Ever since I posted the first post on recycled plastic in construction projects like tiles & roads, everyone in close contact wanted to know the side effects of plastic usage in such projects.
The questions targeted micro leaching of plastics, emissions of greenhouse gases. In this post, I am trying to cover related references which will help to answer these questions.
Climate Change and Gaseous Emissions.
Greenhouse gases, such as carbon dioxide, methane, nitrous oxide, and certain synthetic chemicals, trap some of Earth’s outgoing energy, thus keeping the heat in the atmosphere. This heat-trapping is one of the major causes of the increase in heat and global and regional climate changes.
With plastics, I came across one nice article which explains the contribution of plastics to the gaseous emission.
While searching for references, I found that most of the emissions generated in the early phase of the plastic life cycle.
According to Vasudevan et al. (2012) before mixing with bitumen, a 10 to 15% plastic mixture used as an aggregate coating. He conducted practical analysis explaining that using plastic waste helps avoid plastic burning along with solid municipal waste. In the same research paper, noted that for every 1 km of road laid, a ton of plastic waste is used. This should reduce the emissions of carbon dioxide by 3 tonnes.
Most plastics have a softening at around 130–140 0C with no gaseous evolution, so one can easily use the plastics in the flexible pavement, the binding property of the coated aggregate with a higher percentage of plastic shows the compressing strength of nearly 130 tonnes, so, it suggests that PCA has strong adhesion capacity, and also a confirmation of the material to serve as a binder.
Any approach that melts plastics, and does not burn is thus effective in preventing carbon emissions, whether it is tiling, brick making, pavement, concrete blocks, etc. India’s plastic roads have a long history and many countries are following the suite with slight changes in method. This would contribute significantly to reductions in greenhouse emissions.
When considering this element, I would like to add another point, and that is a comparison of conventional road construction practices vs. plastic road construction besides microplastics leaching because of plastic roads.
The integral part of the plastic road is coating the stone and sand aggregates with melted plastic. This coating ensures the plastic does not come into contact with the traffic tires, thus avoiding the release of microplastics. The wear and tear of tires on roads are a significant source of microplastics/particulates. Plastic.au is exploring potential ways to beat this issue at/around the plastic roads.
The patent detail of Prof. R. Vasudevan mentions that the hot aggregates coated in melted plastic added to hot bitumen (which is 8 to 20% less than normal road construction depending upon the quality of plastics saving the amount.)
While working on a post, Prof. R. Vasudevan mentioned that the coating layers ensure that the plastic remains intact and not converts in microplastics.
According to NEERI road dust is the largest contributing factor to the pollution. With plastic roads, this dust reduces significantly.
Here is 110 pages report which covers the complete assessment which compares the traditional road construction methods, and the one using plastic additives. This effort in Ireland sheds light on many aspects. The report covers the longevity of roads, climate change, abrasion, and even covers inventory and transport costs.
Hot mix asphalt concrete is often used as a standard surfacing material for heavy-duty roads. It is a carefully proportioned mixture of coarse aggregates, fine aggregates, mineral fillers if required, and bitumen. The environmental assessment report reveals the toxic nature as compared to plastic roads.
A review by Prof. Kiran Bhoot, Kapil Malviya, Thanvendra K Prajapat mentions the following points.
The cleaning process- Toxics present in the co-mingled plastic waste would start leaching.
During the road laying process- the presence of chlorine will release noxious HCL gas.
After the road laying- according to opinion, the first rain will trigger leaching because the plastics will merely form a sticky layer (mechanical abrasion).
The components of the road, once it has been laid, are not inert.
These are theories with no solid research backing for these points. I tried to search for references and could not find any. Maybe future research could shed some light on these aspects, too.
The usage of recycled plastics has more advantages than disadvantages.
Mitigating the plastic waste problem
The longevity of the construction
Low maintenance costs
Reducing greenhouse gas emissions
Savings on costly bitumen (with roads), (Need to list out materials saved in tile making/ brick making process. Experts can let me know.)
Microplastic leaching (Which I feel is less than the current situation)
Possible Occupational Hazards
One Food for Innovative Idea–
To think about what can be done! Here is the detailed study of the raw materials. Possibly some researchers can take this as a study project in India.
Hope this helps those curious minds to think further…
Follow the blog for another interesting story next week!
Just a little bit of more reading!
Do you know what is the microplastics consumption on an average?
A new study in the journal Environmental Science and Technology says it’s possible that humans may be consuming anywhere from 39,000 to 52,000 microplastics particles a year. With added estimates of how much microplastics might be inhaled, that number is more than 74,000.
A study published in the journal Environmental Science and Technology found microplastics in more than 90% of the packaged food-grade salt—also known as table salt—for sale in stores. India is in the top list of highest microplastics content.