Using Fibre recovered from face mask waste to improve printability in 3D concrete printing

Surgical face mask usage has rapidly increased in the last two years due to the COVID-19 pandemic. This generates vast amounts of plastic waste, causing significant risks to the ecosystem. Thus, this study assesses the potential of using recycled fibre from face mask waste as fibre reinforcement in 3D concrete printing (3DCP) applications to improve printability while reducing landfill waste. The effect of recycled fibre from waste face masks on the rheological characteristics of printable mixes and the mechanical performance of printed elements was evaluated for different contents of shredded face masks (i.e., 1% and 2% by vol). The rheological properties like static and dynamic yield strengths, apparent viscosity, and thixotropic behaviour, along with compressive and flexural strength, were evaluated for 3D printed specimens and mechanical properties were compared to their mould-cast counterparts. Further, the variation in the interlayer bond strength and porosity due to different fibre dosages was also investigated. In addition, a comparative study on the fresh and hardened properties was performed for the printable mixes with polypropylene (PP) fibres and face masks. The addition of face masks significantly improved the rheological properties with good extrudability and buildability for all the dosages. Compared to face masks, mixes with PP fibres showed poor extrudability with higher fibre dosages. The compressive strength was increased by 41% for a 1% dosage of face masks when compared to the unreinforced concrete. Furthermore, the flexural strength when tested along the weaker interface, showed an increase of 74% and 82% for the addition of 1% and 2% face mask content. The interlayer bond strength of 1% face mask content showed 21% improvement and was observed to have the highest surface moisture content. The mechanical performance of face masks and PP fibres are observed to be comparable for 1% dosage. The mechanical properties of printed and mould-cast specimens were also observed to be similar.