Australian engineers found that mixing abandoned water-treated sludge with industrial slag would produce more than 50% more concrete alternatives than traditional materials used in wastewater infrastructure.
New alkali-activated materials resist satiating acid bacteria, spending nearly $70 billion a year on Australian taxpayers for repairs and maintenance. This development could change how cities build sewage systems while addressing increasingly serious waste disposal issues.
The study, published in the Journal of Construction Engineering, shows how alum-based water-treated sludge (AWTS) can be combined with ground sandstone furnace stoves to create quality building materials for corrosive environments.
Hidden enemies in sewage systems
Concrete sewage pipes will face ruthless biological attacks. The bacteria that remove sulfate in the wastewater produce hydrogen sulfide gas, which raises hydrogen sulfide into the headspace of the pipe and reduces the surface pH of the concrete below 12. Once this happens, once this happens, sulfur oxidizing bacteria settle the surface and produce sulfuric acid, creating a destructive cycle of consumption through the wall of the tube.
This microbiologically impacted corrosion process (MIC) process produces gypsum – a pasty, non-viscosity material that lacks structural integrity. The formation of gypsum and Ettringites results in large volume expansion within the cement matrix, resulting in rupture and structural failure, requiring expensive repairs in Australia’s 9,300 km of wastewater infrastructure.
“The sludge is usually disposed of in landfills, which not only reduces land for other purposes, but also damages the environment, creating a CO emission from transport waste,” explained Weiwei Duan, a PhD candidate at the University of South Australia.
Engineering Biodefense
The team tested their new material using live sulfur oxidized bacteria from actual wastewater treatment plants. They created controlled laboratory conditions that mimic real sewer environments, including pH changes and bacterial growth patterns found in functional sewage systems.
The key innovation lies in the material composition. By replacing 20-40% of blast furnace slag with processed water treatment sludge, the researchers created alkali-activated materials with fundamentally different chemical properties:
- Reduced calcium availability – Restrict raw material bacteria need to form destructive gypsum
- Lower porosity – Create physical barriers to prevent bacterial penetration
- Hybrid gel formation – Open cash and Nash gels to enhance acid resistance
The science behind superior power
The study reveals a complex chemical defense mechanism. Traditional concrete relies heavily on calcium-rich phases that bacteria can easily attack. New materials create a dual gel system where calcium-based cash gels provide early strength, while alumina silicate-hydrate (NASH) gels contribute long-term durability by reducing solubility in an acidic environment.
Compared with traditional jet furnace slag concrete, samples containing 20-40% water-treated sludge maintained a compressive strength of more than 50% after 56 days of exposure to bacterial attack. Equally important, they show a significant reduction in the formation of destructive gypsum sediments.
The researchers used sophisticated analytical techniques, including X-ray diffraction, infrared spectroscopy, and electron microscopy, to accurately understand how bacterial attacks progress. They found that the improved material produced a “sandwich” structure during corrosion, with a protective silicon dioxide layer with slow acid penetration.
Break the bacterial attack mode
Perhaps most importantly, this study reveals why some materials are better resistant to bacterial damage than others. Using energy dispersion spectroscopy, the researchers found that high concentrations of phosphorus (a key indicator of bacterial activity) were found in phosphorus-corroded samples. This suggests that sulfur-oxidized bacteria can penetrate the protective layer and continue to produce acid directly with the concrete matrix.
However, materials with a water-treated sludge content of 20-40% showed lower porosity, effectively limiting bacterial migration. The reduced calcium content also means that gypsum forms less raw materials, thus disrupting the destructive cycle that usually accelerates pipeline deterioration.
The optimal composition seems to balance several factors: enough calcium is used for early strength development, enough aluminosilicate content for long-term durability, and controlled porosity can prevent bacterial penetration without compromising structural integrity.
Environmental and economic interests
Professor Yan Zhuge, who oversees the study, highlighted the broader implications: “This has the potential to contribute to the circular economy by extending the service life of sewage pipes, reducing maintenance costs, and promoting the reuse of water treatment by-products. The construction industry is one of the largest greenhouse gas emitters in the world, so we can lower the heart and thus reduce the heart.
The environmental benefits range is beyond the range of carbon reduction. Water treatment facilities around the world produce millions of tons of aluminum-rich sludge each year. Current disposal methods often involve landfills, which consume valuable land resources and generate transportation-related emissions.
The study showed that water-treated sludge at 800°C for two hours optimized its reactivity to concrete production. This heat treatment decomposes the hydrated phase and creates a reactive amorphous aluminosilicate phase, thereby enhancing the performance of the final material.
Practical Application
Despite the encouraging laboratory results, the researchers acknowledge the challenges of expanding production. Water treatment sludge, unified pretreatment process and validation of consistent quality control remains an important next step.
The work has been recognized – Duan recently won the 2025 Australian Water Association Student Water Award, the first time a University of South Australia students have received this national honor in 60 years.
With the world working on the stress of aging infrastructure and installation environments, solutions that address waste disposal and infrastructure durability can be invaluable. Research shows that sometimes the answer to complex engineering challenges lies in developing completely new materials, but in searching for innovative uses of waste streams we already produce.
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