Potential alkali silica reaction expansion mitigation of ferronickel slag aggregate by fly ash

This study investigates the potential alkali silica reaction (ASR) of ferronickel slag (FNS) aggregate, which is a by-product of nickel production. A class F fly ash was used as a possible ASR mitigation in accelerated mortar bar test (AMBT) specimens containing 50% FNS. There were visible surface cracks on the specimens using no fly ash or 10% fly ash. Use of 20% fly ash reduced expansion by 45% as compared to that with 10% fly ash. In accordance with the expansion limits of Australian Standard, the mixtures using 20 and 30% fly ash were categorized as slowly reactive and nonreactive, respectively. Thermogravimetric analysis (TGA) and microstructural observations confirmed the effectiveness of fly ash in reducing Portlandite content that reduced the ASR expansion. Therefore, the use of 20-30% fly ash as cement replacement is considered as an adequate ASR mitigating measure of FNS fine aggregate.