Rice University researchers have developed a new process to convert discarded tires into graphene, which can then be used to make noticeably stronger and environmentally friendly concrete.
Chemist James Tour, the study’s co-lead author, explained:
“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. If we can use less concrete in our roads, buildings, and bridges, we can eliminate some of the emissions at the very start.”
The breakthrough, published in the journal Carbon, builds on the team’s previous discoveries in making graphene via a process called flash Joule heating. This process involves exposing almost any carbon source to a jolt of electricity to quickly superheat it to around 4,940°F (2,725°C), removing everything but carbon atoms from the sample. Those atoms reassemble into valuable graphene flakes, known as turbostratic graphene, which has layers that don’t line up perfectly, making it more soluble, and easier to use in composite materials.
In 2020, the team demonstrated the technique using food waste, plastic, and other carbon sources – and now, they’ve moved onto old tires. The Rice team’s previous efforts to convert tires into graphene had near-zero value, so for the new study, they used a new substance – the remaining material left over after a standard recycling process called pyrolysis.
Pyrolysis involves burning tire waste in a low-oxygen environment. This process creates a very useful oil and a solid carbon residue that’s harder to find a use. However, the team found a use for it. This tire-derived carbon black proved to be very efficient at producing flash graphene. When they put it through flash Joule heating, around 70% of the material was converted into graphene, while a combination of commercial carbon black and shredded tire rubber yielded some 47%.
The researchers demonstrated how the new graphene material could be applied to concrete production. They added – 0.05 WT% for the mixture of shredded tire rubber and carbon black and 0.1 weight/percent (WT%) for the graphene made from tire carbon black – into Portland cement. The results showed that the concrete cylinders made with this cement had approximately 30% better compressive strength than concrete made without graphene.
Rouzbeh Shahsavari, the study’s co-lead author, added:
“This increase in strength is in part due to a seeding effect of 2D graphene for better growth of cement hydrate products, and in part due to a reinforcing effect at later stages.”
The Rice researchers highlight that the graphene-reinforced concrete has various environmental benefits, including:
- It prevents waste tires from ending up in the landfill;
- and the additional strength of the material could reduce the sum of concrete needed in structures.
Concrete isn’t the only thing that gets stronger when combined with graphene. In 2020, scientists from Pennsylvania State University discovered that graphene-reinforced carbon fiber is 225% stronger and 184% stiffer. Also, scientists from Brown University used a mix of graphene and ceramics to produce the toughest solid electrolyte to date.