Green optimization of vapour-cured geopolymer mortars: Predicting cost, mechanical properties, and environmental impact with artificial neural networks

In this study, prediction and optimization of Na concentration, Ms modulus (total ratio of SiO₂/Na₂O in alkali activators), fly ash (FA) and granulated blast furnace slag (GGBFS) contents of geopolymer mortars produced by vapour curing in a prefabricated element production plant were carried out focusing on compressive strength, cost and environmental impacts. After the compressive strengths of geopolymer mortars made with comprehensive mixture designs were obtained experimentally, an artificial neural network (ANN) model was developed to estimate the compressive strength from Na, Ms, FA and GGBFS input variables. Moreover, primary energy (PE), global warming potential (GWP, equivalent-CO₂ emission) and cost were optimized separately in different compressive strength ranges with ANN predictions. The efficiency optimizations were also performed to evaluate the cost and environmental impacts per unit compressive strength. As a result of the optimizations, the maximum compressive strength of geopolymer mortar coded with 0.41 FA/0.59 GGBFS (Na = 6.75, Ms = 0.83) was determined as 54.42 MPa. The most efficient geopolymer mortar mixtures within the optimization ranges were 0.29 FA/0.71 GGBFS (Na = 3, Ms = 0.25, 27.79 MPa) regarding GWP with 1.82 (kgCO₂/m³)/MPa, 0.34 FA/0.66 GGBFS (Na = 3, Ms = 0.55, 31.49 MPa) regarding PE with 27 (MJ/m³)/MPa, and 0.38 FA/0.62 GGBFS (Na = 6.56, Ms = 0.66, 52.50 MPa) considering cost efficiency with 2.29 (€/m³)/MPa. FA + GGBFS based geopolymer mortars stand out as the most sustainable options in terms of energy efficiency and carbon footprint with lower PE/MPa and GWP/MPa values compared to 100 %FA and 100 %GGBFS based geopolymer mortars. Optimized geopolymer mortars are 78 %, 35 %, and 42 % more efficient than traditional OPC based mortars in terms of CO₂ emissions, energy consumption, and cost, respectively.