Single-use masks could strengthen concrete

Published in Materials Letters, a team at Washington State University demonstrated that using waste materials from disposable masks could improve the mixture’s strength by 47 per cent, compared with commonly used cement after a month of curing.

“These waste masks actually could be a valuable commodity if you process them properly,” said co-author Xianming Shi, professor and interim chair of the Department of Civil and Environmental Engineering. “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?’”

Cement production is responsible for as much as eight per cent of worldwide carbon emissions. Microfibres are sometimes added to cement concrete to strengthen it, but are expensive. Microfibre-reinforced concrete can potentially reduce the amount of cement needed for a project or make the concrete last longer, reducing both cost and emissions.

Made of a polypropylene or polyester fabric where it contacts the skin and an ultra-fine polypropylene fibre for the filtering layers, medical masks’ fibres can be useful for the industry, researchers said. If not reused, disposable masks can remain in the environment for decades.

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

In their proof-of-concept work, researchers said they developed a process to fabricate tiny mask fibres ranging from five to 30mm in length, then added them to cement concrete to strengthen it and prevent its cracking.

For testing, they removed the metal and cotton loops from the masks, cut them up and incorporated them into ordinary Portland cement, the most used type globally and the basic ingredient for concrete, mortar and grout.

According to the team, 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 microfibres absorb or dissipate the fracture energy that would contribute to tiny cracks in the concrete. Without these fibres, the microscopic cracks would eventually lead to wider cracks and the material’s failure.

Researchers are conducting more studies to test their idea that the graphene oxide-treated microfibres could also improve durability of the concrete and protect it from frost damage and de-icing chemicals used on roads. They also envision applying the technology to recycling of other polymer materials such as discarded clothing.

The work, led by WSU graduate student Zhipeng Li, was funded through the US Department of Transportation’s National Center for Transportation Infrastructure Durability and Life Extension.