Effects of nano-silica sol on post-fire performance of concrete

Nano-silica sol (NSS), a colloidal nano-silica aqueous liquid, could better improve the performances of cement-based materials than the relatively widely-used nano-silica powder, but up to now the reported findings had been obtained from tests carried out at normal ambient temperature without exposing to elevated temperatures. To reveal the effects and influence mechanisms of NSS on post-fire performance, a two-staged investigation program encompassing measurement of workability, residual mass ratio (RMR), compressive and flexural residual strength ratio (RSR), wet packing density (WPD), powder X-ray diffraction (XRD) patterns, scanning electronic microscope (SEM) micrographs and pore condition after subjecting to elevated temperatures has been carried out. It was proven that the elevated temperature proliferated connected cracks and surface spalling of NSS concrete. The presence of NSS increased the RMR, slightly lowered the compressive RSR, and had little effect on the flexural RSR. These effects on post-fire performance were explained with respect to the particle packing density, XRD patterns, microstructural characteristics and pore condition including pore size distribution, cumulative pore volume and large pore ratio. • Post-fire performance and influence mechanism of nano-silica sol (NSS) are studied. • Workability, residual mass ratio (RMR) and residual strength ratio (RSR) are tested. • Elevated temperature is found to proliferate connected cracks and surface spalling. • NSS increases RMR, slightly lowers compressive RSR and little affects flexural RSR. • Influence mechanism is revealed via packing, X-ray diffraction and microstructure.