The team from RMIT University in Melbourne has developed a new manufacturing process that replaces 100 per cent of the traditional coarse aggregates in concrete mix (like gravel and crushed rock) with rubber from old tyres.

Previously, researchers have used small amounts of recycled rubber in concrete but replacing 100 per cent of the aggregate with rubber led to poor performance and a reduction in strength, hindering its application in the concrete industry.

RMIT University’s research has overcome these challenges, developing a way to increase the strength of rubberised concrete without applying complex, time-consuming, and cost-ineffective pre-treatments to the rubber. The technique involves using newly designed casting moulds to compress the coarse rubber aggregate in fresh concrete, enhancing the building material’s performance.

Lead author of the research at RMIT University’s School of Engineering, Mohammad Momeen Ul Islam, said the results have surpassed what was previously thought to be possible.

“We have demonstrated with our precise casting method that this decades-old perceived limitation on using large amounts of coarse rubber particles in concrete can now be overcome,” Islam said.

The research team believes the new method will significantly reduce manufacturing and transportation costs and grow the market for recycled rubber from used tyres.

“As a major portion of typical concrete is coarse aggregate, replacing all of this with used tyre rubber can significantly reduce the consumption of natural resources and also address the major environmental challenge of what to do with used tyres,” said team leader and co-author of the study, Professor Jie Li.

According to the 2020 National Waste Report, Australians generate more than 400 kilotonnes (thousands of tonnes) of used tyres every year, and at least 10 million tonnes of tyres have already been buried or landfilled nationally.

As part of the Australian Government’s National Waste Policy Action Plan and in response to China’s restrictions on accepted imported materials, the export of used tyres has been banned since December 2021. This has presented an urgent challenge to find new markets for recycled rubber to accommodate the increasing amount of tyre waste generated in Australia each year.

The research team at RMIT University said the new manufacturing process could be scaled up cost-effectively within a precast concrete industrial setting in Australia and overseas, creating exciting possibilities for a new construction material with promising environmental credentials.