Temperature‐Dependent Hydration and Microstructural Evolution of β‐C 2 S‐Rich Pastes With Metakaolin, Quartz, and Gypsum

The present study investigates curing‐temperature effects on hydration and microstructural evolution of metakaolin‐rich calcined kaolinitic clay (MK), quartz powder (Q), and gypsum induced belite binders. A β‐Dicalcium silicate (β‐C 2 S)‐rich powder was synthesized using Boric acid (H 3 BO 3 ) as a polymorph stabilizer, followed by blending with either MK or Q‐rich reference filler, together with 5 wt% gypsum, and cured at 27°C, 40°C and 55°C at a water‐to‐binder ratio of 0.40. Hydration kinetics, phase assemblage, hydrate structure, and pore structure were characterized using isothermal calorimetry, quantitative X‐ray diffraction (QXRD), thermogravimetric analysis/differential thermogravimetry (TGA–DTG), 29 Si and 27 Al magic‐angle spinning nuclear magnetic resonance (MAS NMR), scanning electron microscopy with backscattered electron imaging and energy‐dispersive X‐ray spectroscopy (SEM/BSE–EDX) and mercury intrusion porosimetry (MIP). It was inferred that elevated curing temperature strongly accelerated early heat evolution. XRD‐Rietveld revealed that at 28 day—degree of hydration (DoH) was only 31.4% at 55°C, whereas the quartz blend's hydration increased up to 82.3% at 55°C. NMR study showed that higher curing temperature and MK addition yielded a more polymerized Calcium‐Alumino‐Silicate‐Hydrate (C–(A)–S–H) gel (higher mean chain length (MCL)). SEM–EDX showed that for MK induced mixes, the microstructure evolved as a denser but more heterogeneous assemblage at 55°C. Overall, these findings show that curing‐temperature effects depend strongly on blend chemistry and require performance‐based validation.