Recycled tyre rubber used as aggregate for concrete

The team in Melbourne, Australia said small amounts of rubber particles from tyres are already used to replace concrete aggregates, but efforts to replace all of the aggregates with rubber have produced weak concretes that failed to meet the required standards.

The study published in the Resources, Conservation & Recycling journal describes 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, said 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 said in a statement. “The technique involves using newly designed casting moulds to compress the coarse rubber aggregate in fresh concrete that enhances the building material’s performance.”

“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 study co-author and team leader, Professor Jie Li.

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 greener and lighter concrete could also greatly reduce manufacturing and transportation costs, Li said.

“This would benefit a range of developments including low-cost housing projects in rural and remote parts of Australia and other countries around the world.”

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

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