Comparison of the alkali-silica reactions of ferronickel slag aggregate in fly ash geopolymer and cement mortars

Abstract

The use of reactive aggregates in ordinary Portland cement (OPC) concrete is limited due to the potential expansion of alkali-silica reaction (ASR). This study evaluates the ASR expansion of ferronickel slag (FNS) fine aggregate in fly ash geopolymer mortar by the accelerated mortar bar test (AMBT) method. While FNS was found to be reactive in OPC mortar, it was found non-reactive with fly ash geopolymer. The OPC mortar showed extensive expansion and strength reduction after exposure to AMBT condition, whereas the geopolymer specimens showed low expansion and strength increment. Scanning electron microscopy (SEM) images of the OPC mortar specimens after AMBT showed the presence of some ASR gel around aggregate surface. However, a relatively firm bonding was observed between aggregate and binder in the geopolymer mortar specimens. The EDS results showed that the aluminosilicate consumed free alkali in geopolymer binder matrix that reduced the ASR of FNS aggregate in geopolymer mortar.