ASR potential of nickel slag fine aggregate in blast furnace slag-fly ash geopolymer and Portland cement mortars

Abstract

Utilizing nickel slag as aggregates in concrete production proposes an economic option for recycling this industrial by-product, and meanwhile preserves the natural rock aggregate resources. Thus, there is an urgent need to further explore the potentially alkali-silica reaction (ASR) nature. This study investigates the ASR of high-magnesium nickel slag (HMNS) fine aggregate in the fly ash-blast furnace slag geopolymer and Portland cement (PC) mortars. No obvious ASR product is observed in the mortars with HMNS fine aggregate, which exhibit lower ASR expansion than the mortars with ASR reactive sand. In the geopolymer mortars, the reactive Al species initially dissolved from HMNS promote the formation of aluminum-containing alkalis silicate gel layer covered on the surface of HMNS grains. This provides a diffuse barrier to protect the inner silica against further attack of alkalis, and consequently mitigates the deleterious ASR. In the PC mortars, the pozzolanic reaction of HMNS improves the consumption of portlandite in the pore solution to reduce the alkalinity and calcium content, resulting in a suppression to the ASR degradation. The accelerated mortar bar test shows that HMNS is reliable for the utilization without deleterious ASR expansion risk.