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Abstract

The rapid accumulation of waste vehicle tires and the increasing demand for cement pose significant environmental challenges through land pollution and CO2 emissions. The combined use of recycled steel fibers (RSFs) recovered from waste tires and supplementary cementitious materials (SCMs) offers a sustainable solution to these issues. This study investigates concrete incorporating 20% fly ash (FA), varying metakaolin (MK) contents (4–16%), and RSF dosages of 0.5–1.5%. Mechanical properties (compressive, split tensile, and flexural strengths) and durability characteristics (sorptivity, water absorption, chloride permeability, and homogeneity) were evaluated at 7, 28, and 90 days. Results showed that the mixture containing 20% FA and 12% MK exhibited the optimum overall performance among the SCM blends. The incorporation of 1% RSF further enhanced performance, resulting in increases of approximately 44–46% in compressive strength, 41–45% in split tensile strength, and 50–55% in flexural strength compared to the control mix. SEM observations confirmed the formation of a denser and more compact microstructure in the optimized FA–MK blends. Life cycle assessment demonstrated reductions in global warming and water depletion impacts through the combined use of MK and RSF. ANOVA and regression analyses indicated statistically significant effects of MK and RSF on mechanical and durability properties, while response surface analysis identified 12% MK and 1% RSF as the optimum combination within the investigated parameter range.

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