Fire resistance of high-volume fly ash mortars with nanosilica addition

High-volume fly ash has been widely used in concrete to reduce the cost and environmental impact of producing cements. However, the effect of high temperature on cement-based materials containing fly ash and nanosilica has not been well characterized. In this study, cement was replaced by high-volume fly ash combined with colloidal nanosilica to produce high strength mortars with high residual strength after exposure to high temperatures of 400 °C and 700 °C. Heated and unheated specimens were subjected to flexural and compression tests. The samples were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) tests; and their porosity were determined using BET (Brunauer, Emmett, and Teller) technique to study the specimens’ behavior after exposure to high temperatures. High strength mortars can be produced using nanosilica and fly ash with resultant high residual strength, as confirmed by the porosity, XRD and TGA tests results.

► High strength mortars were formed using high volume fly ash, cement and nanosilica.
► Results show high residual strength after exposure to high temperature of 700 °C.
► The pore size distribution at nano-scale decreased.
► We conclude a reaction occurs between the silica from the nanosilica and fly ash.
► A new binding material was formed by the dehydration of calcium silicate hydrate.