ACI Materials Journal by Dr. Rahel Khalid Ibrahim.
The effect of high temperature on the mechanical properties and microstructure of nanosilica-incorporated mortars has been studied. Results show that the incorporation of nanosilica increases both compressive and flexural strengths significantly at both ambient and after a 2-hour exposure to 752°F (400°C) temperatures; the strengths increase with the increase of nanosilica content. A significant decrease in strength was recorded for all control and nanosilica-incorporated mortar specimens after a 2-hour exposure to 1292°F (700°C) heat; however, nanosilica-incorporated specimens show higher residual strength than those without nanosilica. Microstructural analysis shows that nanosilica reduces the calcium hydroxide crystals to produce more calcium silicate hydrate, the process that contributes to the strength and the residual strength of the material. In addition, the material exhibits a stable structure state up to 842°F (450°C), while exposure to higher temperatures results in a decomposition of hydration products.
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