Research from Bath University has demonstrated that some of the sand used in concrete can be swapped out for waste plastic, potentially leading to more sustainable construction.
The study, conducted in partnership with India’s Goa Engineering College, was prompted by India’s booming construction sector and a sand shortage the country is enduring as a result. It’s estimated more than 20 billion tons of concrete are produced globally each year, making it the world’s second most consumed substance after fresh water. Sand typically comprises 30 per cent of any concrete mixture. By replacing 10 per cent of that sand with finely ground plastic particles, the Bath team estimates that over 800 million tonnes of sand could be saved.
Published in the journal Construction and Building Materials, the research explored the impact of five finely graded plastics on the structural strength of concrete tubes and cylinders. It was found that sand-sized PET particles from recycled plastic bottles provided the best results, achieving a target compressive strength of 54 MPa, similar to that of structural concrete.
“The research was focused on adding enough plastic so as to make the additions worthwhile in terms of providing a use for the waste, but at the same time not so much as to reduce the concrete strength to an extent which makes it too weak for structural applications,” Dr Richard Ball, from Bath’s Department of Architecture & Civil Engineering, told The Engineer. “10 per cent by volume additions of plastic could save 820 million tonnes of sand every year from being used in concrete mixes.”
“Properties such as the type of plastic and the particle size and shape will all have an influence on the strength of the concrete to which it is added. If we can identify the most favourable properties of the ‘plastic sand’ we may be able to increase the additions allowable without compromising the properties. There are also important factors such as the rheology of the wet mix, environmental durability and fire performance which can be further explored.”
Where the strength of the concrete is compromised, Ball says there are still plenty of applications where it can be useful.
“Even when the reduction in performance prohibits structural applications lower tech uses such as paving slabs may be viable,” he said.
According to principal investigator Dr John Orr, introducing synthetics like plastic into concrete generally weakens the material, as plastic doesn’t bond to the cement mix like sand does. Central to the work was finding the balance between maintaining the concrete’s strength, yet still incorporating enough plastic into the concrete so a significant amount of sand could be saved.
“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,” said Orr, previously of Bath University and now a lecturer in concrete structures at Cambridge. “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.”
The research recently received the Atlas Award for its potential societal impact around the world. While ground up waste plastic was used for the study, Orr told The Engineer that the team is now exploring some novel sources for plastic material that is already graded to the required level.
“The plastic we use in the mixes are by-products of other industrial processes,” he explained. “As an example – the manufacture of plastic optical lenses for glasses produces finely ground plastic waste which would normally be sent to landfill or incinerated. So you could argue there is no extra energy required to then use this material in concrete, we are making use of a waste material from other processes.”
Many years ago, when the USA was engaged in what was then ‘billed’ as an anti-Comm***st action in Asia, a vast base as built (Cam Rann Bay) Amazingly, they had to import sand from elsewhere, as that available locally would not ‘bind’ with the cement used, to manufacture concrete. The Gods were clearly against the effort, right from the start! My then US employer was also tasked with developing processes and facilities to increase 5 fold the processing of acrylic fibres: the local bugs just loved eating jute, the traditional material for sand-bags!
I think one problem I’d have with that is that the concrete presumably doesn’t last forever and then how do you recycle it so as not to let fine grained plastic out everywhere ? In e.g. 50 years or whatever will there be a problem?
It will just be recycled again including the concrete as secondary aggregates .
But why???
The point shouldn’t be to replace sand with plastic, which actually provides a performance detriment, while still producing new plastic to replace the “recycled” stuff.
We need to replace plastic with plastic so we can produce less plastic in the first place, which is a far larger problem (oil consumption) than space in landfill.
Also the fact of this idea probably ending up with more plastic particles in water streams. Seems like these resources would be better spent on a different project or looking at how performance benefits could be achieved from using this waste plastic.
How about using the plastic sand in geotubes for coastal erosion prevention? A vast volume of the material would thus be used. In my area of western Washington State I’ve proposed a geotube solution to help reduce tsunami flooding.
An interesting study.
Instead of plastic bottles, the use of pieces of polythene bags – which may work as fibrous materials to check tension cracks – may prove beneficial.
Do we want plastics in the structure of buildings? Is this safe for our health? And, if the building is demolished?
Can’t we just put the bottles through a grinder and use the unwashed pieces to replace some of the stones, not sand? A lot of concrete is used building roads (under the asphalt). Don’t grind it too fine when it would be hard to control, we don’t want it to end up in our waterways.
If you heat the plastic and mix the waxy melted material with the plastic it actually improves the quality of the concrete mix and can be used in larger ratios, according to this study check out page five http://www.ijoser.org/Files/1401.pdf
Does anyone know if commercially plastic is being used as a mix with concrete? If not I am looking for a company to do some trials with large quantities of regular 1-5mm granulated flexible plastic at zero cost ex.works.
Hi Alistair, the Concrete Technology Unit at The University of Dundee who might be able to test this if you are still interested?
i think it’s a great idea using a small ratio of ground plastic in concrete
and saving millions of tonnes a year in sand……i also think hard plastic smelted down and reformed in a way of type 1 and mixed in with crushed concrete …could be another use for it
Why not utilize Cleaned “Fly Ash” which is Pozzolanic and can be a substitute for sand and reduction of Portland Cement. The Romans use Pozzolans in their cements/concretes and they are still around.
Fly Ash can also be treated to sequester any heavy metals and acids with natural absorbents.
The resulting mixes are stronger, lighter, cure in less time and use less water, more corrosion resistant from acids/weathering etc and and can be made with, upto 65% less Portland Cement [reduced carbon emissions in the manufacturing of the Portland Cement per ton]…. everyone wins in the globe climate emissions scenario and the world has billions of tons of Fly Ash at every Coal Fired Power Plant, ever operated and polluting the ground waters, air and soils where dumped/landfilled!
Does not take a genius to see how we can sequester these “Fly Ash” wastes for a beneficial use and use for Infrastructure rebuilding at less cost and still be recyclable in the future!