Concrete’s enormous environmental footprint has led researchers in recent years to come up with greener versions of the building material. Now, engineers at RMIT University in Australia have replaced all of the coarse rocky material that makes up the bulk of concrete with waste rubber from used tires.
It’s a way to use up some of the one billion or so scrap tires that the world produces every year. Most of these get buried in landfill and leach toxic chemicals into the ground, or are burned, creating carbon dioxide emissions. Plus, it would reduce the need for natural materials like rocks used in concrete that are mined, and are expensive due to high demand.
“Utilizing waste to make concrete can solve environmental issues and play a significant role in the circular economy,” says Mohammad Momeen Ul Islam, lead author of the paper published in the journal Resources, Conservation and Recycling.
Two years ago, the RMIT team blended scrap tire rubber with crushed concrete to make the base layers of roads that are covered with asphalt. They have now found a use for waste tire rubber to make the concrete itself.
Concrete is a mixture of aggregate materials like sand, gravel and rocks that is held together by a paste of cement and water. Researchers have previously swapped some of the sand and gravel that goes into concrete with used rubber tires. Real-world tests show that this rubber based concrete works even better than conventional concrete in many ways.
Efforts to replace all of the aggregates with rubber have resulted in weak concrete that failed to meet required standards. That’s because the rubber aggregate has too many pores, so it requires more water during the concrete mixing process. The water fills the pores, but as it evaporates while the concrete dries, it leaves behind gaps between the rubber and the cement around it, reducing the strength of the concrete.
So Ul Islam and colleagues came up with a better way to mold concrete with 100% rubber aggregate. They put the wet mixture in molds and compress them to remove all the pores in the drying concrete. The resulting material is almost twice as strong as ones made before.
But for now, the concrete offers other advantages like being lighter than traditional concrete. “Our newly developed concrete is a structural lightweight concrete,” says Ul Islam. “Being lightweight, it will reduce the transportation cost, and being a precast concrete member, it will reduce the construction time and save the labor cost. Therefore, it will provide economic benefits.”
The researchers are now looking to increase the strength of their 100% rubber concrete even further. And they are seeking industry partners to implement this technique in structural elements, he says. “We hope it can be used in the construction industry very soon.
Source: Mohammad Momeen Ul Islam et al. Design and strength optimization method for the production of structural lightweight concrete: An experimental investigation for the complete replacement of conventional coarse aggregates by waste rubber particles. Resources, Conservation and Recycling, 2022.
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