Ask an Expert: Crumb Rubber Concrete

What happens to your cars tyres when you get new ones? One environmentally friendly option is to use the rubber from the old tyres to replace sand in concrete.

Dr Safat Al-Deen from UNSW Canberra is undertaking research into how to produce more environmentally concrete and explains how crumb rubber concrete is a solution to utilise tyre waste into a construction material.  

What is crumb rubber concrete?

The conventional concrete mix typically consists of cement, water, coarse aggregates like crushed stone, and fine aggregates like sand. The crumb rubber concrete is made by replacing some or all the sand in concrete with crumb rubber derived from scrap tyres. This crumb rubber is obtained by shredding the scrap tyres into small particles.

Given that cement production is a major source of carbon dioxide emissions and the components that make concrete have significant environmental impacts, alternative materials are sought to make concrete mixes more environmentally friendly.

Geopolymer concrete is one such alternative, known for its eco-friendliness. By substituting sand with scrap tyre-derived crumb rubber, we can produce geopolymer rubber concrete.

Why does tyre rubber waste make for a good alternative in concrete?

Concrete is everywhere and needs a lot of natural materials to make it. But these materials, like sand and gravel, are running out. Taking them from rivers and lakes is causing big environmental problems, and we're losing the natural filters that clean rainwater. To stop this pollution, rules are becoming stricter about taking these materials. Concrete is used a lot, so even using a little bit less of the natural stuff could save a lot. That's why we are looking into using old stuff, like recycled materials, to make concrete. But it's not always easy to get it right.

In Australia, like everywhere in the world, getting rid of old tyres is a big problem.

In 2022-23, Australia had 11.3 million used tyres that could not be repurposed and are being illegally dumped, landfilled or hidden on industrial sites. That is more than the population of Sydney and Melbourne combined, and it's getting harder to deal with them.

The piles keep growing, and it's tough to manage them properly. Old tyres can even start fires, pollute water, and make homes for bugs. They don't break down naturally and release lousy stuff into the air and water, making climate change worse.

Crumb rubber concrete was initially developed to tackle these two big problems: reducing the need for natural resources in making concrete and finding a solution for the growing scrap tyre issue.

What are the benefits of crumb rubber concrete compared to traditional concrete? 

Crumb Rubber Concrete (CRC) offers plenty of benefits compared to regular concrete.

It's not just about being eco-friendly – CRC also has some technical advantages over regular concrete for some special uses. It's less likely to crack, even in tough conditions, and can handle heavy impacts better than regular concrete.

This makes them suitable for roadside kerb and road safety barriers. And it's quieter too! The rubber in CRC soaks up sound, making it perfect for quieter roads and buildings.

Another great thing about CRC is that it helps keep things cool. Those rubber bits help regulate temperatures, which means less stress on concrete structures. Plus, it's got a better grip, so it's not as slippery on roads – perfect for safety!

It's lighter too! Because it replaces some of the usual materials with rubber, CRC is lighter and easier to handle. So, whether it's for building roads, bridges, or buildings, Crumb Rubber Concrete is a smart choice that's good for the environment and packed with cool features.

How do you see this sustainable construction material being used?

CRC offers a wide range of practical uses thanks to its special properties. For starters, CRC is perfect for building footpaths, roadside kerbs, driveways and road safety barriers. It is also great for bridge decks and overlays. It's super durable and can withstand all kinds of weather, reducing the chances of cracks and extending the life of bridges.

If you need to block out noise from highways or railways, CRC is your friend. Its sound-absorbing qualities make it ideal for constructing noise barriers. You can even use CRC to make eco-friendly building blocks for walls and garden beds. They offer insulation and soundproofing properties while being sustainable.

In some cases, CRC can even be used for structural elements like columns and beams in a high-rise building. We just need to make sure the right mix and testing are done for load-bearing applications. 

Why should we be using more sustainable construction material like this?

These materials help reduce our impact on the environment by conserving natural resources and minimising pollution. By using renewable resources and recycled materials, we can lessen the depletion of finite resources and decrease waste sent to landfills. This not only benefits the planet but also contributes to a healthier and more sustainable future for generations to come.

If geopolymer crumb rubber concrete is used, it significantly reduces greenhouse gas emissions associated with traditional concrete production.  Traditional concrete relies on something called Portland cement, which releases a lot of carbon dioxide into the air when it's made.

But with geopolymer concrete, we use alternatives like fly ash, slag, or special binders that don't need that high-temperature process, which is a big source of emissions. So, by choosing geopolymer crumb rubber concrete, we're making a greener choice that helps tackle climate change by reducing our carbon footprint.