Hydration characteristics and microstructure development of sodium hydroxide slag pastes exposed under different curing environments

The aim of this research is to investigate the effect of curing environments on strength development and microstructure changes of alkali activated slag pastes (AAS). Mixtures of AAS are prepared using 5% NaOH content at a water to binder ratio of 0.35. Samples are exposed to six different curing environments, including heat treatment in different temperatures (30, 60 and 90 °C) for 2, 7 and 28 days. Their properties, as heat of hydration, compressive strength as well as porosity and morphology have been investigated on both fresh and hardened pastes via XRD, NMR, MIP, TGA and ESEM/EDX. Heat treatment was found to be very effective in promoting high early strength, accelerating the strength development of AAS pastes. Samples cured at 30 °C showed the best results in terms of compressive strength and porosity development. The compressive strength of 28 days samples is slightly reduced as the curing temperature increased. There is no significant difference in the types of hydration products present in the AAS pastes cured at different temperatures for up to 28 days.