Change in microstructure and compressive strength of alkali-activated slag paste at temperature exposure of 50°C

This paper presents a study on the evolution of strength and alteration microstructure of alkali-activated slag (AAS) pastes exposed to 50°C. Ground granulated blast furnace slag (GGBFS) was used as the starting material to prepare slags pastes which were then activated with a range of activators. The preliminary results from the study of these pastes are presented. It was found that all the pastes show a significantly strength loss after exposure to 50°C for 24 hours. This is independent on the activators used. The paste samples were further examined by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM) and sorptivity tests. A hypothesis for strength loss is proposed based on the observations in change of microstructure. This hypothesis will be further validated by the study of the AAS pastes prepared by using phosphorus slags.