Reactivity and reaction kinetics of calcium aluminosilicate glasses

Abstract Optimizing the utilization of SCMs in concrete requires understanding their composition-structure–reactivity relationships, a task that remains challenging due to their inherent structural and chemical complexity. This study addresses this challenge by analyzing a diverse range of calcium aluminosilicate (CAS) glasses, serving as pure-phase model systems to better understand SCM reactivity. Sixteen CAS glasses were synthesized, with their amorphous nature confirmed by X-ray diffraction (XRD), and their reactivity assessed using heat release measurements from a modified R 3 test. X-ray diffraction (XRD) was performed to study the glass structure. Although several structural parameters—non-bridging per tetrahedral oxygens (NBO/T), average Q n (Si) species, metal–oxygen bond strength ( S M–O ), the average number of topological constraints per atom ( n r ), and XRD hump maxima angle—correlated linearly with CaO (reflecting its depolymerizing effect), the 72-h heat release followed a non-linear trend with CaO. It increased initially, peaked at around 35–45 mol % CaO, then decreased. Consequently, high-CaO glasses reacted rapidly but did not sustain their reaction over time, whereas those with higher SiO 2 content showed slower yet more prolonged reactivity. These findings demonstrate that reactivity cannot be directly predicted from existing structural descriptors alone.