Steel reinforced concrete will begin to rust over time, leading to costly damage. Roads & Infrastructure Magazine explores the issue of concrete cancer and the alternatives to steel out there.
Concrete has been used in construction around the world for thousands of years. Today, concrete relics like Rome’s Pantheon remind the world just how resilient concrete can be.
To ensure that buildings last longer and to provide further structural integrity, designers and engineers began reinforcing concrete with steel in the early 20th Century.
However, Guy Keulemans, a designer and researcher from the University of New South Wales, says this has created a monstrous hybrid. He says historian Robert Courland estimates the United States will likely suffer trillions in repair costs for buildings and infrastructure made from reinforced concrete.
“Concrete is the second most widely used material in the world after water. The main problem with concrete is it takes a huge amount of greenhouse gasses to create cement. It’s one of the big four when it comes to emissions, alongside coal fire, transport and agriculture,” Dr. Keulemans says.
“As a material, it’s really durable when used in the right way. The ancient Roman’s relatively sophisticated techniques means architecture like the Pantheon is still standing today. A lot of the issues that reinforced concrete faces in the long term actually come from the steel inside.”
Concrete cancer is the slow process of rust that builds up on internal steel within a section of reinforced concrete. Dr. Keulemans says steel will eventually rust and can expand the interior steel up to three or four times the original size, pushing the concrete apart. This damage can usually be repaired, but it is very costly.
“Repairing the damage involves stripping the concrete, replacing the rebar and reworking it. This can often cost more than recreating the entire building itself, so is usually reserved for buildings of great architectural importance,” Dr. Keulemans says.
The US was an early adopter of reinforced concrete and is now seeing the long-term effects within its infrastructure, Dr. Keulemans says.
“A lot of the structures built within the first half of the 20th Century are now falling apart. The Florida Keys has suffered significant issues due to the high salt environment and may need large sections of its infrastructure replaced.
“This cost will be given to future generations as the infrastructure starts to require repairs. Because it was cheap, strong and had the ability to create architectural marvels, steel reinforced concrete was aggressively promoted in the first half of the 20th Century,” he adds.
Dr. Keulemans says to improve sustainability in infrastructure means using materials that will last for centuries instead of decades.
“As technology progresses, we’ve seen new materials become viable for certain building applications. For example, engineered timber buildings are a growth area, with office buildings being built in Europe and Australia that capture carbon instead of emitting it,” he says.
“Other methods of reinforcing concrete could be certain types of plastics or carbon fibres. There’s even the possibility of unconventional materials like aluminium-bronze or bamboo being used, although these are often more expensive and difficult for government approvals.”
For civil applications like drains, footpaths, bikeways and pavements, steel is still in use as a reinforcing mesh. Australian company Fibercon has found a way to replace this with recycled plastic fibres, called Emesh, to give footpaths more longevity.
While it is not appropriate for buildings or bridges, Tony Collister, head of Research and Development at Fibercon, says Emesh provides a resilient and long-lasting material.
Mr. Collister says this method reduces greenhouse gas emissions by more than 90 per cent and ends up saving time and being cost effective on a material basis.
Developed in partnership with James Cook University (JCU), Emesh has been used in a number of footpaths at the JCU campus in North Queensland and throughout some of Queensland’s councils. Emesh uses offcuts and plastics from industrial waste, which is then used to reinforce the concrete.
“By replacing the steel mesh in concrete with plastic, the pavement is protected from concrete cancers. Usually, pavement will crack over time allowing oxygen and moisture to reach the steel. This leads to oxidisation of the steel and eventually destroys the footpath in 20 to 25 years,” Mr. Collister says.
While plastic fibres have been available for more than 20 years, Mr. Collister says using recycled material helps the environment by reducing landfill, reducing greenhouse gas emissions and water usage.
“Approximately 25 million cubic metres of concrete is used in Australia a year. Ensuring the creation of a circular economy through alternatives is an important start for a smarter future,” he says.
“The intention is to do something to give back, to close the cycle of useless waste,” he says.