Steel and concrete are climate change’s hard problem. Can we solve it?

steel making

With temperatures reaching 1300 °C, making steel is a hot and dirty business

Wolfram Schroll/Industriefotograf

“DANGER. No unauthorized entry. Hot rolling in progress.” If anything, the sign beneath the dirty hunk of industrial machinery underplays things. When the 11-tonne slab of metal I’ve been watching emerges from the furnace, heated to 1300°C, it glows incandescent white. Then it zips along a conveyor belt, hissing and steaming as it is cooled by water jets, before a line of rolling cylinders press it into the final product: a sheet of gleaming steel.

For all that we live in the digital age, we still rely on hot and dirty processes like this to construct our cities, homes and vehicles. Walking around the steelworks in Newport, UK, I get a sense of the immense energy required – and this is only the stage at which the steel is worked. Making it from raw iron ore is even more intensive. In fact, the production of steel and that other construction staple, concrete, accounts for as much as 16 per cent of humanity’s annual carbon dioxide emissions. That is equivalent to the carbon footprint of the US.

In the fight against climate change, heavy industries are the final frontier. Decarbonising transport and energy is the easy part. Steel and concrete are different beasts. It is much harder to produce them without releasing enormous amounts of CO2 into the atmosphere. And yet if we want to reach net-zero carbon targets, we can no longer ignore them.

Cleaning up concrete and steel is such an immense challenge that it can seem hopeless. But researchers and forward-thinking companies are pioneering clever ways to crack the problem – perhaps pointing the way to a crucial climate win.

The need to act couldn’t be clearer. If we don’t keep global temperature rises below 1.5°C, droughts, floods and extreme heat are predicted to be much worse. Natural treasures such as corals, not to mention all manner of other life forms, may be annihilated.

To avert disaster, we need to reduce carbon emissions to zero as soon as possible, and certainly no later than the middle of the century. In the parts of our economies that emit the most CO2, such as transport and energy, we have most of the technology we need to make that happen. Electricity generation can flip to low carbon sources such as wind and solar, cars can switch from combustion engines to battery power, and buildings can be insulated so that they use less energy. We just need to generate the will to implement these changes.

Solutions are nowhere near as obvious for heavy industry. The world produced more than 1.8 billion tonnes of steel last year, for example. Concrete production is even higher, and demand for both is likely to grow for decades. Both industries seem to fly under the radar in the climate conversation, but make no mistake, they produce whopping amounts of carbon. “They are responsible for half of all industrial emissions,” says Julian Allwood at the University of Cambridge, who was lead author on the problem of industry’s carbon footprint for the most recent major report by the Intergovernmental Panel on Climate Change. Although efficiency drives have reduced the footprint from steel and concrete to a degree, they still have a long way to go to clean up their act.

Reuse and recycle

The problem for both materials is that their production processes seem almost unavoidably carbon intensive, and tried and tested, scaleable alternative processes have been conspicuous by their absence.

Most steel is made using a combination of a blast furnace to extract iron from its ore and a basic oxygen furnace to convert this raw iron to steel. In essence, iron ore is heated by burning carbon-rich coking coal, creating CO2 as a by-product. Hence, “the major thing would be to shift away from blast furnace operations”, says Paul Fennell of Imperial College London.

One alternative is to recycle more. It is a simple enough process: put scrap steel into an electric arc furnace, where electrodes produce current that melts the steel so it can be reworked. This can reduce carbon emissions by about two-thirds for each tonne of steel produced compared with that made from iron ore. The electricity can, in principle, come from renewable resources.

That sounds like a win-win. Liberty Steel, the owner of the steel rolling mill I visited in Newport, certainly seems to think so, because it has plans to recycle a lot more steel. The mill isn’t far from Uskmouth B power station, a 1950s coal-fired power plant that has been dormant since 2017. Now, Liberty’s parent company GFG Alliance is spending £200 million on converting the power plant to a lower-carbon fuel: pellets made from non-recyclable plastic and other waste. It will send much of its electricity straight to the steelworks, where the firm hopes to build an electric arc furnace.

The wrinkle at this stage is that some sectors, such as car manufacturers, still prefer to use virgin steel. One concern is that impurities like copper can build up and make recycled steel poorer quality, reducing its potential uses. “At the moment, we can make construction grade steel from recycling, but not automotive grade,” says Allwood. Yet he adds that such impurities can be minimised by better sorting of materials before recycling them and by removing impurities from the molten steel.

The other option is to make fresh steel using a greener process – and to that end there is a push in some quarters to convert iron ore not with coking coal but hydrogen. The idea is that the oxygen in the iron ore will combine with the hydrogen to produce water instead of CO2. SSAB, a steel-making company headquartered in Stockholm, Sweden, is among those exploring this strategy, which it has called HYBRIT. It has begun construction of a pilot plant in Sweden that could, the firm claims, produce steel with “virtually no carbon footprint”.

“Many observers think concrete production is almost impossible to decarbonise”

There is a caveat. For the moment, hydrogen is overwhelmingly made from fossil fuels, such as natural gas, and that means greenhouse gas emissions: the carbon footprint of global hydrogen production is on a par with the emissions of the UK and Indonesia combined. But it is possible to make hydrogen from water using an electrolyser powered by electricity from renewable sources. If we one day have enough excess wind power, we could potentially produce all the hydrogen we need for large-scale clean steel production via electrolysis – that is, if the economics somehow worked out.

Promising. But part of the problem when it comes to decarbonising steel is the state of the industry. Unlike oil and gas, which continue to yield extravagant profits for producers, steel makers outside China are struggling to stay afloat. As a result, they don’t have much leeway to cover the costs of new low-carbon technology. Nor have they enjoyed the support of governments in the same way as the renewable electricity sector, which has benefited from subsidies for over a decade.

SSAB says its hydrogen-produced steel could be 30 per cent more expensive than normal steel, meaning it would require governments to introduce some form of carbon levy on steel production to make it economically competitive. “Until you think there is going to be a significant and sustained carbon price, the commercial driver is just to produce iron and steel in the way you already produce it,” says Fennell.

Concrete suffers with many of the same problems, starting with the basic chemistry involved in its production: CO2 emissions are inherent in making its component parts. Take cement, the “glue” that holds concrete together. To make it, you first grind and heat limestone in rotating kilns. The ensuing process of calcination decomposes the limestone’s calcium carbonate into calcium oxide, releasing CO2. The next stage requires yet more energy to heat calcium oxide with other materials to make a substance called clinker. Add this to the soft mineral gypsum and you get cement.

Many observers think the sector is almost impossible to clean up. Allwood puts it bluntly: “There are no options to decarbonise cement.” But that hasn’t stopped people from trying.

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Pouring concrete at a building development in Montreal, Canada

Aram Hovsepian/

One option is to use a different kind of cement. Almost all concrete is made using Portland cement, a 19th century formula that works well. But there are plausible alternatives. Some carbon savings are already made by using existing cement substitutes. One is fly ash, a fine powder produced as a by-product by coal power stations. Another is a by-product of iron-making called ground granulated blast-furnace slag. But we are trying to phase out coal plants for good reasons, and there is only so much of this slag .

Elsewhere, researchers have started looking at using a calcium silicate slag that is a by-product of the steel industry as a substitute for cement. It is typically dumped in landfills. Carbicrete of Canada is one firm eyeing this route and promises great carbon savings, but it is unclear, commercially speaking, if it has made any inroads.

All of these new formulations share two main problems. The first is a familiar one: they are more expensive than the current recipes. The second is a consequence of the first. No one is making them in volumes that would start to bring costs down. “There are alternative cements being developed in labs, but none at meaningful scale,” says Allwood.

A glimmer of hope can be found in Lixhe, Belgium, where researchers are experimenting with a different approach. Here, a plant owned by German company HeidelbergCement has been retrofitted with a 13-storey tower designed to capture the carbon produced during cement-making before it gets into the atmosphere. The aim of the Low Emissions Intensity Lime And Cement (LEILAC) project, partly funded by the European Commission, is to test a new technology – one that separates the CO2 released from other waste gases, to capture a pure stream of CO2.

Capture and convert

Fennell, who is involved in the project, believes it has promise in part because the CO2 could be a commodity to sell to other industries, such as plastic manufacturing. “It’s one of these rare processes that might have very little downside,” he says.

Scaling up could have an eye-watering price tag, though: LEILAC is a €21 million scheme, but will handle just 2 per cent of production at Lixhe, a typical-size cement plant. That hasn’t stopped HeidelbergCement pushing ahead with a report, based on a similar trial at a Norwegian cement plant, that will have a big say on whether it sinks funds into a full-scale project in Norway.

“The quickest climate win for concrete and steel might be the simplest: use less of it”

In principle, carbon capture and storage technology could help mitigate the carbon footprint of both concrete and steel. It is often mooted as a potential solution in the energy sector, and Luke Warren of the UK Carbon Capture and Storage Association says attention is beginning to turn to its use in heavy industry.

However, the truth is that the technology is still in its infancy. Despite its undoubted promise and years of efforts to make good on it, there are only 23 large-scale facilities in the world, capturing 40 million tonnes of CO2 a year, chiefly in natural gas processing plants where it is easier to implement. That amounts to just 0.1 per cent of humanity’s emissions.

Ultimately, the quickest climate win for both concrete and steel may end up being the simplest: use less of it, and make what we do use last longer. In the book Sustainable Materials: With both eyes open, Allwood and his colleagues sketch out how we could cut the emissions from these two materials by 50 per cent by 2050 by designing buildings to use less of them. A case in point is the velodrome built for the 2012 Olympic Games in London, for which the choice of a lightweight roof made of steel cables meant using 27 per cent less steel than a conventional arch-based design would have required.

Similar approaches are being explored for concrete. “Our mantra is use enough material and no more,” says architectural researcher Paul Shepherd at the University of Bath, UK. In January, he started construction of an office building using concrete beams that can bear the loads needed but are shaped to require less material than usual. And in some cases, we could just use wood instead.

Back at the steelworks in Newport, management are understandably hoping to ramp up the amount of metal they turn out. If things go to plan, output could double next year. And yet globally, the most credible and readily available route to a low-carbon future lies in the opposite direction. That is certainly how Kirsten Henson at KLH Sustainability, a construction consultancy that advised the London Olympics, thinks about steel and concrete: “We’ve got to use less of it,” she says.


Concrete and steel aren’t the only industries that need cleaning up if we want to reach net-zero carbon emissions


Aluminium production accounts for about 1 per cent of global carbon emissions. The problem comes when aluminium ore is converted to pure metal. This involves inserting an electrode made of carbon, which combines with oxygen in the ore to produce CO2. Last year Apple, a major aluminium user, announced a partnership with miner Rio Tinto and aluminium maker Alcoa to develop an alternative electrode that would produce oxygen instead of CO2 as a by-product. But the technology won’t be commercialised until 2024.


Making plastics is energy intensive, and the raw materials for producing them are often obtained from the refining of crude oil. That means they come with a sizeable carbon footprint. The good news is that increasing use of renewable energy, the rise of plastic recycling and reduction in demand could bring emissions to 2015 levels by 2050, according to a study published in April. Oil giant BP says bans around the world on single-use plastics – like those planned by the EU and Canada – will also curb growth in the demand for crude oil.


Ammonia, a key ingredient in fertilisers, is made from nitrogen and hydrogen. The latter is almost always made from fossil fuels, primarily natural gas – and the most common production process for turning it into ammonia, known as Haber-Bosch, is energy intensive. Emissions could be cut by making the hydrogen from natural gas but also using carbon capture and storage, or making it via electrolysis of water powered by renewable energy, but one analysis says such approaches add 60 per cent to the cost of ammonia production.

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