How waste plastic can replace sand in structural concrete?

A joint research conducted by India and the UK has shown that waste plastic can be a viable partial replacement for sand in structural concrete, providing a possible solution for sustainable construction work in India.

The research, conducted by the University of Bath in partnership with Goa Engineering College, has shown how replacing 10 percent of sand in concrete with waste plastic may help to reduce the vast amounts of plastic waste on Indian streets and deal with the country's sand shortage.

"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,” explains Dr. John Orr, the principal investigator and Cambridge University lecturer in Concrete Structures -- who completed the research during his time at the University of Bath.

"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. 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.

The study was published in the journal 'Construction and Building Materials' earlier this month and was selected by an international scientific committee to receive the Atlas Award in recognition of its potential societal impact around the world.

The research team investigated various different types of plastic to see if they could be crushed and used as a replacement for sand, which typically accounts for 30 percent of a concrete mixture.

The study, titled 'Performance of structural concrete with recycled plastic waste as a partial replacement for sand', provides the proof of concept for an approach which could significantly address India's waste and sand shortage problems as well offering a solution for future sustainable construction.

"Characteristics of the waste being added to the concrete, such as the type of plastic and the size and shape of the particles can all have an influence on the final concrete properties. Even when the reduction in performance prohibits structural applications lower tech uses such as paving slabs may be viable," said Dr. Richard Ball, co-investigator and Reader in the University of Bath's Department of Architecture and Civil Engineering.

The project showed that replacing sand with similarly sized and shaped waste plastic particles from the ground up plastic bottles resulted in concrete which was almost as strong as conventional concrete mixtures.

As per the research's calculation, replacing 10 percent of sand in concrete could save 820 million tonnes of sand a year and help reduce levels of plastic waste.

The researchers investigated this approach by testing concrete cubes and cylinders. Five types of plastic particles, including those from recycled plastic bottles and recycled plastic bags, were trialed in the mixes in a variety of sizes. Recycled plastic bottles, ground and graded to match the sand being replaced, were found to perform best.

As one of the world's fastest-growing economies, a booming construction sector and a rapidly growing urban population, the cost and demand for sand in India has sky-rocketed with 280 megatons of cement manufactured there in 2014 alone, the study noted.

This has led to unregulated sand extraction from riverbeds to the extent that such mining is now banned in many Indian states.

Also, the high level of sand extraction can lead to other problems such as coastal erosion and an unstable fishing industry.

The study noted that India's country's rapid development has also meant waste plastic, which has become a significant problem in the country with 15,000 tons of plastic dumped in the streets every day due to a lack of suitable recycling facilities.

Globally, concrete plays an integral part in the construction industry accounting for around 9 percent of a new building's budget while being responsible for nearly half a building's CO2 emissions.

Each year, 4.2 trillion kilograms of cement is manufactured, resulting in about 1.9 cubic meters of concrete for every person on the planet.

The research was funded by the British Council under the UK India Education and Research Initiative (UKIERI) programme established in 2006 to foster greater educational links between the countries, including knowledge sharing and student mobility.

Besides Orr and Ball, the others on the research team included James Thorneycroft from the University of Bath and Professor Purnanand Savoikar from Goa Engineering College.