Researchers from the School of Engineering at RMIT University in Australia have published a study in Science of the Total Environment which proposes the reuse of face masks as a structural component in road base and subbase applications.
The scientists remark that while the public health impact of the COVID-19 pandemic is inescapable, its environmental impact has gone relatively unnoticed. They note while little research has been done, it was estimated that 129 billion face masks were disposed of in June 2020, and this figure is highly unlikely to have declined in the meantime, particularly in light of the fact many governments have since made mask-wearing in public spaces mandatory.
The impact of this dramatic uptick in single-use plastics being deposited into the environment necessitates multidisciplinary collaboration to mitigate, the researchers argue. They suggest that shredded face mask (SFM) material could be used in combination with recycled concrete aggregate (RCA) in pavement constructions, simultaneously reducing waste and satisfying the necessary strength requirements.
Using an SFM RCA mix as a pavement base material could have the dual benefits of reducing pandemic-related waste and reducing construction costs
The test involved fresh face masks (safety restrictions prohibited the use of used masks) shredded to 0.5 cm width and 2 cm length, and subsequently mixed with dry RCA at 1%, 2% and 3% proportions. The materials produced were then characterised by particle size distribution, organic content, particle density, specific gravity, pH, LA abrasion, aggregate crushing value and flakiness, before being tested in terms of strength.
The researchers used the unconfined compression test to determine the relative strength values of the materials. Unconfined compressive strength (UCS) values were compared between a control sample, with 0% SFM, and the three samples with progressively more SFM content. Interestingly, the sample with 1% SFM had a 17% higher UCS value than the control, at 216 kPa compared to the control’s 185 kPA. The researchers say this is because the mask’s fibres “played a reinforcing role in binding the RCA particles,” similar to previously observed results with reinforced soils.
Beyond 1% SFM content, the researchers saw diminishing returns, with the 2% and 3% samples measured at a UCS value of 204 kPA and 178 kPA respectively.
The study concludes that SFM is a viable material to mix with RCA for pavement base and subbase applications, offering an increase in strength and stiffness, in addition to a potential increase in ductility and flexibility owing to the higher tensile strength of the SFM compared to pure RCA particles. It notes the diminishing returns beyond 1% SFM content, however posits that at this ratio, a one kilometre long, two lane-road with a width of 7 m and a thickness of 0.5 m for its base and subbase would use 93.2 tonnes of SFM and prevent three million face masks from going to landfill.
The researchers argue, therefore, that using an SFM RCA mix as a pavement base material could have the dual benefits of reducing pandemic-related waste and reducing construction costs.
