A world-first project from the University of South Australia (UniSA) (Adelaide, South Australia) is trailing a novel solution to halt unprecedented levels of corrosion in Australia’s aging concrete pipelines.
Corrosive acid from sulfur-oxidizing bacteria in wastewater, along with excessive loads, internal pressure, and temperature fluctuations, are cracking pipes and reducing their life span—thereby costing hundreds of millions of dollars to repair every year across Australia.
Self-healing concrete, in the form of microcapsules filled with water treatment sludge, could be the answer to this issue. This sludge could be used to prevent 117,000 km (72,700.4 m) of sewer pipes in Australia from cracking in the future, without any intervention from humans, helping to save $1.4 billion in annual maintenance costs.
Background on Researchers
The project is led by Yan Zhuge, a sustainable engineering expert at UniSA STEM and a renowned expert in sustainable concrete material. Over the past five years, she has attracted more than $4 million worth of grants and published in 149 journal papers. In 2018, Zhuge won the South Australian Innovation Award in Engineering for her research on using waste in concrete.
“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,” Zhuge says.
Researchers will develop microcapsules with a pH-sensitive shell and a healing agent core containing alum sludge—a by-product of wastewater treatment plans—and calcium hydroxide powder. The combination will be highly resistant to microbially induced corrosion and 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.
Extending Structural Lifespans
“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 as reusing sludge that would normally end up in landfill,” says Zhuge.
Existing repairs of deteriorating concrete not only cost millions, but also are often short-lived—20% of repairs fail after five years and 55% fail after 10% years. In addition, existing methods to contain acid corrosion in sewer pipes are unsuccessful for a variety of reasons. Chemicals can be added to wastewater to alter the sewer environment and stop corrosion, but they contaminate the environment and are also costly.
Another option involves increasing the speed of sewage flow by amending the pipe hydraulics, but this is not always effective. Surface coating is a popular option, but it is time consuming, and the effect is temporary.
“Improving the concrete mixture design is the preferred method for controlling microbially induced corrosion. Using self-healing concrete that can seal cracks by itself without any human intervention is the solution,” Zhuge says.
Other Environmental Benefits
To be carbon-neutral by 2050, the construction industry is being forced to transit to a circular economy, Zhuge says.
“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,” she says. “Mainland Australia alone has about 400 drinking water treatment plants, with a single site annually generating up to 2,000 tonnes [2,204.6 U.S. tons] of treated water sludge. Most of that is disposed of in landfill, costing more than $6 million each year, as well as causing severe environmental issues.”
Disposing one tonne (1.1 U.S. ton) of sludge in landfill releases approximately 29.4 tonnes (32.4 U.S. tons) of carbon dioxide emissions—much higher than cement production—and leaches aluminum into the soil and water, a risk factor for Alzheimer’s disease.
“We are confident this novel self-healing concrete based on advance composite technology will address issues of sewer pipe corrosion and sludge disposal in one hit,” Zhuge says.
The project is being partially funded by a $501,504 Australian Research Council grant and involves researchers from UniSA and the University of Queensland.
Source: University of South Australia, www.unisa.edu.au.
Editor’s note: This article is repurposed from the February 2023 print issue of Materials Performance (MP) Magazine.