Determining the efficiency of SCMs in reducing ASR-driven solidification pressure through coupled microstructural analysis and thermodynamic modelling

This study couples advanced thermodynamic modelling and comprehensive experimental validation to quantify the role of fly ash (FA) and calcined clay (CC) in mitigating alkali–silica reaction (ASR)-induced damage. Results from Damage Rating Index, SEM–EDS, XRD, and TGA were critically compared to equilibrium modelling outputs predicting ASR-phase formation and solidification pressures. Thermodynamic predictions, recalibrated using experimentally validated pressure thresholds, precisely correlated with flexural strength and microstructural deterioration, clearly delineating conditions for ASR-induced expansion and cracking. Distinct replacement thresholds for FA (>20%) and CC (>15%) were identified as optimal intervals for ASR mitigation. Differences in alkali-binding capacity and reactivity kinetics between FA and CC critically influenced the formation of ASR crystalline and amorphous phases, effectively suppressing expansion. This approach defines quantitative relationships between SCM-induced changes in pore solution chemistry, ASR phase assemblage, and pressure development, establishing validated thresholds for SCM dosage to limit concrete deterioration.