Engineers Use Tire Rubber for Concrete Aggregates


A team from the Royal Melbourne Institute of Technology (RMIT) University reported they have replaced 100% of conventional aggregates in concrete with rubber from discarded tires to promote a circular economy.

According to the study that was recently published in the journal Resources, Conservation & Recycling, the engineers say the new greener, lighter concrete also can reduce manufacturing and transportation costs significantly.

About the Research

While small amounts of rubber particles from tires have previously been used to replace concrete aggregates, RMIT reports that the rubber replacements have produced weak concretes that fail to meet the required standards.

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

Because used tires in Australia cannot be exported, methods for recycling and reprocessing them locally has become “increasingly important.” Study co-author and team leader, Professor Jie Li, said 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 tire rubber can significantly reduce the consumption of natural resources and also address the major environmental challenge of what to do with used tires,” he said.

About 1.2 billion waste tires are expected to be disposed of annually worldwide by 2030. Li added the new concrete could also greatly reduce manufacturing and transportation costs.

“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,” he said.

The technology reportedly builds on the invention of the technique by RMIT University Engineers Professor Yufei Wu, Dr. Syed Kazmi, Dr. Muhammad Munir and Shenzhen University's Professor Yingwu Zhou. The research team also includes Professor Yu-Fei Wu, Dr. Rajeev Roychand and Dr. Mohammad Saberian.

For its next steps, the team is looking into reinforcing the concrete to see how it can work in structural elements.

The researchers hope the process could be scaled up cost effectively within a precast concrete industrial setting in Australia and overseas. The university added that several national phase patent applications have been filed for the process.

Rubber in Concrete Research

Back in 2019, researchers from the Department of Civil and Structural Engineering at The University of Sheffield (South Yorkshire, England) had reportedly found a new way of protecting concrete from fire damage. The team has tested a technique of using fibers extracted from recycled tires and adding them to the concrete mix. The process, according to researchers, has shown to reduce the concrete’s tendency to spall.

Though some modern projects have used concrete that includes polypropylene to protect against fire spalling, this research set out to show that that the fibers do not need to be made from raw materials, but instead can be used from recycled tires.

According to the university, the team plans to continue testing the material with different ratios of the fibers to concrete, and also using different types of concrete. They also plan to find out more about how the materials react to heat at the microstructure level.

In April 2021, researchers at Rice University said they optimized a process to convert waste from rubber tires into graphene that can then be used to strengthen concrete.

While it is acknowledged that recycled tire waste is already used in Portland cement, the Rice researchers note that graphene itself has been proven to strengthen cementitious materials at the molecular level.

To recover the graphene from the tires, the researchers are using a “flash” process that they introduced in 2020. The process exposes material to a jolt of electricity that removes everything but the carbon atoms. Those atoms then reassemble into turbostratic graphene, which is more soluble that graphene produced from graphite and therefore easier to use in composite materials.

 According to Rice, the lab flashed tire-derived carbon black and found about 70% of the material converted to graphene. When flashing shredded rubber tires mixed with plain carbon black to add conductivity, about 47% converted to graphene. (Elements besides carbon were vented out for other uses.)

For the actual process, the electrical pulses lasted between 300 milliseconds and one second. The lab calculated that the electricity used in the conversion process costs about $100 per ton of starting carbon.

The researchers then blended minute amounts of tire-derived graphene—0.1 weight/percent (wt%) for tire carbon black and 0.05 wt% for carbon black and shredded tires—with Portland cement and used it to produce concrete cylinders.

After curing for seven days, the cylinders showed gains of 30% or more in compressive strength. After 28 days, 0.1 wt% of graphene sufficed to give both products a strength gain of at least 30%.


Tagged categories: Asia Pacific; Australia; Colleges and Universities; concrete; Environmental Controls; Environmentally friendly; Good Technical Practice; Green building; OC; Program/Project Management; Projects - Commercial; Recycled building materials; Research and development; Sustainability

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