About half of the waste produced worldwide every year can be attributed to construction, demolition, and renovation, and there are about one billion tires that are thrown away annually around the world [1].
Experts, governments, and organizations are looking for ways to cut down on this waste by moving toward what is known as a circular economy: an economic system of closed loops in which raw materials, components, and products lose their value as little as possible, renewable energy sources are used and systems thinking is at the core [2].
Reusing old materials is the ideal way to cut down on waste while also lessening our reliance on new or “virgin” materials. Engineers in Australia have now developed a new material for more durable roads based on this principle, using old tires as the base.
Recycling Tires for More Durable Roads
A team from RMIT University in Australia is using a blend of old tires and rubble left over from construction projects to make a new road material that is better able to handle the impact of traffic.
Recycled concrete aggregate (RCA) is already used as a base layer that goes beneath the asphalt layer on top, but the addition of tire crumbs improves its ability to handle the elements. Civil engineer Mohammed Saberian Boroujeni, part of the team who developed the material, says that traditional road bases are made of unsustainable virgin materials like quarried rock and sand.
“Our blended material is a 100 percent recycled alternative that offers a new way to reuse tyre and building waste, while performing strongly on key criteria like flexibility, strength, and permanent deformation.” [3]
In order to test the material, the team used machines that were designed to simulate the stress produced by passing vehicles over time. This allowed them to tweak the “recipe” in order to find the correct ratio of rubber to RCA, which turned out to be 0.5 percent fine crumb rubber to 99.5 percent RCA [3].
The Anatomy of a Road
There are four layers that make up a road: a subgrade, a base, a sub-base, and an asphalt layer on top. Each layer must be strong enough to withstand the pressure of heavy vehicles, while also being flexible enough to prevent the road from cracking over time.
While RCA can work alone as a base layer, adding the recycled rubber to it improves its strength and durability. The research team in Australia demonstrated during tests that their blend of rubble and rubber performed well when tested for stress, acid and water resistance, as well as strength, deformation and dynamic properties. It also shows less shrinkage and greater flexibility to prevent cracking [1].
Better Roads, Cleaner Environment
Chief investigator Professor Jie Li says that both the construction and scrap tire industries are still producing significantly more waste than what is being reused, but recycling in both areas is on the rise.
“Solutions to our waste problems will come not only from reducing how much goes to landfill and increasing how much we recycle; developing new and innovative uses for our recycled materials is absolutely vital,” said Li [1].
Boroujeni believes that their recycled blend is the right choice for better roads and a better environment, as industries push toward a circular economy that eliminates waste and does a more efficient and effective job at reusing resources [3].
Currently, in Australia, only sixteen percent of scrap tires are recycled domestically, and about 3.15 million tons of RCA is added to stockpiles every year as opposed to being reused. For this reason, the Australian government banned the export of certain waste materials in 2019, with the goal of building Australia’s capacity to generate high-value recycled commodities [1].
Tire Recycling Around the World
Car tires present a major waste problem globally. While they can be retread and reused up to a point, this cannot be done indefinitely. End of life tires (ELTs) are difficult to recycle because they are made with a complex mix of materials. They don’t biodegrade so they are often left to pile up in landfills.
Tires in landfills are problematic because as they sit there they leach toxins into the soil and water, which creates a significant health risk. Tire dumps are a fire risk, and when they do catch fire they are notoriously difficult to put out.
As more and more cars are put on the road every year, figuring out what to do with ELTs is becoming increasingly important. As such, a variety of strategies to deal with them have emerged, and the European Union has led the charge. Today, one hundred percent of tires are processed in some way in continental Europe [4].
Dealing With The Problem
There are a number of innovative ways Europe has used to deal with their tire problem, the most prominent of which is burning them for electricity or heat generation. This practice is known as “energy recovery”, and about half of Europe’s tires are used in this way.
Tires are just as dense as coal but they don’t produce nitrous oxides, making them a greener fuel source than coal. Tires do, however, produce some pollutants. By using the correct method of burning and scrubbing technologies, this impact can be reduced.
Businesses across the EU have begun using tires in many areas, including as the base for rubber tracks and playground surfaces, asphalt, and of course roads.
Railways have also begun using recycled tires as fitted rubber pads underneath railway or tram tracks to reduce noise and vibration [4].
More and more cars are put on the roads every year. This is why putting strategies in place to deal with the used tires they generate will become more important than ever. The more we can repurpose old materials like ELTs for other uses, and the closer we can get to a circular economy, the better off our planet will be.
Sources
- “How to mix old tyres and building rubble to make sustainable roads.” RMIT.
- “What is the definition of a circular economy?” Kennis Kaarten.
- “Engineers Have Found a Way to Make More Durable Roads Out of Old Tyres And Rubble.” Science Alert. David Nield.
- “What can the world do with 1.5 billion waste tyres?” Earth Bound. Jeremy Williams.