Disposable masks could be used to improve concrete
With disposable masks widely used during the pandemic now posing an environmental problem, researchers have introduced the idea of incorporating old masks into a cement mix to make stronger, more durable concrete.
In a paper published in the journal Materials Letters, a team of researchers from Washington State University showed that the mixture of mask materials was 47% stronger than commonly used cement after curing for one month.
“These waste masks could actually be a valuable raw material if you process them properly,” said Xianming Shi, professor and interim chair of the Department of Civil and Environmental Engineering and corresponding author of the study. “I’m always on the lookout for waste streams, and my first reaction is, ‘How do I turn this into something useful for concrete or asphalt?’ ”
The production of cement is a carbon-intensive process, responsible for up to 8% of global carbon emissions. Sometimes microfibers are already added to cement concrete to strengthen it, but they are expensive. Microfiber-reinforced concrete can potentially reduce the amount of cement needed for a project or extend the life of the concrete, saving both carbon emissions and money for builders and owners.
Medical masks are made of a polypropylene or polyester fabric in the areas that come in contact with the skin and an ultra-fine polypropylene fiber for the filtration layers, and contain fibers that can be useful to the concrete industry. If not reused, disposable masks can remain in the environment for decades and pose a threat to the ecosystem.
“This work demonstrates a technology that can divert used masks from the waste stream into a high-value application,” Shi said.
In their proof-of-concept work, the researchers developed a process to make tiny mask fibers five to 30 millimeters long and then added them to cement concrete to strengthen it and prevent it from cracking. For their tests, they removed the metal and cotton loops from the masks, cut them up and mixed them into ordinary Portland cement, the most commonly used type of cement in the world and the basic ingredient in concrete, mortar and grout.
They mixed the masks’ microfibers with a solution of graphene oxide before adding the mixture to the cement slurry. The graphene oxide forms ultra-thin layers that strongly adhere to the fiber surfaces. Such masking microfibers absorb or dissipate fracture energy that would cause tiny cracks in the concrete. Without the fibers, these microscopic cracks would eventually lead to wider cracks and failure of the material.
The researchers are conducting further studies to test their idea that graphene oxide-treated microfibers could also improve the durability of concrete and protect it from frost damage and from deicing chemicals used on roads. They can also envision applying this technology to the recycling of other polymer materials, such as used clothing, to incentivize the collection of such waste.