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Recycling breakthrough unites steelmaking, wastewater treatment and construction sector

Australia’s RMIT University has discovered that steel slag used to treat wastewater can be recycled as an aggregate material for concrete. Researchers also say the recycled material is notably stronger.

Steel slag is frequently used as a substitute aggregate material for making concrete. The material also absorbs contaminants such as phosphate, magnesium, iron, calcium, silica and aluminium during the wastewater treatment process ‘but loses its effectiveness over time,’ says water engineer Dr Biplob Pramanik, based in Melbourne.

Pramanik estimates that the global steelmaking industry produces over 130 million tonnes of steel slag every year. ‘A lot of this by-product already goes into concrete but we’re missing the opportunity to wring out the full benefits of this material,’ he notes.

A perfect match

‘Making stronger concrete could be as simple as enhancing the steel slag by first using it to treat our wastewater,’ the team at RMIT suggests. This thought inspired them to successfully develop a ‘zero waste’ recycling method for the by-product of steelmaking.

They report that concrete made with post-treatment steel slag is about 32% stronger compared to raw steel slag, and roughly 8% stronger than concrete made with conventional coarse aggregates.

‘The things we want to remove from water are actually beneficial when it comes to concrete, so it’s a perfect match,’ Pramanik points out.  

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