Each month the Elsevier Atlas Award recognizes research that could significantly impact people's lives around the world.
Performance of structural concrete with recycled plastic waste as a partial replacement for sand
J. Thorneycroft, J. Orr, P. Savoikar, R. J. Ball
Construction and Building Materials, Volume 161, 10 February 2018, Pages 63-69
Walk down a street and you’ll likely be surrounded by concrete: it’s in the foundations of the buildings and in their walls, in the bridge up ahead and in the path under your feet. Every year, 1.9 cubic meters of concrete are made for every person on the planet – that’s enough to build a 20x20 meter wall all around the equator every year. But there’s a big problem: in some places, we’re running out of sand to make it with.
We are using sand more quickly than it’s being replaced, especially in certain countries, like India. This causes all sorts of problems: if you remove too much sand, bridges might become unstable and be washed away, coastal flooding can threaten communities and fisheries can be affected, not to mention the impact on wildlife.
What if there was a way to reduce the amount of sand we’re using to make concrete, without having to stop making it? That’s what Dr. John Orr, University Lecturer in Concrete Structures and EPSRC Early Career Fellow in the Department of Engineering at the University of Cambridge in the UK, has been investigating, and he’s come up with an approach that solves another big problem – plastic waste.
In his Atlas Award-winning paper in Construction and Building Materials, Dr. Orr and his colleagues, Dr. Purnanand Savoikar from Goa Engineering College, and Dr. Richard Ball and James Thorneycroft from the University of Bath, show it’s possible to replace 10 percent of the sand in concrete with plastic, with only a small impact on the material’s strength.
“It is really a viable material for use in some areas of construction that might help us to tackle issues of not being able to recycle the plastic and meeting a demand for sand,” he said.
In India, the sand shortage is becoming a serious problem. “Because there was such a huge demand for sand in India, legitimate sources weren't providing enough capacity,” said Dr. Orr. “Some people turned to illegal dredging, which causes environmental problems.” A 2011 high court ruling saw the end to dredging – a ban that has driven up the cost of sand and reduced its availability.
But the lack of supply doesn’t stop the demand. India has one of the world’s fastest-growing economies and rapidly growing urban population, and therefore a high demand for concrete with which to build urban housing and other buildings; in 2014, 280 megatons of cement was manufactured there.
That same year, Dr. Orr’s colleagues at the Goa Engineering College presented him with two problems to solve: the sand shortage and India’s lack of plastic recycling. The answer lay in combining the two.
In India, 15,000 tons of plastic is being dumped in the streets every day because there are very few suitable recycling facilities. Previous research had explored partially replacing the sand in concrete with crushed car tires and other materials, so Dr. Orr and his team decided to try the approach with different types of plastic waste. He explained:
“Typically, when you put an inert, man-made material like plastic into concrete, you lose a bit of strength because the plastic material doesn't bond to the cement paste in the material in the same way that a sand particle would. So the key challenge here was to have a limit between a small reduction in strengths, which we achieved, and using an appropriate amount of plastic to make it worthwhile.”
What they ended up with was 10 percent replacement of the sand. That might not sound much, but it would add up to a saving of 820 million tons of sand every year. There is still more research to be done, to understand the behavior of the new material when it’s exposed to fire, for example, but it is certainly a promising proof of concept.
The research is part of a bigger effort to reduce the environmental impact of our buildings. Dr. Orr and his team also work on reducing the amount of concrete needed overall. “If we went back 2,000 years, the way that Romans made concrete isn't all that different than what we do today,” he said. “Really, we haven't yet capitalized on the fact that the material is fluid, the fact that we can make all sorts of interesting shapes, and that untapped potential might help us to save 50 percent of the concrete, which means less CO2, which means less impact on the environment.”
A conversation with Dr. John Orr
In this podcast Dr. John Orr talks about the problem with our extreme use of concrete, and how using plastic in place of some of the sand can help solve India’s plastic waste problem.Listen now.
What's the problem with using sand in concrete?
In countries like India where there is such a huge amount of construction – much, much more than we would see in the UK – there is essentially a problem with over-dredging. We love concrete, it’s our favorite construction material. We use about 1.9 cubic meters of concrete per person, per year on the planet, and about 30 percent of that is sand. In a country like India where there’s rapid growth of cities, people need places to live and work; that requires lots of concrete, which puts a lot of pressure on sources of sand.
What kind of plastics could be used to replace the sand? And what impact will that have on waste?
In India, there’s about 15,000 tons of waste plastic dumped per day, and there's very little recycling; you will often see lots of plastic waste on the streets, in rivers and so on. We started by saying, can we take waste plastic bags and bottles, and in some way shred them into small pieces which could be put into a concrete mix in a small percentage? What we ended up with is a structural concrete, strong enough to be used in a foundation, a ground floor slab or a column in a building, but we took 10 percent of the sand out and replaced it with shredded up plastic. We tried 10 different types of plastics and settled on one that gave us the best performance: plastic bottle material ground into a shape and size that is very similar to sand.
What makes plastic waste a good replacement for sand?
Well, in many respects, it's not a good replacement. Typically, when you put an inert, man-made material like plastic into concrete, you lose a bit of strength because the plastic material doesn't bond to the cement paste in the material in the same way that a sand particle would. So the key challenge here was to have a limit between a small reduction in strengths, which we achieved, and using an appropriate amount of plastic to make it worthwhile. We settled on 10 percent replacement. If you did that with all the concrete that we make, that's 820 million tons of sand saved every year, which is not an insignificant amount.
Does using plastic in place of sand change the impact concrete production has on the environment?
Concrete has a huge environmental impact; cement alone is about five percent of global CO2 emissions – that has a huge impact on the environment. In my research group, our work is dedicated to what we call light-weighting, which is essentially using less material to do the job that we need to do. We can do all sorts of things to buildings to make them more efficient, and part of that is just using less materials.
The environmental problem with the sand is really when we get over-dredging. As you start to take away lots and lots of sand from the mangroves, then you lead to degradation of the root systems, animals suffer, the wildlife suffers, the plants suffer. In Europe, everything very carefully controlled; in India, the big problem, which led to the Supreme Court banning all dredging of sand because the damage was so great, was simply that it was being done illegally.
You mentioned there's a way of reducing the amount of sand needed. Can you tell us about that?
Concrete is about 30% sand, so one solution we're exploring in other research is simply to use less concrete. Our research has shown that concrete structures might be 30, 40, or 50 percent inefficient. What that means is we could take out 40 percent of the material and have the same performance. If we cut our concrete use in half, then as a result of that, we're also cutting our sand consumption in half.
We know that we have a huge amount of construction that's going to happen in the next 40 years: 230 billion square meters of buildings are going to be put up, that's equivalent to building Paris every week. What we really need to do is use the research that we're doing in my group and with others to help ensure that we don't repeat these mistakes of really quite inefficient buildings.
What still needs to be done before this method is put into use, and do you think it will be?
In a country like India where there is this dual challenge of lots of waste plastic and lots of concrete construction, it could be used quite easily – all you need to do is pour some plastic into your concrete mix and then mix it as you would normally. It could be used in a ground-bearing floor slab or a footing or a small house, that kind of scale; I think that people would be more wary of using it in a high-rise building, simply because it's an unknown material. What we need is really demonstration: prototype buildings, for example, showing the material looks the same, feels the same, performs the same, in terms of what we would expect concrete to do.
What the Advisory Board said
“Intriguing approach for tackling down the two gigantic environmental issues of this era---plastic waste and sand dredging. Reducing plastic waste is ideal, however, this kind of innovative concept is scientifically intriguing. A whole world will be curious about further investigations.” – Ryoji Noritake
“From a horizon-scanning perspective, global governance of sand resources, including sustainable consumption and production mechanisms is going to be an important emerging issue in the coming years.” – Louise Gallagher
“There were several studies about ecological consideration in the selection this month. This one is not only one of the most promising but also one of the most understandable for a non-initiated audience. The aim is rather clear and straightforward. The general underlying ambition very relevant nowadays.” – Emmanuel Baron
“The paper proposes innovative and practical solution for solving two important global environmental problems.” – Osamu Saito
“Plastic waste is such a pervasive problem, and identifying new uses for recycled material is essential. At the same time, there is need for environmentally friendly concrete alternatives, including in developing countries. If costs of this approach can be reduced, it could be transformative for developing economies.” – Temina Madon
Find out more:
- Documentary, Sand Wars
- TEDxBarcelona talk by the maker, Denis Delestrac
- BBC Radio 4 program, The End of Sand
- John Orr’s Webpage
Construction and Building Materials
Construction and Building Materials publishes research on construction and building materials and their application in new works and repair practice. The journal features papers on laboratory and numerical investigations as well as full-scale projects. The materials and technology covered include cement, concrete reinforcement, ceramics, timber, steel and polymers.
Science impacts everyone's world. With over 2,500 journals publishing articles from across science, technology and health, our mission is to share some of the stories that matter. Each month Atlas showcases research that could significantly impact people's lives around the world or has already done so. We hope that bringing wider attention to this research will go some way to ensuring its successful implementation.
With so many worthy articles published the tough job of selecting a single article to be awarded "The Atlas" each month comes down to an Advisory Board. The winning research is presented alongside interviews, expert opinions, multimedia and much more on the Atlas website.
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