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<p>The present study evaluates the coupled influence of curing temperature (27–55&#xa0;°C) and gypsum addition on laboratory synthesised pure M3-alite (C<sub>3</sub>S) phase hydration, linking phase evolution and kinetics with microstructural development and C–S–H polymerization. To carry out the study, alite pastes were prepared and cured at 27&#xa0;°C, 40&#xa0;°C, and 55&#xa0;°C for 28 days, with and without 5% gypsum. The resulting microstructure and phase composition was determined using XRD, TGA, SEM, BSE-EDX, <sup>29</sup>Si-NMR and MIP. XRD analysis showed that hydration increased with temperature, reaching 76.7% at 27&#xa0;°C, 80.1% at 40&#xa0;°C, and 80.4% at 55&#xa0;°C for alite pastes. With 5% gypsum, the degree of hydration was further increased to 79.4% at 27&#xa0;°C, 82.7% at 40&#xa0;°C, and 85% at 55&#xa0;°C. BSE-EDX analysis further demonstrated that Ca/Si ratio of C-S-H gel was lowered with higher temperature and gypsum addition. For alite pastes, Ca/Si ratio was decreased from 1.54 at 27&#xa0;°C to 1.46 at 55&#xa0;°C in the outer C-S-H. At 55&#xa0;°C for alite with 5% gypsum mix, the outer C-S-H displayed the lowest Ca/Si ratio of 1.42, signifying a greater abundance of silica and more stable C-S-H gel. Furthermore, MIP and <sup>29</sup>Si-NMR studies provided further insights into the refinement of the pore structure and molecular-level interactions, confirming the densification of the microstructure with higher porosity and enhanced hydration behaviour at elevated curing temperature. These findings support a new hypothesis that the enhanced hydration of alite at elevated temperatures results from a synergistic interaction between thermally accelerated dissolution kinetics and sulfate-mediated nucleation control. The proposed mechanism integrates temperature-dependent reaction rates with sulfate adsorption effects, offering a unified understanding of microstructural densification and C–S–H polymerization in pure alite systems.</p> Graphical abstract <p></p>

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Effects of elevated curing temperatures on synthesized M3-C3S cement phase with and without gypsum: hardened microstructure and phase composition

  • 期刊论文

  • 发表日期：

    2026年4月22日

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  • Rajesh Kumar,
  • Nagasubramanian Gopalakrishnan,
  • Shashank Bishnoi

摘要

The present study evaluates the coupled influence of curing temperature (27–55 °C) and gypsum addition on laboratory synthesised pure M3-alite (C3S) phase hydration, linking phase evolution and kinetics with microstructural development and C–S–H polymerization. To carry out the study, alite pastes were prepared and cured at 27 °C, 40 °C, and 55 °C for 28 days, with and without 5% gypsum. The resulting microstructure and phase composition was determined using XRD, TGA, SEM, BSE-EDX, 29Si-NMR and MIP. XRD analysis showed that hydration increased with temperature, reaching 76.7% at 27 °C, 80.1% at 40 °C, and 80.4% at 55 °C for alite pastes. With 5% gypsum, the degree of hydration was further increased to 79.4% at 27 °C, 82.7% at 40 °C, and 85% at 55 °C. BSE-EDX analysis further demonstrated that Ca/Si ratio of C-S-H gel was lowered with higher temperature and gypsum addition. For alite pastes, Ca/Si ratio was decreased from 1.54 at 27 °C to 1.46 at 55 °C in the outer C-S-H. At 55 °C for alite with 5% gypsum mix, the outer C-S-H displayed the lowest Ca/Si ratio of 1.42, signifying a greater abundance of silica and more stable C-S-H gel. Furthermore, MIP and 29Si-NMR studies provided further insights into the refinement of the pore structure and molecular-level interactions, confirming the densification of the microstructure with higher porosity and enhanced hydration behaviour at elevated curing temperature. These findings support a new hypothesis that the enhanced hydration of alite at elevated temperatures results from a synergistic interaction between thermally accelerated dissolution kinetics and sulfate-mediated nucleation control. The proposed mechanism integrates temperature-dependent reaction rates with sulfate adsorption effects, offering a unified understanding of microstructural densification and C–S–H polymerization in pure alite systems.

Graphical abstract