Crushed stone aggregate used to make concrete. Image by Emadrazo
A necessity through the height of the pandemic, face masks are also a source of plastic pollution. To address this, Washington State University has explored a new use for single-use face masks. This is in the form of an additive to concrete, designed to recycle masks and to strengthen the base material.
Research demonstrates that cement mixtures that used mask materials are almost 50 percent stronger than standard mixtures. In addition, the resultant mixture should also be more durable to weathering and structural damage.
Commenting on the research, lead researcher Xianming Shi tells Laboratory News: “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?’”
Production of cement is a carbon-intensive process, responsible for as much as eight percent of carbon emissions worldwide. Current manufacturing methods sometimes involve the addition of microfibers to cement concrete in order to strengthen it. The use of these particles adds considerably to the material cost.
The use of mask material offers an alternative source of fibrous material. An added advantage is that concrete enhanced by mask material 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.
The fibres within masks represent the core materials used – polypropylene or polyester fabrics for the core part of the mask coupled with an ultra-fine polypropylene fibre for the filtering layers.
To test out the suitability of mask plastics, scientists developed a process to fabricate tiny mask fibres, ranging from five to 30 millimetres in length. These were next added to cement concrete to strengthen it and to prevent its cracking.
For their testing, the metal and cotton loops were removed from the masks, prior to the fibres being added to Portland cement (a fine powder, produced by heating limestone and clay minerals in a kiln). This cement is the basic ingredient for concrete, mortar, and grout. The mask microfibers were first mixed into a solution of graphene oxide, which provided an ultrathin layer that strongly adhered to the fibre surfaces (this process improved the interfacial transition zone between mask fibres and cement paste matrix). The microfibers function to absorb the fracture energy that would contribute to tiny cracks in the concrete.
The research is next examining whether graphene oxide-treated microfibers can improve the durability of the concrete and protect it from frost damage.
The research appears in the journal Materials Letters, titled “Upcycling waste mask PP microfibers in Portland cement paste: Surface treatment by graphene oxide.”