Concrete is the most abundant manufactured material on earth. It provides the literal foundations of modern life, but this comes with a high environmental cost.
We may think we are living in the age of plastic—indeed, in the last 60 years we have produced around 8bn tons of the stuff—but the cement industry alone makes more than this every two years. Perhaps because of its sheer ubiquity, concrete can have many meanings in many different contexts. It’s at once old and new, traditional and innovative, natural and artificial.
But what exactly is concrete? How has it been used and abused in the past? What is the effect of all this concrete on the planet? And is there anything we can do to lessen its impact?
What is concrete?
Concrete is a mixture of sand, stones, water and cement. It is a liquid that can be poured into almost any shape and in time turns into a rock-like material.
Cement is the key ingredient that makes concrete special. Ordinary Portland Cement is the most common form. It is made up of about three parts limestone to one part clay, which has been heated to around 1500°C and then ground down to a powder.
The ancient history of concrete
We may think of concrete as a modern material, but it has actually been used for thousands of years. Forms of concrete dating back to 6500 BCE have been found by archaeologists in Syria.
The Romans made use of pozzolana (a type of volcanic ash) to make concrete from about 300 BCE, with the roof of the Pantheon, finished in around 125 CE, still the largest unreinforced concrete dome in the world. The Romans used concrete right across Europe up until the fall of the Empire in the fifth century.
The beginnings of modern concrete
We don’t really know why, but concrete was not used again for over a thousand years. An early ‘modern’ use of concrete was in the 1750s, when British civil engineer John Smeaton was commissioned to construct a lighthouse off the coast of Cornwall.
Smeaton experimented with Roman pozzolana to make a new ‘hydraulic lime’ (which set underwater), finishing his Eddystone lighthouse in 1759.
Portland cement, patented by Joseph Aspdin in 1824, set the standard for the production of modern concrete. It was used in the foundations of the new Palace of Westminster in 1840 and from then until now, has been used in truly vast quantities for building and construction in all parts of the world.
Set concrete is extremely resistant to squashing—we say it has a high compressive strength. However, it doesn’t take too kindly to being bent—it has a relatively low tensile strength.
These properties of compressive strength and relative tensile weakness meant that 19th-century engineers favoured concrete for particular applications, such as for the foundations of buildings.
Reinforced concrete: Revolutionising building
The addition of iron or steel metal within concrete—so-called reinforced concrete—greatly increased its tensile strength and allowed new opportunities for its uses. When a Newcastle plasterer named William Wilkinson took out the first patent for combining concrete with iron bars in 1854, a new composite structure that would change the face of the planet was born.
Successive trials and tests followed over the decades, but it was only after French engineer Francois Hennebique patented his system of building with reinforced concrete in 1892 that the revolution began.
The first building in Britain to be built using reinforced concrete was Weaver’s Mill in Swansea, South Wales, completed in 1898. It used Hennebique’s system, which quickly became the most widely adopted method across Britain and Europe.
A symbol of modern life
The 20th century was truly the age of concrete. In the 10 years following Hennebique’s Weaver’s Mill, over 40,000 structures were built using his system alone. The concrete floodgates had been opened, and they’ve showed no signs of closing ever since. Docks, dams, roads, bridges, tunnels and flyovers all made use of this apparent wonder material.
We’ve had the Stone Age, the Bronze Age and the Iron Age. From the dawn of the twentieth century … is the Concrete Age.
J Winn, ‘The Advent of the Concrete Age' (1906)
But its uses weren’t limited to infrastructure projects and civil engineering; Britain’s whole built environment was turning grey.
After the Second World War, state-led projects to rebuild much of urban Britain employed concrete as the material of choice. For the creators of the new towns around Britain—from Crawley to Cumbernauld and from Runcorn to Redditch—reinforced concrete was used to rapidly construct new schools, hospitals and housing estates. These concrete buildings became the physical manifestations of the new politics of the Welfare State.
A determination to make things better saw highly expressive forms, such as the Barbican Estate in London, exemplifying architecture in the raw—also known as Brutalism. By the mid-1960s most British towns had at least one concrete multi-storey car park. The design of these modern concrete buildings was also often functional. The Welbeck Street car park, just off London’s Oxford Street, for example, used striking diamond-shaped precast concrete units, which provided a bold façade but also acted as load-bearing walls, thereby negating the need for internal columns.
New large-panel precast concrete systems were used to create office blocks and high-rise flats, changing the skylines of our towns and cities. Reality didn’t always reflect the utopian dream, however. The fragility of public confidence was made only too clear by famous failures, such as the collapse of Ronan Point flats in London in May 1968.
The environmental impact of concrete
Concrete is now the most widely used manufactured material on the planet. It has shaped so much of our built environment, but this comes at a massive environmental cost.
Cement is the key ingredient that makes concrete such a useful building material, and we use over 4 billion tonnes of it globally every year. Cement production alone generates around 2.5 billion tonnes of carbon dioxide (CO2) per year—about 8% of the global total.
Making cement requires the use of long rotating kilns the length of two football pitches, which are heated to around 1,500°C. The chemical process which turns the raw materials of limestone and clay into cement also releases high levels of CO2.
The environmental impact of concrete, however, goes further than the large amount of CO2 released into the atmosphere through cement production.
Such widespread use of concrete is also exhausting our diminishing supplies of useable sand (desert sand is too smooth and rounded for use in concrete). Moreover, concrete consumes almost 10% of the world’s industrial water supplies.
If we add to this the amount of steel used within reinforced concrete structures and the miles travelled transporting raw materials from the quarry to the cement mixer, the truly vast impact of concrete use on our planet is easier to understand. We simply cannot continue in this way.
Sustainable concrete: Can technology save us?
With these dire statistics in mind, what can we do? We can’t simply turn off the concrete taps at a stroke.
Part of the solution might come from an exciting process known as carbon capture and storage. Trees are already doing this, of course, but captured CO2 can also be injected directly into concrete mixes, locking it up permanently within the set product and even increasing the concrete’s compressive strength. Carbon-negative aggregate can also be used to reduce the overall carbon impact of concrete.
Another active area of research being undertaken by university departments and private businesses across the world is creating specialist concrete mixes, with wide and varied environmental benefits. Waste materials—such as ash from coal-fired power stations, ground-down blast furnace slag, micro silica, recycled plastic and even old concrete—are added to the mixture, reducing demand for natural resources and making use of otherwise useless materials.
Other, more specialist concretes include bio-cement, which contains micro-organisms that can heal cracks; concrete with microchips in the mix, which relay information on movement; self-cleaning concrete infused with titanium oxide; and graphene-enriched concrete, which is extremely strong and more water-resistant.
By adding different types of fibres, from basalt to glass to natural fibres, the performance and qualities of concrete can be significantly changed to suit specific needs.
Hempcrete, for example, uses chopped hemp to produce a lightweight, non-structural concrete, with good sound absorption and excellent heat and humidity-regulating properties. As a fast-growing plant, one ton of harvested hemp will have absorbed two tons of CO2, so this carbon gain is passed on to the building.
The future of concrete
All these efforts to improve the sustainability and performance of concrete might sound promising, but they are unlikely to solve all of its environmental problems.
The concrete industry is making big strides to clean up its act, and it’s certain that some of these innovations will form part of a more sustainable concrete future, but much more needs to be done to get these promising low-carbon products into widespread use.
The reality is that too much ordinary concrete, with all its damaging environmental impacts, is still being poured across the globe in vast quantities, and will continue to be well into the future. Every time you flush a toilet, you’re using concrete. When you walk on pavements, drive on roads, or fly in planes, you’re using concrete. Your hospital, school, office and possibly even your home is made, in part, from concrete.
Our modern world’s thirst for concrete seems unquenchable. We must fundamentally change our relationship with this revolutionary but complex and harmful material.
Though it dominates our modern built environment, we must find ways to massively reduce our concrete use if we are to effectively combat the legacy and future impact of the humble concrete mix.
Find out more
- Barnabas Calder, Raw Concrete: The Beauty of Brutalism, 2016
- Peter Collins, Concrete: The Vision of a New Architecture, 1959
- Norman Davey, A History of Building Materials, 1961
- Adrian Forty, Concrete & Culture: A Material History, 2012
- John Grindrod, Concretopia: A Journey Around the Rebuilding of Postwar Britain, 2014
- Frank Newby (ed.), Early Reinforced Concrete, 2001
- John Smeaton, A Narrative of the building and a description of the construction of the Edystone Lighthouse, 1791
- James Sutherland, Dawn Humm and Mike Chrimes (eds), Historic Concrete: Background to appraisal, 2001
- J Winn, ‘The Advent of the Concrete Age,’ Concrete and Constructural Engineering, Vol. 1, No. 1 (March, 1906)
- Science Museum Blog, John Smeaton's Whirling Speculum
- Nature, Seawater is the Secret to Long-lasting Roman Concrete
- ArchDaily, What is the Future of Concrete in Architecture?