 28.75 MPa, while slump flow declined from 690 mm to 520 mm at 15% CR. Heat treatment improved rubber surface roughness and rubber–cement adhesion, reducing interfacial voids and restoring compressive strength to approximately 35 MPa at lower replacement levels. It also improved workability, achieving a slump flow of 645 mm at 5% CR. The addition of SW enhanced flexural and tensile performance through crack bridging and delayed crack propagation, achieving flexural strength of 6.1 MPa and split tensile strength near 4.0 MPa. Treated CR and SW also reduced chloride permeability and sorptivity by promoting a denser microstructure. Among 567 observations, Support Vector Regression (SVR) provided the best prediction (R2 ≈0.56). The results confirm the potential of treated CR–SW SCC for durable and sustainable construction.