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Concrete: do architects have their heads in the sand?


A report showing cement is responsible for 8 per cent of world CO2 emissions has sparked a debate over the profession’s love affair with concrete

Daddy Pig is very fond of concrete. The bumbling character in the wildly popular kids’ cartoon Peppa Pig, a probable architect and father of Peppa herself, even becomes the butt of a joke in one episode because of it.

Scouring around for a suitable bedtime story for herself and younger brother George, Peppa stumbles upon his library book The Wonderful World of Concrete and persuades Daddy Pig to read it aloud, a move that instantly sends everyone else in the family to sleep, including Mummy Pig.

It’s safe to say that most architects are firmly in Daddy Pig’s concrete-loving camp. So the news that the material plays not just some part, but a major part in our lurching progression towards a global warming catastrophe will be uncomfortable for many. 

Research by the think tank Chatham House, reported by the AJ earlier this month, found that production of concrete’s key ingredient, cement, is responsible for 8 per cent of global CO2 emissions (see below), and called for urgent decarbonisation strategies, but also pointed out the rapidly growing global demand for concrete.

It’s really difficult to produce a very good exposed concrete building and, for that reason, architects regard it as a virtuous material

A provocative tweet by this author drawing attention to the story and accusing architects of ‘fetishising’ the ‘planet-killing’ material then sparked a debate with members of the profession variously putting forward alternative approaches, defending concrete and even denying that man-made global warming exists.

So why has this news hit such a nerve and just how inseparable are architects and concrete? Furthermore, what alternatives are there to our current use of this material? And how likely is it that these can lead to a step-change in architect practice in the 12-year window the UN Intergovernmental Panel on Climate Change says we have to substantially reduce carbon emissions?

Concrete certainly has a special place in many an architect’s heart owing to its appearance, versatility, tactility and durability and its starring role in the Modernist and Brutalist movements.

Concrete shutterstock webcrop

Concrete shutterstock webcrop

Source: Shutterstock

For Adrian Forty, professor of architectural history at the Bartlett and author of Concrete and Culture, concrete is revered not only because of its historical links with Modernism but because it provides a challenge to designers when used as a visible part of a building.

‘It’s really difficult to produce a very good exposed concrete building and, for that reason, architects regard it as a virtuous material,’ he says. 

‘If you can do concrete well, you’re a good architect. You can show you can do something that equals a Modernist masterpiece.’

In addition to this compelling aesthetic challenge, there’s the opportunity concrete provides in terms of the structural feats it can accomplish, something demonstrated as far back as the dome of the Pantheon in Rome.

While acknowledging its high carbon footprint, writer and critic Owen Hatherley lauds it as a ‘wonder material’.

He says: ‘The interest in concrete is primarily because you can make it do things. So much engineering is reliant on it. It’s also extraordinary in terms of texture when you look at the National Theatre or the Walsall Art Gallery.’

Hatherley is sceptical that architects will stop specifying concrete without government intervention, particularly given the conservatism of the UK construction industry compared with more forward-thinking industries like that of Sweden.

‘There’s a minority of architects pushing alternatives and I welcome that,’ he says. ‘But by and large, architects do what the regulations tell them to do.’

If we have little more than a decade in which to restrict global warming, then embodied energy becomes the most pressing requirement

Until now, many have also argued that concrete is a sustainable material because of its relative longevity and high thermal mass. When assessed purely in ‘whole life’ terms, they have a point. 

But if you accept the scientific consensus that we have little more than a decade in which to keep global warming to a maximum of 1.5°C, then embodied energy becomes the most pressing requirement for a construction industry responsible for 35-40 per cent of all carbon emissions in the UK.

And there are signs that architects are waking up to this and the latest news on concrete.

Only last July the AJ featured concept designs for a new 300m² in-situ concrete home in rural Hampshire by Highgate-based Coppin Dockray.

But since the Chatham House research was publicised, this small practice has been considering a change of material.

‘This really affects how architects think about their projects,’ says co-founder Bev Dockray. ‘If this project goes ahead, I think we need to do some research about the materials and decide if we do use concrete. 

‘Most of our buildings are timber, but on this site there was an existing house made of concrete so there was support for the design echoing what was there.’

The hive c huftonandcrow 1

The hive c huftonandcrow 1

Source: Hufton + Crow

The Hive library in Worcester by Feilden Clegg Bradley Studios boasts a concrete frame made with 50 per cent GGBS

The RIBA is also beginning to highlight the importance of embodied carbon. It published a paper last year on the subject by carbon-profiling expert Simon Sturgis and joined a task force aiming to establish a working industry definition for zero net carbon buildings established by the UK Green Building Council.

So what exactly should architects, perhaps inspired to make a change like Dockray, be doing differently?

One of the answers is simply to prioritise refurbishment over new build where possible and to consider how buildings can be taken apart and reassembled and designed with this in mind.

Architect Duncan Baker Brown of BBM Sustainable Design is a strong advocate for the circular economy and reuse and recycling of local construction materials. He argues that a counterintuitive shift is needed away from ultra-low-energy-in-use systems such as Passivhaus to slightly more ‘leaky’ buildings that are reusable and cheap to produce in energy terms. 

Such arguments will surely only strengthen as the National Grid’s low-carbon credentials continue to improve thanks to the rapid growth of renewables capacity.

Another way forward is to use concrete and cement much more sparingly.

Structural engineer Chris Wise of Expedition Engineering argues that buildings are routinely designed with more concrete and steel than needed and suggests taxing such materials in the same way as petrol.

‘Lots of people are looking at what to do about carbon emissions, but clients ignore this as they’re just interested in the money,’ he says. 

‘Lean design principles mean not only are you using less material and less embodied energy, but it’s also potentially cheaper, although it does require more collaboration between team members and costs more in fees.’

An architect buys locally grown tomatoes, gets on their bike to work and thinks they are an environmentally conscious person while designing a concrete or steel-frame building

Wise says architects tend to be interested in this subject ‘to a degree’ but slams what he sees as examples of buildings where aesthetics have ‘trumped’ concern about embodied energy impact, such as Zaha Hadid’s 2012 London Aquatics Centre.

‘Because architects have a controlling hand in buildings, they are prone to misuse that power to produce things that are profligate,’ he says.

There is also growing interest in using recycled aggregates in concrete and replacing cement with low-carbon alternative ingredients such as GGBS (ground granulated blast furnace slag) and PFA (pulverised fuel ash), both ironically by-products of heavy industry.

Practices such as Feilden Clegg Bradley Studios and LTS Architects have experimented with such technology, with the latter regularly achieving a 40-50 per cent level of cement replacement in concrete used in its projects. While this is often cheaper, the downside is such concrete cures far more slowly than conventional concrete and there are not sufficient supplies of these cement alternatives.

So why aren’t architects starting to turn their backs on concrete? Certainly it remains vital for infrastructure projects in our rapidly urbanising world but – foundations apart – is it really necessary as a core part of the projects most architects work on day to day?

Practices such as SOM and Waugh Thistleton are strongly pushing timber and particularly cross-laminated timber (CLT) as a viable alternative, not least because trees absorb CO2 as they grow. In a recent opinion piece for the AJ, Anthony Thistleton argued that what is needed is a worldwide network of working and sustainable forests and that mass CLT building is the means to create it.

Waugh thistleton orsman rd

Waugh thistleton orsman rd

Source: Waugh Thistleton

Waugh Thistleton’s high-rise CLT project, 6 Orsman Road, London, currently on site

‘The simple truth is that we will only create more forests at the scale required if we massively increase demand,’ he wrote. ‘We also need a use for the harvested timber to ensure that the CO2 stored is permanently secured.’

Others such as Amin Taha point to the benefits of using stone in the way his practice did at 15 Clerkenwell Close.

‘We’re now advising all our clients to either go for stone or full CLT for walls and floors with a rainscreen cladding on the outside,’ Taha says. 

He is particularly evangelical about stone, saying it has only 10 per cent of the carbon footprint of a steel or concrete-frame building ‘even if you bring it in from abroad’ and is cheaper to boot.

‘The problem is lots of contractors are set in their ways,’ he adds.

Architects should not imagine that they are the virtuous ones, however. Speak to Taha’s engineering collaborator on Clerkenwell Close, Steve Webb of Webb Yates Engineers, and his anger about us sleepwalking towards disaster is quickly apparent.

‘It’s absolutely outrageous that an architect goes out and buys locally grown tomatoes at the supermarket, gets on their bike to work and thinks they are an environmentally conscious person while designing a concrete or steel-frame building,’ he says. 

‘Architects and engineers are the ones making decisions, so why don’t they engage with this?’

Comment: We need to talk about concrete

By Fran Williams, AJ technical editor

Cement works

Cement works

Source: WikiArt

Cement Works no 2, 1934, by Eric Ravilious

It’s the ingredients used in producing concrete that are the contributors to climate change, with cement the primary culprit. The industry emits nearly 900kg of CO2 for every 1,000kg of cement produced – primarily the result of its necessary, but heavy reliance on abundant raw materials.

Cement comes in several forms and is generally made up of Portland clinker, gypsum, supplementary cementitious materials, fillers and water. It is then bonded with a composite of fine and coarse aggregate, which hardens the material.

More than half the sector’s emissions are released by the calcination of limestone to produce clinker

Most of the emissions are intrinsically linked to the process for producing clinker. More than 50 per cent of the sector’s emissions are released by the calcination of limestone to produce this by-product, while a further 40 per cent is generated through the burning of fossil fuels to heat the kilns for the process – emissions that cannot be simply reduced by using alternative fuel sources or increasing the efficiency of cement plants.

And it’s not just clinker production that is a problem. The ‘binder’ used to bond with the fluid cement is made up of a high concentration of sand. The mining, dredging and even stealing of that sand has become a huge problem. No less than 30 billion tonnes of sand and gravel is extracted every year purposely for the building industry, and this is having an extreme environmental impact on ecosystems as beaches and river beds are stripped all over the world. 

Given that sand is the second-most used resource in the world after water, and can take thousands of years to form, this is an exponentially growing problem. Beaches are disappearing, farmland is becoming flooded with seawater and riverbeds are drying out – all as a result of such ‘sand mining’. 

And once sand is extracted from a river, for example, water flow can become more violent, lowering water levels in crucial bankside farming areas. In flood-prone zones where sand is essential in supporting the landscape as a sponge, this is increasing many communities’ vulnerability to storm damage.



Readers' comments (5)

  • The technology exists to make the cement manufacture process much cleaner in terms of CO2 production - it is called the Calcium Carbonate Looping process (CCL). This can isolate CO2 from exhaust gasses from the clinker production etc. and can even be organised that the waste product of the process is in fact the raw material of cement. It uses existing proven technology (fluidised bed systems) and is exothermic (i.e. it vastly reduces energy costs). Just needs the industry to invest, perhaps take slightly smaller profits, and do their bit to save the planet. There are a whole series of "carbonate looping" processes that have massive potential for future clean energy systems (e.g. thermite reactions). Effectively heat produced without exhaust gas...

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  • It's always a good idea to reduce CO2 emissions where possible, but making choices between materials needs a life-cycle analysis to be sure the reductions are real. We have used concrete structures on many occasions so that their thermal mass can help to stabilise internal temperatures and, in consequence, save energy in the long term. Various studies comparing timber or steel with concrete show a range of results, so it's not as simple as it sounds.

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  • It's probably about 20 years since I found - from, I think, Blue Circle's own information - that a tonne of cement produces a tonne of CO2. That makes it all the more important to preserve the embodied energy in buildings like Preston Bus Station (saved) or the Tricorn Centre (lost). A downturn in the cycle of popularity is really not enough. Think of the amount of concrete in the Aylesbury Estate.

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  • I agree completely with Rab Bennets above. You cannot make sweeping statements like this. The analysis should be comparative. i.e. concrete facade vs brick facade or aluminium facade, and concrete will have the lowest embodied energy by far (we have examples in our HBERT research). Even when compared to CLT, you still normally apply a rainscreen, and in some systems the sub-frame and rainscreen can add so much embodied carbon that it outweighs and saving from timber or stone. We need a lot more scientific rigor around this matter, the work from the UKGBC and LETI is a good start towards getting there but it will take a long time before the industry gets past this "concrete is evil" oversimplification. Steel is also around 8% of global CO2 emissions...

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  • To demand stop using concrete is almost as if asking someone to stop eating. There's currently no material able to replace concrete to building necessary infrastructure.
    In addition, any other material replacing concrete is likely to contain an even larger carbon footprint per tonne than concrete.
    Concrete's CO2 emissions per tonne sit near 100 kg.
    That of LVL, MDF, CLT and plywood sits at values larger than 350 kg/t according to the Univeristy of Bath's 'Inventory of Carbon & Energy' www.carbonsolutions.com/resources/ice%20v2.0%20-%20jan%202011.xls.
    Furthermore do the most common concrete's of today contain cement supplements such as fly ash and slag, reducing concrete's CO2 footprint substantially.
    Canada and the US have commenced using concretes commercially, where CO2 (captured from other industries) is injected and transformed into limestone. www.carboncure.com.
    I personally would not want to live in a timber building for health & safety reasons. Timber buildings could burn, rot and are hard to maintain. Sound absorption might be an issue.
    Only a concrete building provides that peace of mind I'm looking for in my home.

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