A major waste product generated during steel production has found use as a wastewater treatment agent. The same slag used to effectively remove phosphorus and other pollutants during municipal wastewater processing can be reused again as a component in concrete manufacture, according to researchers from RMIT University inMagnified images showing concrete made with treated slag (center), conventional aggregates (left) and raw slag (right). The treated slag forms a more seamless bond with the cement paste, making the concrete stronger. Source: Rajeev Roychand et al. Australia.

The slag loses its pollutant adsorption powers over time but in the process is imbued with improved strength and mechanical properties. This post-wastewater treatment material has shown potential to be repurposed again as an ingredient in concrete manufacture.

The researchers tested concrete samples made using treated and untreated slag as a replacement of conventional coarse aggregates at a replacement level of 50 vol% and compared with a control mix containing 100% of conventional coarse aggregates. Experiments demonstrated that concrete made with post-treatment slag was 8% stronger than concrete containing slag obtained directly from a steel mill. The material produced was also 17% stronger than concrete made with traditional aggregates. This was mainly because the post-treatment slag formed a more seamless bond with the cement that acts as a binder within the concrete.

The study published in Resources, Conservation and Recycling points to a useful alternative to landfilling for this abundant industrial byproduct.