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Aging infrastructure and rising sewerage temperatures pose increasing risks for corrosion of concrete sewerage pipes around the world. Failing pipes are a significant threat to utility operations, public health and the environment. However, there could soon be a solution. Professor in Structural Engineering at the University of South Australia STEM, Yan Zhuge, is leading a project focused on a self-healing concrete that could help prevent future pipelines from corroding.

Over the past five years, Prof Zhuge has attracted more than $4 million worth of grants and published 149 journal papers. In 2018 she won the South Australian Innovation Award in Engineering for her research on using waste in concrete.

Prof Zhuge’s latest project is focused on developing a self-healing concrete that can be used in sewage pipes. The project is being partially funded by a $501,504 Australian Research Council grant and involves researchers from the University of South Australia and University of Queensland.

Prof Zhuge said this technology could transform the pipeline industry and Australian utility operations.

“The idea of self-healing concrete is not new. It has been around for five or six years,” Prof Zhuge said.

“The problem was that it wasn’t suitable for sewage pipes. Our idea uses a product that is more suitable for sewage pipes.”

Corrosive acid from sulphur-oxidising bacteria in wastewater, along with excessive loads, internal pressure and temperature fluctuations are cracking pipes and reducing their lifespan. Surface coating is a common method for fixing deteriorating concrete, however, it is labour intensive and costly. Another issue is that it is temporary – 20 per cent of repairs fail after five years and 55 per cent fail after ten.

In 2018, SA Water approached the University of South Australia to find a way to prevent the exorbitant amount of sludge at drinking water treatment facilities across its network from going to landfill. During tests conducted by Prof Zhuge and her team, they found that the water treatment sludge was resistant to corrosion due to its high aluminium content.

This led to Prof Zhuge researching a way in which microcapsules composed of water treatment sludge and calcium hydroxide powder could be embedded into concrete during the mixing process, counteracting the corrosive effect of wastewater on concrete pipes.

“Sludge waste shows promise to mitigate microbial corrosion in concrete sewer pipes because it works as a healing agent to resist acid corrosion and heal the cracks,” Prof Zhuge said.

Prof Zhuge said the idea of selfhealing concrete with microcapsules is straightforward.

“During crack propagation, the shell of microcapsules is triggered for release of the healing agents, activating a healing process.

“The amorphous SiO2 and Al2O3 in sludge can react with calcium hydroxide in the presence of water to form solid gel (precipitated from water) to fill the cracks. The carbonation of calcium hydroxide can cause the formation of solid CaCO3 to fill the cracks as well,” Prof Zhuge said.

Challenges along the way

Prof Zhuge said the challenge is in finding the right material for the shell. If the material is too soft, it might break during the concrete mixing process. If the material is too hard, it may not rupture when self-healing is required.

“Most studies have focused on using the mechanical force to trigger the shell to release the healing agent, but as failure modes with microbially induced corrosion (MIC) are sensitive to pH change, our composites are designed with pH sensitive shells.

“The material we selected exhibits an inert behaviour in an alkaline environment (high pH values), but is able to degrade in dilute aqueous acid solution,” Prof Zhuge said. The exact name of the material for the shell remains confidential.

The project is ongoing, with testing still needed to explore the potential of the technology. Prof Zhuge said the methodology is aiming for “early detection and early fix”.

“We still don’t know how wide a crack could be repaired as we haven’t done any testing yet. I don’t think it could close the crack wider than 0.5 1mm or even less,” Prof Zhuge said.

 

A sustainable solution

Unfortunately this self-healing technology only applies to new pipelines and can’t be used for existing aging pipelines. However, while the current methods are costly and only temporary fixes, self-healing concrete could be implemented as a long-term sustainable solution.

Many Australian utilities have pledged to reach net zero emissions by 2050. In order to achieve this target along with interim targets laid out over the next few decades, the industry must shift to a circular economy.

Prof Zhuge said self-healing concrete could help support this transition by providing a new market to use recycled sludge.

“Mainland Australia alone has about 400 drinking water treatment plants, with a single site generating up to 2,000t of treated water sludge annually. Most of that is disposed of in landfill, costing more than $6 million each year, as well as causing severe environmental issues,” Prof Zhuge said.

Disposing a single tonne of sludge in landfill releases approximately 29.4t of carbon dioxide emissions, much higher than cement production.

“This technology will not only extend the lifetime of concrete structures, saving the Australian economy more than $1 billion, but it will promote a circular economy as well by reusing sludge that would normally end up in landfill,” Prof Zhuge said.

Prof Zhuge said she hopes that the project will encourage Australia’s pipeline industry to be more welcoming of new ideas. As for the utility industry, more companies should consider adopting net zero targets. By working closely with researchers like Prof Zhuge and her team, utilities can use research and development to discover more sustainable, circular solutions.

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