A sustainable approach on the utilisation of COVID-19 plastic based isolation gowns in structural concrete

Why does this study matter?
We already had a problem with plastic waste, and the materials used for hospital-grade PPE, like isolation gowns is made of polyethylene and polypropylene. Polyethylene and polypropylene account for more than 50% of total plastic use. These plastics are incredibly stable, meaning they don’t decompose easily. Pre pandemic, an estimated 2% of plastic-based waste was mismanaged via littering, but recent research shows that COVID-19 triggered an astounding global use of 129 billion face masks and 65 billion gloves every month, causing a drastic increase of plastic production.

We’ve all seen these items in parking lots, walking trails, everywhere! In healthcare, it’s been estimated that hospitals alone are producing about 6 x more plastic-based medical waste than in pre-pandemic conditions. How are we supposed to manage this stuff?

How was the study done?
In this study, the research team shredded isolation gowns that were 55% polypropylene and 45% polyethylene to use as an additive to concrete mixes. Before the isolation gowns were used in the experiment, they were left in an airtight container and quarantined for 96 hours before they were washed, dried, and then shredded. The shreds were added to the concrete aggregates at 0.01%, 0.02%, and 0.03% of the volume of concrete. The control sample had none.

The concrete was poured in molds, just like what is used in testing concrete for foundations for any building. Structural properties were tested for compression, elastic modulus, and flexural strength through a series of experiments. The cores were evaluated with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to analyze bond performance. Ultrasonic Pulse Velocity (UPV) was used testing to evaluate voids and cracks. Structural measures were conducted at 7 and 28 days of curing, again, also an industry standard.

What do we learn from the study?
The SEM-EDS analysis showed an exceptional bond with no gaps. The UPV results found an overall improved quality of the concrete with limited microcracks. For all of you architects who slept through structures class, or just can’t remember because it was so long ago, this is a little bit of a refresher!

For compressive strength (think crushing), the shredded isolation gowns increased the compressive strength with all mix designs. The addition of 0.03% mix led to an increase of 15.5% compared to that of the control samples, which is linked to the UPV results. Flexural strength properties (bending under load) benefitted from the shredded isolation gowns by helping improve the crack bridging effect under stress. There was an increase in flexural strength of nearly 21% at the 28-day test. The concrete mixes also showed increases in the elastic modulus compared to the control mix at rates up to 11.73% for the 0.03% mix.

Can we say the results are definitive?
A key challenge for adopting use of PPE waste in construction would be a steady supply of this waste material and a suitable process for decontamination. This was done in a lab, where the decontamination and mix process could be closely controlled. The real-world application would probably be a just a little more complicated in implementation. Additionally, the authors note that we would need long-term mechanical and durability studies before it can be fully accepted by the construction industry. We’re certainly not going to start using this in building foundations tomorrow. The authors also point out that they only tested one shred size and the effect of different sizes of shreds on the results should investigated.

What’s the takeaway?
This study found that PPE medical waste has the potential to be used as a secondary reinforcement material in structural concrete. Maybe we have a better way of getting rid of this stuff besides the traditional landfill or incinerator. Plastic fibers reportedly can also have sustainability benefits when compared to steel reinforcement. And it’s not just gown from this study. This same team looked at single-use face masks in concrete production, as well as in pavement. While this doesn’t fit into our typical “feature to outcome” format, I was fascinated that the team came up with this idea and offered a new way to think about sustainability.

Who knew?

Summary of:
Kilmartin-Lynch, S., Roychand, R., Saberian, M., Li, J., Zhang, G., & Setunge, S. (2022). A sustainable approach on the utilisation of COVID-19 plastic based isolation gowns in structural concrete. Case Studies in Construction Materials, 17, e01408. https://doi.org/10.1016/j.cscm.2022.e01408

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