Evaluating the role of magnesium aluminate nano spinel in phase composition, meso-porosity, compressive strength, and drying shrinkage of alkali-activated slag

Abstract

The effect of nano magnesium aluminate (MA) spinel on the performance of blast-furnace slag with low NaOH content (3 wt%) was explored for the first time in the present work. Two different temperatures (500 and 800 °C) were applied to prepare nano spinel with different degrees of crystallinity. The impact of nano MA spinel crystallinity and content on phase composition, microstructure, compressive strength, meso-porosity, and drying shrinkage of alkali-activated slag (AAS) was evaluated. The results showed that nano spinel prepared at 500 °C (MA500) reduced the drying shrinkage and increased the compressive strength of AAS significantly, while MA800 showed a lower effect. The activated mixtures containing 0.5 wt% nano spinel demonstrated the highest performance regardless of nano spinel type. Adding nano spinel induced the formation of a hydrotalcite phase and enhanced the incorporation of Al inside calcium silicate hydrate, resulting in a substantial improvement in the performance of AAS. Nano spinel achieved the concept of “sustainability”, which strongly contributes to producing high-performance materials with low carbon footprint by utilizing low sodium hydroxide content.