Analysis of fire-resistance improvement mechanism in low-lime calcium silicate cement paste through nanoscale pore-structure analysis via synchrotron X-ray nanoimaging

Abstract

This study investigates the mechanism for enhancing the thermal resistance of a low-lime calcium silicate cement (CSC) and ordinary Portland cement (OPC) blend paste cured in a carbonation environment. The physicochemical changes induced by heating were analyzed by evaluating the compressive strength, surface crack formation, and volume variation after exposure to 200, 400, 600, and 800 °C. X-ray diffraction with Rietveld refinement and thermogravimetric analysis were used to assess qualitative and quantitative changes in the reaction products. Additionally, synchrotron X-ray nanoimaging was employed to analyze the correlation between the structure of the reaction products and thermal resistance. The CSC–OPC blended samples exhibited the highest strength and the least volume reduction after heating compared to the single-blended CSC and OPC samples, indicating improved matrix stability. The enhanced thermal resistance of cement paste incorporating 80 % CSC and 20 % OPC was attributed to the interlocking structure of calcite and vaterite crystals, which helped maintain the matrix integrity after heating.