Discarded PPE makes concrete stronger

Researchers at Royal Melbourne Institute of Technology School of Engineering have found that disposable personal protective equipment can be used as reinforcement materials in making structural concrete.

Their studies, which followed earlier work on the recycling of used rubber tires, demonstrated that using shredded PPE – discarded isolation gowns, masks, and nitrile gloves – could increase the strength of concrete by 22% and improve its resistance to cracking.

The RMIT team is believed to be the first to investigate the feasibility of recycling PPE into concrete, a practice that could combat the wasteful aftereffects of the COVID-19 pandemic.

Since the start of the pandemic, an estimated 54,000 metric tons of PPE waste has been produced on average globally each day, according to the researchers. In Africa alone, the daily use of face masks exceeds 586 million. In 2020, the United States produced an entire year's worth of medical waste in two months.

And 129 billion disposable single-use face masks are used and discarded around the world every month, with millions being discharged into the environment, washing up on beaches, floating beneath oceans and ending up in vulnerable places.

The global pandemic has not only affected the economy and health of the world's population but is now seriously threatening the natural environment. The main plastic in single-use face masks is polypropylene, which in a landfill can take more than 25 years to break down, according to the researchers.

They also noted that polypropylene is a thermoplastic polymer, which turns into microplastics when it ends up in our waterways, impacting delicate ecosystems and potentially ending up in our food sources.

Thus, the effects of the global pandemic are not only severely impacting the world economy but also will continue to impact day-to-day lives long after the pandemic has ended.

Use of plastic fibers in concrete has attracted attention from the construction industry and academia for some time as plastic fibers hold many sustainability benefits when compared to steel reinforcement, the researchers observed.

Polypropylene fibers are widely used throughout the concrete industry due to their mechanical properties such as tensile strength as well as their ease of production, and high alkaline resistance

"We urgently need smart solutions for the ever-growing pile of COVID-19 generated waste – this challenge will remain even after the pandemic is over," said Shannon Gilmartin-Lynch, RMIT vice-chancellor's Indigenous pre-Doctoral Fellow and first author of the team's research papers.

"Our research found that incorporating the right amount of shredded PPE could improve the strength and durability of concrete," he explained.

In three separate feasibility studies, disposable face masks, rubber gloves and isolation gowns were first shredded and then incorporated into concrete at various volumes, between 0.1%and 0.25%.

The researchers found:

• Rubber gloves increased compressive strength by up to 22%.

• Isolation gowns increased resistance to bending stress by up to 21%, compressive strength by 15%, and elasticity by 12%.

• Face masks increased compressive strength by up to 17%.

The studies were published in recent editions of the journals: Case Studies in Construction Materials (December 2022), Science of the Total Environment (January 2022), and Journal of Cleaner Production (May 10, 2021).

In the most recent study, the researchers observed the effects of adding shredded isolation gowns to aggregates at 0.01%, 0.02%, and 0.03% of the volume of concrete. The effects of the various concentrations of shredded plastic gowns on the mechanical properties of the concrete were investigated through a series of experiments and analyses.

The results demonstrated an enhanced bridging effect between the cement matrix and shredded isolation gowns, allowing for a steady trend of improved mechanical properties with increases of 15.5%, 20.6%, and 11.73% across compressive strength, flexural strength, and the modulus of elasticity, respectively.

Rajeev Roychand, Ph. D., joint lead author of the studies, said there is potential for construction industries to play a significant role in transforming this waste into a valuable resource.

"While our research is in the early stages, these promising initial findings are an important step towards the development of effective recycling systems to keep disposable PPE waste out of landfill," he said.

Corresponding author and research team leader Professor Jie Li, Ph. D., said PPE waste is significantly impacting the environment.

"We have all seen disposable masks littering our streets, but even when this waste is disposed of properly, it all ends up in landfill," Li said.

"With a circular economy approach, we could keep that waste out of landfill, while squeezing the full value out of these materials to create better products – it's a win on all fronts."

Next, the team will evaluate the potential of mixing PPE streams, develop implementation strategies and work towards field trials.

The RMIT team is eager to collaborate with the healthcare and construction industries to further develop the research.

Casafico Pty Ltd., a leading manufacturer of building materials in Australia, has partnered with the RMIT scientists to use their research findings in a field project.