High-fidelity data-driven multi-objective design of class F fly ash–geopolymer concrete

Class F fly-ash geopolymers (FA-GPCs) can slash the CO₂ burden of structural concrete, yet their mix design still relies on costly trial-and-error. The first geometry-normalized database of FA-only geopolymer concretes was assembled—799 mixes from 67 publications, every reported strength converted to the 150 Ø 300 mm cylinder equivalent—and interrogate it with a three-scenario, data-availability workflow. Eighteen machine-, deep- and hybrid-learning models are benchmarked; a Voting ensemble predicts 7–28 days compressive strength with an R 2 of 0.962, while an LSTM + XGBoost hybrid forecasts mix-specific CO₂ footprints at an R 2 of 0.996. SHAP analysis reveals that the Si/Al ratio and initial curing temperature dominate early-age strength, whereas total Na₂SiO₃/NaOH and Na₂O/binder ratios control embodied carbon, underscoring an inherent strength–footprint trade-off. These surrogate models feed a multi-objective optimizer (NSGA-II, confirmed superior to NSGA-III and MOEA/D) that explores the 1st–99th-percentile bounds of 11 mix variables. The resulting Pareto fronts deliver eco-efficient recipes reaching 65 MPa at ≤30 kg CO₂/m 3 (at 90-d curing age) and extend to 87 MPa under relaxed carbon targets. Compared with state-of-the-art optimization that rely on mixed precursors or un-normalized data, the proposed pipeline widens the design space, lifts strength by 10–20 MPa and trims CO₂ by up to 70 %. The framework— in this order: data curation, geometry correction, scenario-specific ML, evolutionary optimization—cuts trial batching efforts and offers practitioners ready-to-deploy, class F FA-GPC mixtures while providing a transparent template for other alkali-activated binders which was confirmed by an experimental validation. • Geometry-normalized database of ~800 FA-geopolymer mixes enables apples-to-apples ML. • Voting ensemble predicts 7–28-d strength at R 2 = 0.962; LSTM + XGBoost CO₂ at R 2 = 0.996. • SHAP shows Si/Al ratio and curing-T drive strength, while Na-metrics govern CO₂ footprint. • NSGA-II yields Pareto mixes hitting 65 MPa at ≤30 kg CO₂/m 3 (90-d curing). • Framework cuts trial batches and offers ready-to-use class F FA-GPC recipes.