RMIT University researchers have found a surprising new way to replace conventional concrete aggregates in the transport industry.

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

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 of 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,” Islam 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.” 

Study co-author and team leader Professor Jie Li says this manufacturing process will unlock environmental and economic benefits.

“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,” he says.

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. 

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