Soon, cracking in some 117,000 kilometres of sewer pipes in Australia could be prevented via the use of water treatment sludge. This would not require any human intervention and could help save AU$ 1.4 billion in annual maintenance costs. A first-of-its-kind project, led by Professor Yan Zhuge a sustainable engineering expert at the University of South Australia, aims to test a novel solution to halt unprecedented levels of corrosion in the country’s ageing concrete pipelines.
Corrosive acid from sulphur-oxidising bacteria in wastewater, in addition to excessive loads, internal pressure and temperature fluctuations cause pipes to crack and reduce their life span. This often results in hundreds of millions in annual repair costs in Australia.
To prevent this from happening self-healing concrete, in the form of microcapsules filled with water treatment sludge, could be the answer. Prof Zhuge stated that sludge waste shows could mitigate microbial corrosion in concrete sewer pipes as it serves as a healing agent to resist acid corrosion and heal the cracks.
Researchers will develop microcapsules with a pH-sensitive shell and a healing agent core containing alum sludge – a by-product of wastewater treatment plants – and calcium hydroxide powder. The combination will be highly resistant to microbially induced corrosion (MIC). It will be embedded inside the concrete at the final step of mixing to protect it from breakage. When the pH value changes as acid levels build up, microcapsules will release the healing agents.
The technology will not only extend the lifetime of concrete structures, saving the Australian economy more than AU$1 billion, but it will promote a circular economy as well by reusing sludge that would normally end up in a landfill.
Existing repairs of deteriorating concrete only cost millions and are often short-lived, with 20% cent failing after five years and 55% fail after 10 years. Moreover, current acid corrosion containment methods in sewer pipes have been unsuccessful for several reasons.
While chemicals can be added to wastewater to alter the sewer environment and stop corrosion, they contaminate the environment and are expensive. Another option involves increasing the speed of sewage flow by amending the pipe hydraulics, but this is not always effective. Surface coating is another popular option, but it is time-consuming, and the effect is temporary.
It was noted that improving the design of the concrete mixture is the ideal method for controlling microbially induced corrosion. Using self-healing concrete that can seal cracks by itself without any human intervention is the solution.
In addition, to achieve carbon neutrality by 2050, the construction industry must transition to a circular economy. Industry by-products or municipal wastes that would normally be discarded in landfill sites, potentially generating pollution, may now be reused in the construction production chain.
Alone, Mainland Australia has roughly 400 drinking water treatment plants, with a single site annually generating up to 2000 tonnes of treated water sludge. Most of that is disposed of in a landfill, incurring a cost of over AU$ 6 million annually, as well as resulting in extreme environmental damage.
Disposing of one tonne of sludge in a landfill releases approximately 29.4 tonnes of carbon dioxide emissions – much higher than cement production – and leaches aluminium into the soil and water, a risk factor for Alzheimer’s disease.
The team is confident that the novel self-healing concrete based on advanced composite technology will address issues of sewer pipe corrosion and sludge disposal in one hit. The project is being partially funded by an AU$ 501,504 Australian Research Council grant and involves researchers from the University of South Australia and the University of Queensland.
