The potential of ‘sewage-enhanced’ slag

It may not be much to look at, but this image could illustrate a potential win-win if Australian researchers are on the money.

On the left is a magnified view of concrete made from conventional aggregates, while on the right is concrete made, as is increasingly the case, with raw slag – a by-product of steel making.

In the centre is concrete made using treated slag which, the team from RMIT University says, forms a more seamless bond with the cement paste, creating a stronger concrete.

The key to all of this is that the treated slag has already been of use. It became “treated” while absorbing contaminants such as phosphate, magnesium, iron, calcium, silica and aluminium in a wastewater treatment process.

It lost its effectiveness over time, but water engineer Biplob Pramanik and colleagues found it could be recycled.

In a paper in the journal Resources, Conservation and Recycling, they say concrete made with post-treatment steel slag was about 17% stronger than concrete made with conventional aggregates, and 8% stronger than with raw steel slag.

They found that the chemical properties of the slag are enhanced through the wastewater treatment, so it performed better when used in concrete. 

“The things that we want to remove from water are actually beneficial when it comes to concrete, so it’s a perfect match,” Pramanik says.

He stresses, however, that there are still technical challenges to overcome. An important next step is to investigate the long-term mechanical and durability properties of enhanced slag.