Properties of alkali activated slag mortar after exposure to elevated temperatures for different time

This paper presents the research on the influence of elevated temperatures and durations on mechanical properties and microstructure of alkali activated slag mortar. Results show that the compressive and flexural strength of specimens deteriorated with the increase of temperature, especially at 800 °C, the flexural strength was lost totally. The increasing duration time had negative effect on the residual flexural strength of specimens after thermal treatment. Meanwhile, X-ray diffraction, scanning electron microscopy and energy dispersive spectrometer were used to further investigate the crystal transformation and microstructural damage in the mortar after submitted to elevated temperatures. After 800 °C thermal treatment, the XRD pattern showed strong diffraction peaks of crystalline phase “Gehlenite“ and the peaks of C-S-H gels disappeared. The obtained SEM/EDS results indicated that the decomposition process of alkali activated slag mortar is responsible for the deterioration of mechanical properties after exposure to elevated temperatures with different duration times.