Understanding Mix Design Trends in Fly Ash-based Geopolymer Concrete through Multi-study Data Analysis

Abstract

Fly ash-based geopolymer concrete is increasingly investigated as an alternative to ordinary Portland cement concrete, but published mix designs vary substantially in precursor composition, alkaline activator formulation, aggregate proportions, curing conditions and reported strength. This study quantitatively examined prevailing practices using a literature-derived database containing 252 mixtures from 32 published studies. Descriptive statistics and frequency analyses were used to characterise binder composition, constituent dosages, activator characteristics, curing conditions and 28-day compressive strength, while Pearson correlation analysis assessed linear relationships among the principal variables. Of the mixtures analysed, 83 used fly ash as the sole binder and 169 incorporated at least one supplementary binder. Fly ash content ranged from 180 to 500 kg/m³, and compressive strength ranged from 7.0 to 79.7 MPa, with a mean of 34.8 MPa. Sodium silicate dosage and sodium hydroxide dosage exhibited the strongest positive correlations with compressive strength, with coefficients of 0.65 and 0.63, respectively. The sodium silicate-to-sodium hydroxide ratio showed a moderate negative correlation of −0.59, whereas curing temperature had a moderate positive correlation of 0.37. Most remaining relationships were weak to moderate, indicating that strength development cannot be explained adequately by a single mix-design variable. The findings demonstrate considerable heterogeneity in reported formulations and provide a quantitative benchmark for future development of more consistent, data-driven mix-design and reporting practices for fly ash-based geopolymer concrete.