Engineers in Melbourne have discovered a way to replace 100% of conventional aggregates in concrete – such as gravel and crushed rock – with rubber from discarded tyres that meet building codes, promising a boost for the circular economy.

The team from RMIT University says the new greener and lighter concrete also promises to reduce manufacturing and transportation costs significantly.

Small amounts of rubber particles from tyres are already used to replace these concrete aggregates, but efforts to replace all the aggregates with rubber have produced weak concretes that failed to meet the required standards – until now.

The study published in the Resources, Conservation & Recycling journal reveals a manufacturing process for structural lightweight concrete where the traditional coarse aggregates in the mix were completely replaced by rubber from used car tyres.

Lead author and PhD researcher from RMIT University’s School of Engineering, Mohammad Momeen Ul Islam, says the findings debunked a popular theory on what could be achieved with recycled rubber particles in concrete.

“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,” he says.

“The technique involves using newly designed casting moulds to compress the coarse rubber aggregate in fresh concrete that enhances the building material’s performance.”

Used tyres in Australia cannot be exported, making new methods for recycling and reprocessing them locally increasingly important. About 1.2 billion waste tyres will be disposed of annually worldwide by 2030.

The team’s manufacturing process could be scaled up cost-effectively within a precast concrete industrial setting in Australia and overseas, Momee adds.

Following successful testing in the workshop, the team is now looking into reinforcing the concrete to see how it can work in structural elements.