Researchers have found a way to convert rubber from discarded tires into the strong carbon nanomaterial graphene. Adding this graphene to concrete makes the concrete stronger and more sustainable.
With urban jungles on the rise, concrete has become the most-produced material in the world. Its production results in nine percent of global carbon emissions. To reduce those emissions, researchers have tried to boost its ability to absorb carbon dioxide or use less carbon-intensive alternatives to cement, the main ingredient in concrete.
The new research presented in the journal Carbon could shrink the carbon footprint of concrete while addressing the problem of waste tires. Almost a billion tires are scrapped around the world every year. Around 16 percent of them end up in landfills, but most are either ground up for other uses or burned for fuel, including fuel for cement kilns. Last year, a team in Australia made a road-building material by blending crushed concrete with shredded tires.
The team from Rice University and C-Crete Technologies in Stafford, TX decided to convert waste tires into graphene, which has been shown before to strengthen concrete.
They used a graphene-production technique developed at Rice called flash heating, which involves superheating carbon sources such as food waste or plastic with a jolt of electricity. The process removes everything else besides carbon atoms, which rearrange into graphene flakes.
The team found that rubber is harder to turn into graphene. So they used the black waste material that is leftover after tires have gone through a recycling process to extract oil. They could convert about 70 percent of this carbon black residue into graphene with flash heating.
Next, they added tiny amounts of this graphene to Portland cement and used it to make concrete cylinders. After seven days of curing, tests showed that the graphene-infused cylinders were 30 percent stronger than regular concrete.
Flash heating is an easy and inexpensive way to produce graphene from rubber tire waste that would otherwise be burned for fuel or disposed in landfills, the researchers write in the paper,
Source: Paul A. Advincula et al. Flash graphene from rubber waste. Carbon, 2021.
Photo: Photo: Octavi Serra/ Pneumatic. Street art installation in Barcelona.