Most concrete from demolished buildings is simply dumped, much of it illegally. But there’s a better way – and it involves lightning

Concrete chokes our landfill sites – but where else can it go?

Concrete chokes our landfill sites – but where else can it go?

At the Shenzhen dump, huge shards of dusty concrete lie in imposing piles. Once the very foundation of this Chinese city, these blocks now seem grotesque in their magnitude, and unsettling in their utter uselessness. Jumbled up with the other relics of modern construction – bricks, wood and steel – and dotted with plastic bags and bottles, it could take centuries, even millennia, for Shenzhen’s discarded concrete to disintegrate back into sand.

China produces more construction waste than any other country - around 2 billion tonnes per year (pdf), or around 4kg per person per day. Two million tonnes of this is concrete. In Shenzhen, which has grown from a town with 30,000 residents to a megacity with 11 million in just 35 years, a full 84% of that construction waste is unceremoniously dumped. It doesn’t even all make its way to official landfills, which don’t have the capacity to handle it, so almost half is disposed in unlicensed sites, or illegally tipped.

Q&A What is Guardian concrete week? Show Hide This week Guardian Cities investigates the shocking impact of concrete on the planet, to learn what we can do to bring about a less grey world. Our species is addicted to concrete. We use more of it than anything else except water. Like that other manmade wonder material, plastic, concrete transformed construction and advanced human health. But, as with plastic, we are only now waking up to its dangers. Concrete causes up to 8% of global CO2 emissions; if it were a country it would be the world's worst culprit after the US and China. It fills our rubbish dumps, overheats our cities, causes floods that kills thousands of people – and fundamentally changes our relationship to the planet. Can we kick our addiction, when it's so hard to imagine modern life without it? In this series of articles, Concrete Week will explore the impact of the material on our environment and us, and look at alternative options for the future. Chris Michael, Cities editor



As our world urbanises at a pace never before seen, with buildings rising and falling in as little as 30 years, the crumbled debris of our cities often ends up in landfill. Around 10bn tonnes (pdf) of concrete are manufactured each year: a staggering one cubic metre for every person on Earth. Over the next 40 years the world is expected to build 230 billion square metres in new construction, adding the equivalent of Paris to the planet every single week.

Much of that new construction means knocking down old structures, and gradually engineers and policymakers are waking up to a question: what should we do with our concrete when we’re finished with it?

Facebook Twitter Pinterest China produces more construction waste than any other country. Photograph: Philippe Lopez/AFP/Getty Images

The problem is particularly thorny in the developing world, where there are often limited systems in place to join the dots between demolition and new building projects. In Brazil, one of the biggest emerging economies, recycling is close to non-existent: less than 1% of Brazil’s concrete waste is recycled, according to the Brazilian Association for the Recycling of Construction Waste (Abrecon). About half of Brazilian municipalities send their demolition waste directly to landfills. Many just dump it illegally.

“If [construction] rubbish isn’t collected it has serious ramifications for the public’s health,” said Levi Torres, coordinator of Abrecon. “Many have been taken to hospital because of diseases such as dengue and leptospirosis caused by untreated, dumped rubble.”

Facebook Twitter Pinterest Aguazinha landfill in Olinda, Brazil. Less than 1% of Brazil’s concrete waste is recycled. Photograph: Sipa USA/Rex/Shutterstock

Landfill isn’t the only problem. There is a glaring need for us to drastically limit the production of new concrete and cement, which generates huge amounts of CO2, by recycling components we already have.

The extent to which we are recycling varies wildly between different countries in the world, from around 10% in China to 90% in Japan.

Concrete is tipping us into climate catastrophe. It's payback time Read more

In most developed countries, including much of western Europe, the majority of demolished concrete is put to some use – but mostly to make low-value products like filling for roads. This process is known as “downcycling”. Many researchers and engineers are searching for ways to “upcycle” concrete waste instead, turning old building products into new, first-rate structures and avoiding the need for new or “virgin” concrete.

Recycled concrete can be just as high quality as virgin aggregates at a lower cost – but the barriers are numerous.

Zap it with lightning: how exactly do you recycle concrete?

First there is the technical challenge of separating concrete into its constituent parts. The chief hurdle is to get the aggregate away from other contaminants, including the “rebar” – the bars of reinforced steel that almost all concrete now contains.

One lab in Germany has developed a bizarre but very effective solution: zap concrete with lightning while it’s immersed in water.

Lightning only tends to travel through water and air. It doesn’t like the density of solid objects. However, in 2012, researchers at the Concrete Technology Group in Holzkirchen, Germany, using a high voltage fragmentation system designed and manufactured by the Swiss company SelFrag (SelectiveFragmentation), found that extremely short durations of lightning, 500 nanoseconds, can shoot through water and directly into a solid mass.

On striking concrete, the lightning actually travels between the different components – aggregate, cement, steel – and separates them.

Facebook Twitter Pinterest Researchers in Holzkirchen revived a 1940s Russian method, electrodynamic fragmentation, that allows concrete to be broken into aggregate and cement stone Photograph: Fraunhofer IBP

Other researchers have tried to be more holistic: demolishing with building in mind and building with demolition in mind.

The key problem here is that, once poured, it’s more or less impossible to know what’s inside concrete. Unlike steel, which is stamped and can therefore be traced back to its factory of origin to determine the exact makeup of the alloy, concrete is a grey box.

It has been proposed that each piece of concrete in a building have its own “material passport” – so at the time of demolition, the passport can be used to find the concrete (or, indeed, other materials) a new home.

“One of the biggest obstacles to a circular economy is that we’re not building things for multiple life cycles,” said Eva Gladek, founder and CEO of the NGO Metabolic. “We need to start designing buildings for disassembly.”

Metabolic has been working with municipalities to instigate “circular economies”, by decreasing waste and promoting reuse. Last year they conducted a report for Charlotte, North Carolina, outlining ways the city could reduce waste streams. They found that around 50,000 tonnes of concrete ended up in the city’s landfill each year, and the rest was simply downcycled. They proposed a new system, whereby all waste concrete would be crushed and transformed into new products for construction. According to their calculation, it would even make money: based on selling recycled concrete aggregate to concrete producers at about 80% of the price of virgin materials, the project would generate a revenue of $6.14m annually while costing just $4m.

Facebook Twitter Pinterest 3D printed houses with recycled concrete material. Cities can generate revenue by ‘upcycling’ concrete Photograph: Matjaz Tancic/Alamy

Recycled concrete’s bad rep

It’s not just about cost, unfortunately. It’s also about trust – or distrust, in the case of recycled concrete.

“It’s an image problem,” said Christian Glock, a professor of concrete and masonry at the University of Technology Kaiserslauternin Germany. “The construction industry wants to use the very best possible concrete – even though recycled concrete would work just as well.”

Glock is working on a cross-border research project, SeRaMCo, to develop prefabricated recycled concrete products such as walls, ceilings, benches and skate parks, and launch them in markets across northern Europe.

Facebook Twitter Pinterest The chief hurdle to recycling is to separate the aggregate from the “rebar” – the ubiquitous bars of reinforced steel. Photograph: Frans Blok/Alamy

“We want to show stakeholders that recycled concrete isn’t second rate, it’s really cool,” he said.

In 2008, the EU set a target for 70% of construction waste to be recycled by 2020. Nonetheless, there is a huge disparity in recycling rates: some member states (Netherlands, Luxembourg, Italy, Slovenia, Austria, and Latvia) recycle more than 90%, others under 10% (Finland, Greece and Cyprus). If downcycling is excluded, not a single country reaches the 70% target.

The price you pay

Another problem is that primary materials are so cheap that they’re overused. One of the great flaws of free market pricing mechanisms is that external costs, such as CO2 emissions generated by the cement industry, are not factored into the price of products. There’s simply little market incentive to use it sparingly and efficiently. This is as true for airplane tickets and meat as it is for concrete.

“In today’s conditions, it is more cost-effective to demolish buildings and start again from scratch, than it is to repair a building using recycled concrete,” said Glock. “The market is failing us because it doesn’t incorporate the price of environmental destruction.”

Concrete: the most destructive material on Earth Read more

The UK, for example, continues to produce vast amounts of virgin concrete each year. Recycled aggregate makes up less than a third of new-builds.

“To increase how much new build uses recycled aggregates, we can only build less,” said Andrew Minson, sustainable construction director at the Global Cement and Concrete Association (GCCA). “You can hardly expect an industry of its own volition to decide to produce less if the rest of society isn’t giving two hoots about sustainability.”

To Minson, the biggest priority in the developed world is ensuring that concrete structures are not unnecessarily demolished, but reused and repurposed.

Facebook Twitter Pinterest Construction sites are required to control dust to improve air quality in China. Stronger regulation around recycling concrete is needed globally. Photograph: Reuters

Use less, recycle more

Construction and engineering specialists are more moderate in their approach to concrete than you might believe. Although they tend to share an appreciation for all that concrete has allowed humanity to achieve – frequently pointing out that the modern city would be unthinkable without it – they are, nonetheless, fairly unified in the view that we need to be using much less of it. Particularly virgin concrete.

They agree, too, that this cannot happen without oversight: fines for dumping concrete waste, stronger regulation around recycled aggregate in new builds, and high quality waste management facilities.

Meanwhile, recycled concrete needs a new PR push, to convince the sceptics – and to give rubble a new name.

This article was amended on 1 March 2019 to add more context to a quotation from Andrew Minson

This article was amended on 5 March 2019 to clarify the involvement of SelFrag equipment during the experiments into concrete fragmentation by the Concrete Technology Group

Guardian Concrete Week investigates the shocking impact of concrete on the modern world. Follow Guardian Cities on Twitter, Facebook and Instagram and use the hashtag #GuardianConcreteWeek to join the discussion or sign up for our weekly newsletter