Mechanical properties, microstructure and GEP-based modeling of basalt fiber reinforced lightweight high-strength concrete containing SCMs

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The pressing need to address recent global climate changes calls for replacing high-carbon-emitting cement with environmentally friendly materials that retain the strength and properties of conventional concrete. This study explored the mechanical properties of lightweight concrete (LWC) incorporating shale aggregate and basalt fibers alongside a partial replacement of environmentally detrimental cement with pozzolanic materials like fly ash (FA), blast furnace slag (BS), and silica fume (SF) up to 30 %. Twenty mix designs were developed to examine their mechanical properties and microstructural characterization. It was also observed that SF outperformed other industrial byproducts and gave better strength with the optimum replacement of 20 % cement, achieving 102.6 %, 105.6 % and 109.5 % of the control mix compressive, flexural, and split-tensile strength, respectively. However, a further increase of up to 30 % decreased strength. FA and BS resulted in lower strength than the control sample and other byproducts-based mixes, with compressive strength decreasing by 4 %–20.5 % at replacement levels of 10 %–30 %, respectively. BS resulted in an initial increase in strength at 10 % replacement but decreased by 10.8 %–21.6 % at higher levels. This trend was similar for flexural and tensile strengths. However, adding basalt fibers resulted in higher strength compared to non-fiber mixes and increased the strength of LWC by up to 25.2 %. The micromorphology and pore structure study indicated that the high-performance paste and fibers bridging effect were crucial for high strength. Gene expression programming (GEP) based modeling, validated against our own experimental results, was employed to predict the outcomes, demonstrating strong correlation coefficients for compressive, flexural and tensile strength (0.9430, 0.9609 and 0.9353, respectively). Additionally, SHapely Additive exPlanations (SHAP) analysis was used to assess the impact of each input parameter, highlighting the positive effects of the water-to-binder ratio and lightweight aggregate on the LWC's mechanical properties. This study is novel in its comprehensive examination of the combined impact of SCMs, shale aggregate and basalt fibers on the performance of LWC, a synergy not extensively explored in prior research. Furthermore, a novel generalized constitutive model was developed, and a SHAP analysis was performed to help design an efficient mix design to enhance the mechanical performance of LWC.