Performance of fly ash-based geopolymer incorporated with high magnesium nickel slag: Effects of different cooling conditions

Abstract

High magnesium nickel slag (HMNS), as industrial by-product generated from the pyrometallurgical extraction of nickel, has the great potential to be used as the silica-rich precursor for the production of geopolymers. This work investigated the compressive strength and autogenous shrinkage of fly ash-based geopolymers incorporating HMNS with different cooling conditions. The results showed that HMNS additions could enhance the compressive strengths, while the autogenous shrinkage rates were also increased. The addition of air cooling HMNS with finer particle size could compact the pore structure. Larger proportion of medium-capillary pores formed in the binders raised the capillary pore pressure. Compared with the air cooling HMNS, the water quenching HMNS exhibited relatively higher reactivity. The Ca2+ and Mg2+ ions released from HMNS increased the surface tension of pore solution, resulting in a larger pore pressure developed in the binder. Furthermore, Mg/Si and Ca/Si ratios of binder gel phase were enhanced simultaneously, suggesting that HMNS addition facilitated the development of magnesium/calcium modified sodium aluminosilicate hydrate (N–(M)–A–S–H and N–(C)–A–S–H) gel phases.