Pre- and post-fire behavior of cement and geopolymer concrete with nanomaterials: A comprehensive review

This review aims to evaluate the pre- and post-fire performance of nanomaterial-modified cement concrete and geopolymer concrete, with an emphasis on understanding temperature-dependent behavior, degradation mechanisms, and residual performance. An extensive review of published experimental studies was conducted, focusing on the influence of various nanomaterials on concrete subjected to elevated temperatures. The analysis considers key factors reported in the literature, including nanomaterial type and dosage, binder chemistry, microstructural evolution, moisture condition, exposure temperature, and cooling regime. Cement-based concrete shows limited effectiveness at critical temperatures due to calcium silicate hydrate decomposition, whereas geopolymer concrete exhibits superior inherent thermal stability, with nano-silica representing the most consistent benefits. Carbon-based nanomaterials primarily improve crack resistance and spalling control rather than compressive strength retention under elevated temperature exposure. NM, such as NS and NA, generally improve compressive strength retention by approximately 10–30% compared to control mixes at temperatures up to 300–400 °C, primarily due to pore refinement and vapor-assisted hydration. Beyond 600 °C, the rapid dehydration and decomposition of C–S–H phases result in a substantial loss of strength, often exceeding 50–70%, regardless of NM incorporation. CNT and GO show limited improvement in compressive strength retention but reduce crack width and spalling severity by enhancing crack-bridging and stress redistribution, particularly in the 400–800 °C range. GPC exhibits superior inherent fire resistance, with several studies reporting stable or increased compressive strength up to 300–400 °C and residual strength retention exceeding 60–80% at 600–800 °C, depending on precursor composition and curing conditions. The incorporation of NS further enhances gel densification and structural integrity, leading to consistently higher post-fire performance compared to unmodified geopolymer systems.