Quantitative characterization of nano-scale pore structures in a consistent volume of cement paste subjected to heating via synchrotron X-ray nanoimaging

Although the mechanism of pore formation in cement paste owing to high temperatures is a critical characteristic directly linked to fire resistance, research regarding the 3D characteristics of nano-scale pores within a consistent volume is limited. This study uses synchrotron X-ray nanoimaging to investigate the impact of heating at various temperatures (400, 600, and 800 °C) on the morphology, distribution, and volume changes of nano-scale pores in a consistent volume of ordinary Portland cement paste. The mechanical and hydration properties were assessed via compressive strength tests, X-ray diffraction, and thermogravimetry. After heating to 400 °C, new high-flatness pores formed, whereas heating to 600 and 800 °C resulted in pore coalescence and the formation blade-like pores developed around unhydrated cement particles. Elongated pores formed after heating to 600 °C, which resulted from the decomposition of Ca(OH)₂, leading to the structure being prone to internal cracking.