Turning Sludge into Strength for a Concrete Revolution in Sustainable Sewers
In a bold step toward cleaner infrastructure and greener construction practices, engineers from the University of South Australia (UniSA) have struck gold—or rather, grey matter. Their latest research tackles an eye-watering $70 billion challenge posed by corroding cement sewer pipes, replacing the traditional material with something both stronger and more sustainable: water treatment sludge.
That’s right. The murky by-product of drinking water purification, once a landfill-bound nuisance, is now being transformed into a concrete alternative that boasts higher strength and improved resistance to corrosion. It’s a fascinating pivot from waste to wonder.
Cement’s Dirty Secret
Cement is the backbone of the construction industry—cheap, readily available, and, structurally speaking, quite reliable. But when it comes to sewage systems, it has a fatal flaw. Acid and microbial corrosion run rampant in these high-moisture, high-bacteria environments, eating away at concrete from the inside out.
According to estimates, Australian taxpayers are footing the bill for up to $70 billion in repairs and maintenance of sewage infrastructure. That’s not just a drop in the bucket—it’s a flood. The need for a more durable, corrosion-resistant material has never been more urgent.
Enter Sludge-Based Concrete
The research, published in the Journal of Building Engineering, highlights the potential of alkali-activated materials (AAMs) to completely change the game. These next-gen concretes swap out cement for industrial by-products like ground granulated blast-furnace slag (GGBS) and—here’s the kicker—alum-based water treatment sludge (AWTS).
PhD candidate Weiwei Duan, who is leading the project, explains: “Sludge is usually disposed of in landfill sites, which not only reduces available land for other uses, but also harms the environment, creating CO₂ emissions from transporting the waste.”
But by integrating this sludge into AAMs, researchers have discovered a concrete that is over 50% stronger than traditional GGBS mixtures, while resisting acid degradation and microbial attack. It’s a win-win for performance and sustainability.
The Science Behind the Sludge
To create the sludge-enhanced mixture, researchers experimented with replacing 20% to 40% of GGBS with AWTS. The result? A serious uptick in compressive strength and durability. Even more impressively, the material limited the penetration of sulphur-oxidising bacteria, notorious culprits in sewer pipe corrosion.
The key lies in the chemistry of the alkali-activation process, which produces a dense, resilient microstructure. These AAMs form a gel-like binder that outperforms traditional cement in harsh sewer environments. Better still, they don’t rely on Portland cement, one of the largest single sources of carbon emissions in the world.
A Circular Economy in Action
Professor Yan Zhuge, principal supervisor on the project, frames the breakthrough as not just a technological step forward, but a circular economy milestone.
“This has the potential to extend the service life of sewage pipes, reduce maintenance costs, and promote the reuse of water treatment by-products, thus contributing to the circular economy,” she says.
By redirecting waste from landfill and reducing reliance on carbon-heavy cement, the research promises to shrink the environmental footprint of infrastructure projects across the board. And with the construction industry still responsible for nearly 40% of global carbon emissions, the stakes are enormous.
National Recognition and a Promising Future
For his efforts, Weiwei Duan was awarded the 2025 Australian Water Association’s Student Water Prize—the first UniSA student to claim the accolade in six decades. It’s a fitting nod to a project that not only breaks new scientific ground but could reshape how countries approach sewer system longevity and environmental stewardship.
The full study, titled “Evaluating microbiologically influenced corrosion in alkali-activated materials incorporating alum sludge”, was co-authored by UniSA’s Professor Yan Zhuge, Dr Yue Liu, Professor Christopher Chow, and Alexandra Keegan from the SA Water Corporation.
Industry Implications and Global Impact
So what does this mean for the construction world at large? In short, a roadmap to more sustainable, cost-effective, and resilient infrastructure. Governments, municipal planners, and engineers now have a scientifically validated alternative to the status quo—one that aligns with both performance targets and climate commitments.
Beyond Australian borders, the potential is just as vast. Cities grappling with crumbling sewer networks and ballooning maintenance budgets could find relief by adopting similar sludge-enhanced materials. With proper policy incentives, the innovation could scale globally, creating a ripple effect of environmental and financial benefits.
What Comes Next?
With Adelaide University set to launch in January 2026—a merger of the University of South Australia and the University of Adelaide—researchers are poised to continue expanding the scope and reach of their discoveries. The combined strengths of both institutions will help accelerate research like Duan’s into mainstream industrial practice.
From smarter material science to practical engineering, the foundation is being laid for a new generation of infrastructure projects that work in harmony with the planet, not against it.
Reinventing the Future of Waste
Turning waste into resource isn’t just a clever trick—it’s the backbone of future-forward thinking in the built environment. And with projects like UniSA’s leading the charge, the future of infrastructure looks stronger, cleaner, and decidedly more circular.
