Stories

Globally, around 1.5 billion tires are discarded each year, with many ending up in landfill. As they slowly fragment over time, they leech toxic chemicals into the soil and groundwater, causing long term environmental damage. Stockpiled tires also pose significant public safety risks, as they are highly combustible and difficult to extinguish once ignited. They can also accumulate water that creates breeding grounds for pests such as mosquitoes and vermin.

Because of this, end‑of‑life tires remain a complex policy issue for governments worldwide, with researchers and industry stakeholders exploring viable alternative uses.

This was the focus of KBR’s Senior Principal Structural Engineer, Dr. Mark Ellis’ PhD research. In partnership with fellow researchers from the University of South Australia, Mark’s research explored various ways to recycle more rubber tires. Specifically, they looked into rubberized concrete – concrete that replaces sand with small pieces, or crumbs, of old recycled tires – for use in the residential building industry. Mark’s focus was longevity of rubberized concrete through a series of durability tests on this green concrete.

Putting rubberized concrete to the test

In order to test the durability of rubberized concrete, Mark’s team wanted to test it against the things that usually cause concrete to deteriorate over time – water, salt and carbon dioxide, which can pass through concrete and reach the steel reinforcement inside. Large residential slabs made with crumbed rubber concrete were monitored both via a real-life test construction site and also in the lab.

The results showed that overall, crumbed rubber concrete performs in a similar way to standard concrete when it comes to durability and reinforcement protection. A positive result that could give end-of-life tires a new lease on life. 

Mark said this is a positive result in more ways than one, “We crunched the numbers and worked out that if crumbed rubber replaced just 20% of the sand used in residential concrete, Australia could use up all the tires currently sent to landfill each year. 

“The environmental benefits of repurposing tires in this way and preventing them from going to landfill would be significant. But it has an additional benefit in that the sand currently being used for concrete is getting harder and harder to source, so we need to find an alternative to sand for concrete anyway. Taking toxic tires out of landfill while also reducing the natural sand resources we’re using in construction is a win-win.”

KBR embracing circularity to help decarbonize the building industry 

Mark’s PhD research helps inform KBR’s focus on delivering sustainable, future focused solutions for our clients. This includes exploring low carbon concrete alternatives and industry byproducts to replace cement, opting for recycled steel materials, and utilizing locally manufactured materials to increase transport efficiencies and support local industry. It also includes supporting adaptive reuses and repurposing of existing buildings, as opposed to demolition and reconstruction.

Having lectured at the University of South Australia for more than eight years, and continuing to work closely with the university mentoring PhD students, Mark keeps across the latest developments in recycled and low-carbon building materials. He draws on this expertise to advise KBR customers who are looking to reduce their carbon footprint. 

“The uptake for low-carbon and recycled building materials in Australia is still reasonably slow. Partly due to costs, but also partly due to a general lack of awareness of, and trust in, the alternatives. However, the tides are starting to shift and we’re hearing from more and more customers interested in exploring sustainable alternatives. Particularly from schools and government-owned buildings. 

“The great news is that there are so many more options available today than there have been previously. And as structural engineers, we can advise customers on not only the most sustainable materials, but the ones that are the most structurally sound.”

KBR's tire recycling technology 

Material recycling and chemical recycling are complementary pathways, serving different end uses and scales of application. Material reuse applications (discussed in this article) provide valuable outlets for tire-derived rubber in suitable construction markets. Advanced thermal recycling, such as KBR’s TyreNova technology, offers a complementary commercial-scale pathway for recovering hydrocarbon and carbon value from end-of-life tires through the production of tire pyrolysis oil (TPO), recovered carbon black (rCB), recovered steel and process gas.