After water, concrete is the most-used material on earth. In any single year, enough is produced to cover every single surface in the whole of England. A simple mixture of aggregates and a lime-based binding paste, its low price tag and accessibility have enabled cities across the world to create a thriving infrastructure that provides people from all classes with safe and sanitary shelter.
Concrete protects us from the elements, resisting both fire and water, its chief quality being to harden and then degrade exceptionally slowly. Constructed 2,000 years hence, Rome’s Colosseum and Pantheon are still worthy ambassadors for the material’s profound durability.
Naturally, because it can be poured into any form, concrete lends itself to all kinds of variety, from pioneering towers to utilitarian structures like car parks, dams and bridges.
Tim Bowder-Ridger, the principal of the London-based firm Conran and Partners, believes there is a charm to the sometimes minimalism of constructions such as the Centre Point Tower, which his team worked to revive in 2011.
“Simple forms can be expressed as the personality of the building,” he says. “The ability to create continuous shapes makes areas such as fire, sound and water-proofing more straightforward, saving on cost and materials.”
Certainly, the ease afforded by concrete – to be made on-site; to transport; to make its aggregate from whatever materials can be found locally; not to mention its low cost in comparison to other materials – makes it very appealing to designers.
Portland cement, the modern industrialised form of concrete’s binder, was patented in 1824 by Joseph Aspdin, and this was later the basis for art deco skyscrapers like New York’s Empire State Building, which was built in 1931.
After the Second World War, concrete was poured in abundance to rebuild cities ravaged by bombs, a time when Brutalist architects, such as Le Corbusier and Oscar Niemeyer, dreamed up radical free-flowing structures epitomised by the exotic sculptural forms of Niemeyer’s iconic master plan for Brasília and the plant-strewn confines of the Barbican Centre.
In Britain, debate on its aesthetics has historically been polarising.
For some, these buildings evoke images of urban squalor and drab, repressive Soviet blocks. For others, they are historical relics that need to be protected from the bulldozer. The most vociferous critics clamouring for their demolition include Prince Charles, who once described Owen Luder’s Tricorn Centre in Portsmouth as a “mildewed lump of elephant droppings”.
Bowder-Ridger would tend to disagree with HRH’s opinion of the material. “Concrete offers opportunities of theatre and sensuality,” he says. “It allows bold exploration of form through contrasts of light and shadow, texture, as well as inexhaustible choices of colour and tone.”
Concrete offers opportunities of theatre and sensuality. Tim Bowder-Ridger, principal of Conran and Partners
William Hall, the designer and author of the Phaidon titles Concrete, Brick, Wood and Stone, cites the Barbican as an example of the material’s artistic potential.
“You can see all different kinds of finishes there, including bush-hammering, which is where they put big pebbles in and get a mechanical hammer to bash away at it to reveal the pebble texture,” he explains.
“The Barbican has an unpretentious rigour to it. If you think of its three tower blocks composed in brick, it wouldn’t have the elegance that it has.”
Indeed, when you consider other finishes enabled by concrete, such as Caruso St John’s Nottingham Contemporary, which is imprinted with an intricate lace pattern, the creative possibilities of working with this liquid form appear endless.
But, like most things worth discussing, concrete comes with a caveat – the environmental impact of its production – as a colossal 2.8 billion tonnes of carbon dioxide is emitted across the globe each year. In more relatable terms, a concrete cube the size of a standard washing machine will have emitted the same amount of carbon dioxide as a car journey from London to Edinburgh and back again.
Many engineers argue that there is no viable alternative to concrete without compromising on cost – steel, asphalt and plasterboard are all more energy-intensive than concrete. Naturally, then, the industry needs to rethink the way concrete is made, and how much of it.
To reduce emissions, Bowder-Ridger believes the material needs to be used more sparingly and intelligently, “with an assumption that it should be considered as non-disposable”.
Dr Natasha Watson, the senior structural engineer at Buro Happold, agrees. “I believe that our current use of concrete is lazy. We need to treat concrete like a precious resource, using it only where necessary,” she says. “Carbon emissions are the primary cause of climate change as we know it today, and if we are to reach our targets to reduce global emissions by at least 55% by 2030 from 1990 levels, in accordance with the Paris Agreement, we need to really look at our use of concrete in the built environment.”
We need to treat concrete like a precious resource, using it only where necessary. Dr Natasha Watson, senior structural engineer at Buro Happold
Cement accounts for around 10% of the concrete mix, but alone is responsible for around 8% of global carbon emissions.
Seeking sustainable solutions
Watson calls for the replacing of ordinary Portland cement with other cementitious materials that have a lower embodied level of carbon, such as the waste products ground granulated blast furnace slag (GGBS) and pulverised fuel ash (PFA).
“Unfortunately, GGBS and PFA are waste products from the smelting of iron ore into molten iron, and the ash results from the burning of pulverised coal in coal-fired electricity generation,” she says. “But in the next five to ten years, GGBS and PFA will be appropriate cement replacements.”
However, as we move towards increasing steel reuse and less iron mining, as well as a reduction in burning coal for energy, there needs to be a more sustainable alternative.
The Dutch microbiologist Hendrik Jonkers thinks he might have found a solution, having developed a formula to prolong the lifespan of concrete further. His invention sees self-activating limestone-producing bacteria embed itself into concrete, to heal cracks that appear on its surface – the aim of which is to decrease the amount of new concrete produced and lower repair costs for cities and private homeowners alike.
“We know that concrete cracks, so therefore we have steel reinforcement embedded in it,” says Jonkers. “This can corrode when damp gets in, so our motivation was to find a solution to this problem.” His healing agent (a combination of bacterial spores and nutrients – ‘food for the bacteria’) needs water to activate, when it can then begin to make a certain product.
Therefore, Jonkers and his team mix the healing agent through the concrete so that only at the moment when concrete cracks and water gets in does the bacteria activate and start producing limestone to fill the cracks – making the structure watertight once again.
“Self-healing concrete reduces the need for steel reinforcement because steel is there for structural performance,” he says. “But part of the steel is there to ensure that when cracks occur, they only extend to a certain width. Self-healing concrete means you can allow larger cracks to occur because the bacteria will heal the crack.”
In a typical watertight construction, you apply 50kg to 60kg of steel, according to Jonkers. If you combine this with the self-healing agent, he estimates that you can reduce the amount of steel needed to 30kg or 40kg, making the building process less costly and reducing carbon footprint.
Reshaping solid foundations
It’s important to note that the environmental benefits to Jonkers’ formula could take decades to be seen, and many believe this to be time we do not have when it comes to reversing the effects of climate change.
“There’s no easy solution,” says Hall, “but the best thing is to stop destroying buildings.” Watson concurs, adding that we should prioritise looking at the buildings we already have in a different light and adapt them over time for what we need, “rather than throwing them away like fast-fashion and building new ones”.
Constructions like Bowder-Ridger’s Centre Point Tower, which achieved BREAM Excellence, is a fine example of how to approach our existing concrete behemoths. For its renovation, the firm reused almost all of the existing concrete of the original 1960s office building to create a residential building for 21st century needs.
Bowder-Ridger is all too aware of the environmental consequences of not preserving concrete buildings, which he has witnessed first-hand having worked on projects across East Asia, where many tonnes of concrete are demolished every generation, only to be replaced with new concrete frames. But, in earthquake areas such as Japan, there is currently no material better suited to withstand such pressures.
Perhaps emerging technologies will allow us to treat aged concrete buildings across the globe more like historic constructions, which are repaired, sustained and repurposed over hundreds of years. Certainly, in Europe, the tradition to rework and layer existing buildings with other materials creates a richness to our ever-changing built environment – and this, as Bowder-Ridger observes, transforms a worsening problem into a concrete opportunity.