Nigeria doesn’t have enough roads, and it’s making life harder for people, especially in rural areas. The Nigerian government’s latest estimate is that the country needs another 200,000 kilometres of roads and this will cost a whopping N18 trillion (US$12.2 billion).
These new roads will help people get to schools, hospitals and markets, and boost the economy. But the high price of equipment, maintenance, labour and materials needed, like aggregates, bitumen (tar or asphalt) and cement, are putting the new roads out of reach.
Read more: Africa's roads are badly built, and there aren't enough. This can be fixed
Rough terrain, environmental concerns and complicated road designs can make building roads more expensive too. For example, Nigeria has lateritic soil made up of a type of clay. It’s not easy to make lateritic soil stable for road building because the clay makes it prone to swelling and shrinking with changes in moisture levels.
This can cause the soil to become unstable and the roads to deteriorate. This kind of soil also makes it difficult to build and maintain roads that can withstand the weight of large vehicles during the rainy season.
Engineers usually use cement and lime to stabilise soil like this. But these are expensive and bad for the environment because it takes huge amounts of energy to make them. Cement on its own is responsible for 8% of greenhouse gas emissions globally.
Read more: Cement is a big carbon emitter and quality is costly: a civil engineer explains
So engineers have been looking for a substance that can be added to the soil to make roads durable and cheaper.
I am a civil engineer who’s been researching environmentally friendly materials that could be used as substitutes for cement in construction, like coal bottom ash, quarry dust and rice husk ash.
My research team set out to discover if old single-use plastic bottles, instead of cement and lime, could be added to the soil to strengthen it.
In a laboratory, we added shredded plastic waste to soil and conducted geological tests on the lateritised plastic (soil mixed with plastic). We experimented with different amounts of the plastic and found that adding 2% plastic to soil worked best.
At this amount, the soil became denser when compacted and could carry more weight without failing. The soil became more suitable for road construction.
By reducing the need for traditional soil stabilisers like cement and lime, our research could make a real difference in building the 200,000km of roads Nigeria needs, in a way that takes plastic out of garbage dumps and puts it to use in roads.
How we found out that plastic waste might stabilise roads
We simply sieved the soil to remove debris and plants, shredded the plastic bottles, mixed them together and added water to replicate rainfall and moisture from the environment.
We tested the mixture to see how dense it could get when compacted and how strong it was under pressure (this is known as the California Bearing Ratio). We found that plastic acted like a filler and the more plastic we added, the more water was needed to compact the soil.
Plastic also made the soil lighter. The best balance for both density and moisture was at 2% plastic for density and 10% plastic for moisture content. This made a lighter, less dense material which could be useful for building sustainable roads.
California in the US also uses plastic waste in road construction. However, this is different because they use recycled asphalt pavement and liquid plastic to build roads.
What needs to happen next
Our waste plastic-based lateritic soil for road construction has only been tested in a laboratory. It hasn’t been turned into a road that can be tested.
Governments and construction companies now need to fund research and development into the optimal use of plastic waste as a soil strengthener. In practice, this means they should build a new lab or pilot road to test and refine the use of waste plastic in soil improvement for road construction.
Policies and regulations are needed to encourage recycling and reuse of plastic waste in construction projects. The Nigerian government could implement the global extended producer responsibility policy. This holds manufacturers responsible for recycling their products after people have used them.
A regulation that says some of the content in bottles should be recycled, subsidising environment friendly practices and taxing virgin plastics, would also help.
Read more: Concrete versus asphalt for Nigeria's roads: which is better?
Banning single use plastics, certifying recycled products, investing in recycling equipment, and making sure that the government promotes recycled materials can also drive innovation.
Setting up awareness campaigns and giving companies tax credits for recycling will help create a supportive environment for plastic waste recycling and reuse in construction industry.
By embracing this innovative approach, Nigeria can build a greener future while tackling both poor soil quality and the growing problem of plastic waste.
Ifeyinwa Ijeoma Obianyo does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
This article was originally published on The Conversation. Read the original article.
