Microstructure transformation of MCM-41 modified cement paste subjected to thermal load and modelling of its pore size distribution

This study examines the effects of highly reactive, mesoporous MCM-41 silica on the thermal resistance and microstructural stability of Portland cement paste (CP). The motivation is to enhance cement composites (CC) properties using supplementary cementitious materials (SCMs), addressing environmental challenges from global cement production. The research involved modifying CP with 0–2 wt% MCM-41 and subjecting it to thermal loads from 20 °C to 700 °C. Evaluations included compressive and tensile strengths, density, water absorption, and shrinkage. Characterization techniques like X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) analysed phase composition and pore distribution. Results showed that MCM-41 significantly improved compressive strength, with a 26.9 % increase at 0.75 wt% content. Tensile strength also improved up to 33.8 % for 0.25–1 wt% MCM-41 content. Thermal stability tests indicated enhanced performance in the 200–500 °C range by reducing microcrack formation. XRD analysis revealed that MCM-41 influenced the phase composition, particularly delaying the thermal decomposition of portlandite and enhancing the stability of calcium silicate hydrates (CSH). Microstructural analysis revealed a denser, more cohesive cement matrix with reduced water absorption and shrinkage, enhancing durability. Additionally, MIP studies showed that MCM-41 contributed to a finer pore structure, improving the overall mechanical properties despite increased porosity. To supplement the findings, peak models have been tested to assess the ability to numerically predict pore size distribution of thermally loaded CP. Thus, MCM-41 is effective for improving the thermal and mechanical properties of CP, offering potential for applications in thermally stressed environments, contributing to more sustainable construction materials.