Self-healing concrete could save sewer pipes
Water treatment sludge could be used to prevent 117,000km of sewer pipes in Australia from cracking in future, without any intervention by humans, helping to save $1.4 billion in annual maintenance costs.
A research project, led by University of South Australia sustainable engineering expert Professor Yan Zhuge, is trialling a novel solution to halt unprecedented levels of corrosion in the country’s ageing concrete pipelines.
Corrosive acid from sulphur-oxidising bacteria in wastewater, along with excessive loads, internal pressure and temperature fluctuations is cracking pipes and reducing their life span, 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.
“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,” Yan says.
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.
Existing repairs of deteriorating concrete not only cost millions, but they are often short-lived, with 20% failing after five years and 55% failing after ten years. 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 another 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,” Yan explains.
The project is being partially funded by a $501,504 Australian Research Council grant and involves researchers from the University of South Australia and the University of Queensland.
Photo by Sharon Waldron on Unsplash