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 using mask materials was 47 per cent stronger than commonly used cement after a month of curing.
Production of cement is a carbon-intensive process, responsible for as much as eight per cent 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 for the ecosystem, according to a press release by the Washington State University.
In their proof-of-concept work, 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 to 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 microfibres 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.
Zhipeng Li, a graduate student in WSU’s Department of Civil and Environmental Engineering, led the work, which was funded through the U.S. Department of Transportation’s National Centre for Transportation Infrastructure Durability and Life Extension.
“These waste masks actually could be a valuable commodity if you process them properly. 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? This work showcases one technology to divert the used masks from the waste stream to a high-value application,” Xianming Shi, professor and interim chair of the department of civil and environmental engineering and the corresponding author on the paper, said in a statement.