Rice University scientists in the United States have optimised a process to convert waste from rubber tyres into graphene that can, in turn, be used to strengthen concrete.
The environmental benefits of adding graphene to concrete are clear, chemist James Tour says.
“Concrete is the most-produced material in the world, and simply making it produces as much as 9% of the world’s carbon dioxide emissions,” he says.
“If we can use less concrete in our roads, buildings and bridges, we can eliminate some of the emissions at the very start.”
Recycled tyre waste is already used as a component of Portland Cement, but graphene has been proven to strengthen cementitious materials, concrete among them, at the molecular level.
While the majority of the 800 million tyres discarded annually worldwide are burned for fuel or ground up for other applications, 16% of them wind up in landfills.
“Reclaiming even a fraction of those as graphene will keep millions of tires from reaching landfills,” Tour says.
The “flash” process introduced by Tour and his colleagues in 2020 has been used to convert food waste, plastic and other carbon sources by exposing them to a jolt of electricity that removes everything but carbon atoms from the sample.
Those atoms reassemble into valuable turbostratic graphene, which has misaligned layers that are more soluble than graphene produced via exfoliation from graphite. That makes it easier to use in composite materials.
Rubber proved more challenging than food or plastic to turn into graphene, but the lab optimised the process by using commercial pyrolyzed waste rubber from tyres.
After useful oils are extracted from waste tyres, this carbon residue has until now had near-zero value, Tour says.
Tyre-derived carbon black or a blend of shredded rubber tyres and commercial carbon black can be flashed into graphene. Because turbostratic graphene is soluble, it can then easily be added to cement to make more environmentally-friendly concrete.