Characterization of high strength mortars with nano alumina at elevated temperatures

•Nano alumina enhanced compressive strength of mortars by 16% at room temperature.•Nano alumina enhanced residual properties of mortars at temperatures up to 400 °C.•1% nano alumina decreased gas permeability of mortars at temperatures up to 600 °C.•Addition of nano alumina lowered the intensity of CH at room temperature and 400 °C.•Addition of nano alumina transformed CH phase from well to ill crystalline.

In this study, the effect of elevated temperatures on chemical composition, microstructure and mechanical properties of high strength mortars with nano alumina was investigated. Mortars with 1, 2 and 3% nano alumina as cement replacement were prepared and then exposed to 100 °C, 200 °C, 300 °C, 400 °C, 600 °C, 800 °C and 1000 °C. XRD, DSC and SEM tests were carried out to identify chemical composition and microstructure changes in the cement matrix after being exposed to elevated temperatures. Residual compressive strength, relative elastic modulus and gas permeability coefficient of samples were also obtained. A brittleness index was defined to monitor changes in brittleness of samples after being exposed to elevated temperatures. Nano alumina enhanced compressive strength of samples up to 16% and improved residual compressive strength. An increase in the relative elastic modulus, higher energy absorption and lower permeability were also observed when 1% nano alumina was added.