Concrete, widely used in construction, is a major source of greenhouse gas emissions and resource depletion due to its reliance on cement and NCA. This study evaluates the combined effects of fully replacing NCA with RCA, partially substituting cement with SF, and incorporating NWF on concrete’s engineering performance, durability, and environmental footprint. A three-way ANOVA confirmed highly significant main effects of RCA, SF, and NWF on CS ( p < 10^{− 9}) and STS ( p < 10^{− 8}); 100% RCA reduces mean CS from 76 to 61 MPa, while the synergistic addition of 10% SF and 0.25% NWF recovers 9 MPa of strength. Durability tests reveal that 100% RCA increases water absorption by 25%, but that SF–NWF combinations reduce this penalty by up to 0.48%. CIP doubles under RCA (13–26 mm) yet decreases by 7 mm with SF–NWF synergy, and sulfuric-acid mass loss rises by 3% with RCA but is lowered by 0.6% when additives are applied. A cradle-to-gate life cycle assessment using SimaPro 9.5.0.2 with Ecoinvent 3.10 and the TRACI method shows RCA alone reduces ODP by 18%, GWP by 6.6%, ACP by 8%, and EP by 10%; coupling with 10% SF and 0.1% NWF amplifies these reductions to 25%, 15.7%, 13%, and 16.5%, respectively. Heatmap and sensitivity analyses consistently identify 10SF-100RCA, 10SF0.1N100RCA, and 10SF0.25N100RCA as optimal mixes for balanced performance and sustainability.

The increasing demand for concrete, coupled with the depletion of natural aggregates, has accelerated the use of recycled coarse aggregates (RCA). However, the high porosity of RCA adversely affects mechanical performance. This study develops an integrated experimental and interpretable machine learning framework to improve and predict the mechanical properties of hybrid fiber-reinforced recycled aggregate concrete. Hybrid glass/polyvinyl alcohol fibers (0.05–0.15 % by volume, 10–20 mm) were incorporated into ternary binder systems (OPC/FA/GGBS) with 0 %, 50 %, and 100 % RCA replacement. Elastic modulus (EM) and axial compressive strength (ACS) were measured from laboratory specimens, while predictive models were trained on datasets comprising 302 EM samples and 201 ACS samples, drawn from both experiments and the literature. An artificial intelligence framework incorporating six machine learning (ML) models was optimized using Bayesian optimization with Gaussian Process and Random Forest surrogates and interpreted through SHapley Additive exPlanations (SHAP). Experimental results indicate that 0.1 % hybrid fibers increased EM by 36.96 % and ACS by 38 % at full RCA replacement. Among the models, CatBoost-BO-RF achieved the highest predictive accuracy, with R ² values of 0.9783 for EM and 0.9751 for ACS in training, while maintaining values above 0.90 during validation. SHAP analysis identified fiber length (14.2 %), RCA content (14 %), and water absorption (10.6 %) as dominant factors for EM, whereas WARA (19.9 %), NFA (15.2 %), and Wa (14.1 %) governed ACS. The results confirm that hybrid fiber incorporation significantly enhances mechanical performance and that interpretable ML provides a robust basis for the design and prediction of sustainable RCA-concrete.

The large consumption of natural resources by the construction industry and resultant pollution have inspired the necessity to investigate the potential of eco-friendly materials, such as recycled aggregates and recycled fibers. In this study, the effect of different percentages of recycled coarse aggregate (RCA) and nylon waste fibers (NWF) was investigated on engineering performance and performance-related carbon emissions of high-performance concrete (HPC). Engineering performance indices include compressive strength (CS), splitting tensile strength (STS), water absorption (WA), and chloride ion penetration (CIP). The environmental impact of designed mixes was evaluated using a cradle-to-gate life cycle assessment approach on the HPC mixes. The results showed that the incorporation of 0.25–0.5% yielded maximum STS for all percentages of RCA. The use of NWF helped overcome the negative impact of RCA on the STS of HPC. The use of the 0.1–0.25% volume of NWF was helpful to the permeability-related durability of HPC. CS-related emissions were minimum for concrete incorporating 0.1–0.25% NWF with 0% and 50% substitution levels of RCA, while STS-related emissions were lowest for HPC incorporating 0.5% NWF with 50% and 100% substitution levels of RCA.

Building demolition waste has a significant Environmental impact (EI) including waste generation, CO₂ emissions and land use alteration. Recycling and reutilizing these materials possess the potential to alleviate the strain on landfills and diminish the dependence on natural resources. Recycled concrete aggregates (RCA) from demolished structures were used in producing concrete masonry blocks (CMBs). The mechanical characteristics of the CMB were evaluated and life cycle assessment (LCA) calculations were conducted to assess the environmental implications of the materials employed in the manufacturing process of CMB. Incorporating 25% RCA into CMB resulted in a 1.8% decrease in compressive strength (CS). Subsequently, as the RCA content increased to 50%, 75%, and 100%, CS exhibited a consistent decreasing pattern, with reductions of 2.9%, 10.9%, and 16.4%, respectively. Ultrasonic pulse velocity (UPV) results showed a replicating trend in the CS. Substituting RCA with natural aggregates reduced carbon emissions by 10% but high volumes of RCA were ineffective in reducing emissions due to their adverse impact on CS. When comparing the EI of coarse aggregates only, RCA shows 84% less impact than natural coarse aggregates.