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Turning single-use masks into strong, durable concrete

29 April 2022

Researchers have come up with an innovative way to tackle increased plastic waste caused by the pandemic: using disposable masks to strengthen concrete.

With the pervasive single-use masks during the pandemic now presenting an environmental problem, researchers have demonstrated the idea of incorporating old masks into a cement mixture to create stronger, more durable concrete. 
In a paper published in the journal, Materials Letters, a Washington State University research team showed that the mixture that was using mask materials was 47 percent stronger than commonly used cement after a month of curing. 

“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. 

“I’m always looking out for waste streams, and my first reaction is ‘how do I turn that into something usable in concrete or asphalt?’”

Production of cement is a carbon-intensive process, responsible for as much as eight percent of carbon emissions worldwide. Microfibres are already sometimes added to cement concrete to strengthen it, but they’re expensive. The microfibre-reinforced concrete can potentially reduce the amount of cement needed for a project or make the concrete last longer, saving carbon emissions as well as money for builders and owners.

Made of a polypropylene or polyester fabric where it contacts the skin and an ultra-fine polypropylene fibre for the filtering layers, medical masks have fibres that can be useful for the concrete industry. If they are not reused, disposable masks can remain in the environment for decades and pose a risk to the ecosystem. 

“This work showcases one technology to divert the used masks from the waste stream to a high-value application,” Shi said. 

The  researchers developed a process to fabricate tiny mask fibres, ranging from five to 30 millimetres in length, and then added them to cement concrete to strengthen it and prevent its cracking. For their testing, they removed the metal and cotton loops from the masks, cut them up and incorporated them into ordinary Portland cement, the most common type of cement used around the world and the basic ingredient for concrete, mortar and grout. 

They mixed the mask microfibres into a solution of graphene oxide before adding the mixture to cement paste. The graphene oxide provides ultrathin layers that strongly adhere to the fibre surfaces. Such mask microfibers absorb or dissipate the fracture energy that would contribute to tiny cracks in the concrete. Without the fibres, these microscopic cracks would eventually lead to wider cracks and the material’s failure. 

The researchers are conducting more studies to test their idea that the graphene oxide-treated microfibres could also improve the durability of the concrete and protect it from frost damage and from de-icing chemicals that are used on roadways. 

They also envision applying this technology to the recycling of other polymer materials, such as discarded clothing, to incentivise the collection of such waste.

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