Recycled mask polypropylene microfibers benefit tensile properties and prevent thermally induced spalling of high-strength engineered cementitious composite (HS-ECC)

Abstract

The COVID-19 pandemic has led to a significant amount of waste medical masks being generated, which if not properly managed would pose a substantial risk to the natural environment. In this context, this study focuses on upcycling the waste medical mask propylene (PP) microfibers in high-strength engineered cementitious composites (HS-ECC) to mitigate its explosive spalling issue upon fire exposure. At ambient temperature, the compressive strength of Ref-ECC (without PP microfibers) reached 96.4 MPa, and the incorporation of recycled mask fibers (RMFs) up to 0.5 vol% had a negligible effect on it. The incorporation of low-cost RMFs benefited the uniaxial tensile properties of HS-ECC. For instance, at 25 °C, the incorporation of 0.5 vol% RMFs increased the tensile strain capacity and tensile strength of the HS-ECC to 2.60% and 7.9 MPa, from those of the Ref-ECC (2.03% and 7.1 MPa), respectively. The 0.5 vol% RMFs in the HS-ECC increased the tensile strain capacity to 3.80% at 60 °C, 4.50% at 90 °C and 5.23% at 120 °C notwithstanding their reduced tensile strength, respectively. The RMFs in the HS-ECC induced inner (sub)micron-sized cracks after thermal exposures, facilitating multi-cracking behavior. After 600 °C/2h heating, severe spalling occurred in the Ref-ECC cylinder specimens, demonstrating that polyethylene (PE) fibers alone (at 1.8 vol%) cannot prevent spalling upon fire exposure. However, the incorporation of RMFs (as little as 0.3 vol%) was proven as an effective preventive measure against the explosive spalling phenomenon in HS-ECC.