Instant mechanical recovery of heat-damaged nanosilica-incorporated cement composites under various rehydrations procedures

Abstract

In this work, the instant mechanical recovery and the thermal resistance of nanosilica(NS)-incorporated cement composites were investigated. The composites were exposed to various heating temperatures (200, 500, 800, and 1000 degrees C) and rehydration conditions (25 degrees C/65% RH or water rehydration), and weight, surface morphology, density, compressive strength, and X-ray diffraction were assessed. Si-29 nuclear magnetic resonance was used to analyze the relationship between the mean chain length (MCL) of calcium silicate hydrates (C-S-H) and instant mechanical recovery. Increasing the NS content substantially increased the compressive strength after heating and strength recovery through rehydration at 25 degrees C/65% RH, particularly after exposure at 500 and 800 degrees C. The NS pozzolanic reaction afforded strength recovery and was linearly related to increasing MCL of C-S-H. The pozzolanic reaction produced a compact matrix; therefore, the strength recovered considerably following rehydration in water, even after heating to 800 degrees C, because of the combined effect of hydrate formation and the resistance of the matrix to thermal shock.