Engineers in Australia have come up with an innovative solution to use two large sources of waste that end up in landfills: scrap tires and construction rubble. Mixing the two gives a sustainable material to build roads, they report in the journal Construction and Building Materials.
The construction and demolition industry generates about half of all the world’s waste. Crushed concrete makes up the biggest part of this waste. And a small percentage of it reused to make roads and sidewalks.
Tires create a similar waste problem. Around one billion scrap tires are produced around the world every year, a number that will increase as we see more and more vehicles on the road. Most of these end up in landfills or incinerated, creating a huge amount of carbon dioxide emissions and toxic chemicals leaching into groundwater.
Crushed concrete is used to make the base layers of roads that are topped with asphalt. But the team from RMIT University in Melbourne found that blending the crushed concrete with scrap tire rubber gives a material that works better.
The researchers came up with a simple process to blend the two waste materials. They first dried the concrete rubble in an oven for two days, then add just a specific amount of water along with tire rubber crumbs, and blend the mixture in a large commercial mixer.
Tests showed that the rubber-rubble blend is resistant to acid and water, and strong enough to bear the weight of heavy vehicles. But it is also more flexible than plain crushed concrete, and better resists deformation and shrinkage, so it can bear weight without cracking as easily.
The researchers used a special machine to test how the blend would handle the pressures of being driven over by countless vehicles over its lifetime, and found that a mix of 0.5% fine crumb rubber and 99.5% crushed concrete gave the best performance.
“Our blended material is a 100% recycled alternative that offers a new way to reuse tire and building waste,” said Mohammad Boroujeni, who led the research. “As we push towards a circular economy that can eliminate waste and support the continual use of resources, our recycled blend is the right choice for better roads and a better environment.”
Source: Mohammad Saberian et al. An experimental study on the shear behaviour of recycled concrete aggregate incorporating recycled tyre waste. Construction and Building Materials, 2020.
