Uncovering the mechanism controlling strength and microstructural evolution of belite-rich cement-based materials at different temperatures

Abstract

The effect of temperature on the properties of belite-rich cement-based (BRC) materials is different from that on Portland cement (PC). This study provides a comprehensive understanding of the mechanisms controlling strength and microstructural evolution at different temperatures, especially C-S-H characteristics, of BRC materials. Phase assemblage, pore structure, and microscopic morphology of BRC paste, as well as phase composition and structure, chemically bound water, and bulk density of C-S-H were investigated using X-ray diffraction (XRD), thermogravimetric analysis (TGA), ¹H and ²⁹Si nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). The strength of BRC mortar increased with temperature is because of the higher hydration degree of β-C₂S, lower porosity (except for 60 °C), and increased main chain length (MCL) of C-S-H. Hydration degrees of 28-d β-C₂S and C₃S increased by 202.5 % and 16.3 %, respectively, while MCL increased by 39.4 % from 5 to 60 °C. The higher temperature sensitivity of β-C₂S is due to its activation energy being 12.4 % greater than that of C₃S in BRC paste. Additionally, gel porosity decreased with temperature due to decreased bound water content and increased 16.7 % bulk density of C-S-H from 5 to 60 °C. Finally, the CaO/SiO₂ was inversely proportional to MCL and bulk density, but positively to H₂O/SiO₂. The findings deepen the mechanistic understandings of the hydration kinetics and microstructural evolution for temperature-affected BRC material.