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Managing used mask waste has been among the biggest environmental challenges since the very beginning of the COVID-19 pandemic. But what if we can process them while making our construction materials even more efficient?
A new study has shown that incorporating old masks into concrete can make it stronger and reduce its dependency on carbon-intensive cement.
The study, conducted by a team of researchers from Washington State University and published in the journal Materials Letters, showed that when old medical masks were processed and used in a concrete mix, it resulted in a 47% increase in splitting tensile strength increase after a curing period of 28 days.
The split tensile strength of concrete indicates its total tensile strength. While concrete displays exceptional compressive strength — which makes it a highly sought after building material — it suffers from a distinct lack of tensile strength. This is the reason reinforcement bars are used to stabilise concrete. Remember Reinforced Cement Concrete?
To be more precise, this lack of tensile strength primarily arises from the Interfacial Transition Zone (ITZ) — which is a weak region between the different materials in the concrete mix. Another way the tensile strength is increased in the mix is with the addition of Secondary Cementitious Materials, such as fly ash, silica fumes and slag cement. Microfibers are also sometimes added to cement concrete to strengthen it, but they’re expensive. And that’s where the discarded masks can come in handy?
In this experiment, the microfibers obtained from recycled medical masks — primarily polypropylene or polyester fabrics — were pre-treated in an aqueous solution of graphene oxide (GO) to improve the ITZ between the mask fibres and the cement paste matrix. These were then incorporated into ordinary portland cement for testing.
The fracture energy that might otherwise contribute to microscopic cracks in the concrete is absorbed or dissipated by the mask microfibers. These small flaws would eventually lead to larger cracks and concrete failure under loads. The GO helps in creating ultrathin layers that stick to the fibre surfaces aggressively.
This study preliminarily demonstrated the feasibility to upcycle waste masks in the concrete industry and provided a new strategy for disposing of waste masks.
“These waste masks actually could be a valuable commodity if you process them properly,” said Xianming Shi, professor and interim chair of the Department of Civil and Environmental Engineering and the corresponding author of the paper.
Disposable masks contribute significantly to plastic pollution. According to Ocean Asia’s 2020 report, 1.6 billion disposable masks ended up in the oceans in 2020, amounting to approximately 5,500 tons of plastic. These single-use masks take around 450 years to biodegrade naturally and pose considerable environmental risks to ecosystems.
Further, the production of cement is a carbon-intensive process, responsible for as much as 8% of carbon emissions worldwide, the paper asserts.
The researchers plan to use this technique the strengthen concrete-based roadways, and reduce the amount of deicing chemicals used to protect against frost damage. They also plan to use this technique to encourage the collection and recycling of other polymer items, such as abandoned clothing.
“This work showcases one technology to divert the used masks from the waste stream to a high-value application,” Shi commented.
The study was published in the journal Materials Letters earlier this month and can be accessed here.
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