Concrete Made From Recycled Tyre Rubber Meets Building Strength Standards

A potential good news story for sustainability and the circular economy has emerged from Melbourne where engineers have cracked a new method to replace all of the conventional aggregates normally used in concrete with rubber. These traditional aggregates such as crushed rock and gravel have been replaced with recycled rubber from tyres.

Lead Author and PhD researcher, Mohammad Momeen UI Islam, said,

“Recently, we have developed a technique that will allow us to generate structural grade lightweight concrete for the complete replacement of traditional coarse aggregate by waste rubber aggregates.”

Up until recently, all attempts made to replace the material in concrete with rubber have resulted in weak concretes that do not meet the required building standards. However, engineers at the Royal Institute of Technology (RMIT) University in Australia have recently succeeded in replacing 100% of conventional aggregates in concrete, such as gravel and crushed stone with rubber from recycled tyres.

Their recent study has unveiled a manufacturing process for structural, lightweight yet strong concrete in which the coarse aggregates have been replaced entirely by rubber.

The resulting concrete is tougher than regular concrete as the rubber particles within it allow it to bend under pressure instead of breaking.

Mohammad Momeen UI Islam, stated,

“We have demonstrated that 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.”

According to the team, this new concrete meets the strength standards required by building regulations.

It is believed that this new lighter more environmentally friendly concrete will also yield both environmental and economic benefits. This tyre rubber-based concrete has the potential to significantly lower manufacturing and transport costs.

As a bonus, this new concrete also addresses another environmental challenge of figuring out how to dispose of used tyres.

Used tyres can be recycled to some extent but most of the time they just end up being left in landfills or getting burnt. The new manufacturing process for concrete avoids the tyres taking up space at landfills or releasing toxic gasses into the atmosphere.

Professor Jie Li, Study co-author and Team Leader said:

“As a major portion of typical concrete is coarse aggregate, replacing all of this with used tire rubber can significantly reduce the consumption of natural resources and address the major environmental challenge of what to do with used tyres.”

The idea of replacing the aggregate found in concrete with rubber tyres is not new.

Past scientists have tried and failed. The researchers at the Royal Institute of Technology (RMIT) University in Australia have put this failure down to poor bonding due to the porosity of the tyre rubber. This porosity causes pores in the rubber to fill with water when the concrete is initially mixed, however, once the concrete sets, the water evaporates leaving empty voids at the rubber/cement interface.

To address this problem the team of engineers placed wet concrete in special steel moulds that put pressure on the concrete and compress the particles and the pores within them. This results in cement that is much better bonded to the ‘preload’ tyre particles.

Mohammad Momeen UI Islam, Lead Author and PhD researcher said:

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

This new type of concrete is still in the early stages but having completed successful workshop testing the team is now investigating and looking for new ways to reinforce the concrete, making it even better suited to be used in construction projects.

Although this new concrete is still in its early stages, it is showing signs of promise. Concrete made using rubber tyres is stronger than traditional concrete, is cheaper to make, and addresses many environmental issues such as repurposing used tyres. Further research needs to be done to check suitability for construction projects, but early signs are promising.