Think of a big infrastructure system you’d like to keep running smoothly and sewage emerges near the top of the list. Unfortunately, concrete corrosion and fatbergs plague sewage systems around the world, leading to costly and disruptive maintenance.
Fatbergs are gross globs of congealed fat, grease, oil and non-biodegradable junk like wet wipes and nappies that clog sewers. Some grow to be 200 metres long and weigh tonnes.
The presence of fatbergs and general corrosion over time costs billions in repairs and replacement pipes.
Now, engineers at RMIT University, Melbourne, have developed concrete that can withstand the corrosive acidic environment found in sewage pipes, while greatly reducing residual lime that leaches out, contributing to fatbergs. Their findings are published in Resources, Conservation & Recycling.
The RMIT team, led by Rajeev Roychand, created concrete that eliminates free lime – a chemical compound that promotes corrosion and fatbergs.
“The world’s concrete sewage pipes have suffered durability issues for too long,” says Roychan.
“Until now, there was a large research gap in developing eco-friendly material to protect sewers from corrosion and fatbergs.
“But we’ve created concrete that’s protective, strong and environmental – the perfect trio.”
By-products of the manufacturing industry are key ingredients of the cement-less concrete – a zero cement composite of nano-silica, fly-ash, slag and hydrated lime. The new concrete uses large volumes of these industrial by-products, supporting a circular economy, and it surpasses sewage pipe strength standards set by ASTM International.
“Though ordinary Portland cement is widely used in the fast-paced construction industry, it poses long-term durability issues in some of its applications,” Roychand says.
“We found making concrete out of this composite blend – rather than cement – significantly improved longevity.”
Replacing underground concrete pipes is an onerous task. Excavation in urban areas is expensive and often has a ripple effect of prolonged traffic delays and neighbourhood nuisances. The Water Services Association of Australia estimates maintaining sewage networks costs $15 million each year, and billions worldwide.
But the environmental cost is greater – ordinary Portland cement accounts for about 5% of the world’s greenhouse gas emissions. The RMIT study proves that certain by-products can replace cement and are able to withstand the high acidity of sewage pipes.
“Our zero-cement concrete achieves multiple benefits: it’s environmentally friendly, reduces concrete corrosion by 96% and totally eliminates residual lime that is instrumental in the formation of fatbergs,” says Roychand.
Roychand adds that the zero-cement concrete could be made totally resistant to acid corrosion with further development. His team is looking to collaborate with manufacturers and government to develop more applications for the product.
Ian Connellan is a journalist and editor for the Royal Institution of Australia.
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