Researchers have shown how a by-product of steel making can be used to both treat wastewater and make stronger concrete, in a zero-waste approach to help advance the circular economy.

Produced during the separation of molten steel from impurities, steel slag is often used as a substitute aggregate material for making concrete.Steel slag can also be used to absorb contaminants like phosphate, magnesium, iron, calcium, silica and aluminium in the wastewater treatment process, but loses its effectiveness over time.

Engineering researchers at RMIT University examined whether slag that had been used to treat wastewater could then be recycled as an aggregate material for concrete.The concrete made with post-treatment steel slag was about 17% stronger than concrete made with conventional aggregates, and 8% stronger than raw steel slag.Water engineer Dr Biplob Pramanik said the study was the first to investigate potential applications for “sewage-enhanced” slag in construction material.