Thermo-Mechano-Chemo Dynamics of Clay’s Reactivity and its Correlation with Limestone Calcined Clay Cement (LC³) Performance

Abstract

This study aimed to enhance calcined clay reactivity via mechanical or chemical treatments. Properties were analyzed using XRF, TGA, and XRD; reactivity was assessed with modified Chappelle and R³-bound water tests. XRD patterns for thermally (Th) and thermo-mechanically (ThM) treated clays were similar. Zeolite formation in thermo-chemically (ThC) treated clay was observed and confirmed by TGA with significant mass loss below 400°C. The reactivity of calcined clay exceeded that of untreated clay, in the order Th > ThM > ThC, as confirmed by tests. Subsequently, LC³ mortar was formulated using these activated clays. Assessments included heat of hydration and compressive strength over 90 days, along with XRD and TGA characterizations. The findings demonstrated that the trends in heat of hydration and compressive strength paralleled those observed in reactivity, with LC³-Th > LC³-ThM > LC³-ThC. Although the cement mortar had higher compressive strength than LC³ at 7 days, LC³ showed greater strength after 28 days. A correlation matrix and heat map were also created to analyze the relationship between reactivity and strength. Normalized values confirmed the findings, showing a strong correlation between the R³-bound water value, heat of hydration, and strength up to 90 days.