Mechanism underlying effects of CaO-MgO combined expansive agent on hydration kinetics of cement-based systems

Abstract

With the order of better understanding the early hydration process and reaction mechanism of CaO-MgO combined expansion agent-involved cement-based systems (CMEA-CBS), CMEA dosage, CaO to MgO ratio (Ca/Mg), MgO activity, hydration temperature, and water-binder ratios (w/b) were chosen as the influencing factor. Accordingly, isothermal calorimetry was implemented to analyze the hydration heat release law, and the Krstulovic–Dabic model was applied to investigate the hydration kinetic. Moreover, the activation energy of CMEA-CBS was calculated. The findings of this study are as follows. The incorporation of CMEA can accelerate the hydration of cementitious systems. Hydration temperature increase markedly promote the hydration reaction of CMEA-CBS. The hydration reaction of CMEA-CBS is a complex associated reaction process dominated by multiple reaction mechanisms in sequence. At both 20 °C and 45 °C, the hydration process of CMEA-involved cement-based systems experienced three stages of crystallization nucleation and crystal growth (NG), phase boundary reaction (I), and diffusion (D), and the hydration mechanism was NG → I → D. However, the hydration of CMEA-CBS at 65 °C switched from the NG stage to the D stage directly. The hydration promotion effect of increasing temperature on I and D process of CMEA-CBS is less than I and D process of pure cement. Compared to the other groups, the temperature increase had the least effect on the early hydration process of 10%-C1M1-M-0.4 with the lowest apparent activation energy.

Keywords:

• cement-based materials
• CaO-MgO combined expansion agent
• hydration kinetics
• activation energy

Authors’ contribution

ZC: Conceptualization, Methodology, Funding acquisition, Project administration, Supervision, Formal analysis, Writing—original draft, Writing—review and editing. JZ: Investigation, Validation, Data curation, Formal analysis, Writing—original draft. CW: Investigation, Resources. BC: Supervision, Validation. MD: Methodology, Resources.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.

Data availability statement

Data will be made available on request.

Additional information

Funding

This research was funded by the Guangxi Science and Technology Major Program (GKAA23023034); Guangxi Natural Science Foundation, China (2022GXNSFFA035035); Guangxi Key Research and Development Program (GKAB22036007); The National Key Research and Development Program of China (2021YFB2600903). The authors are grateful for this support.