One material has transformed the planet more than any other. Not plastic. Not steel. But concrete.
It is literally the foundation of the modern world - even when our homes aren’t built from it, they are usually built on it. From schools, hospitals and office blocks to bridges, dams and ports, concrete is everywhere.
The reasons are simple - it is versatile, long-lasting, cheap and easy to manufacture from abundant raw materials. It’s ingredients are just aggregate, water and cement, which is now the most widely used man-made material on the planet. First discovered in the ancient world, concrete was used by the Romans to build structures like the Pantheon and the Colosseum that are still standing today, 2000 years later.
The quantities of cement and concrete we now use are hard to comprehend. Every year we make more than 4 billion metric tons of cement, the majority of which is then used to make concrete. To put that in context, it’s estimated only 8 billion metric tons of plastic have been produced in the last 60 years.
And we are using more of it every year. Bill Gates wasn’t alone when he was astonished by this fact: China pours more cement every three years than the US did during the entire 20th century.
China is responsible for more than half of global cement production, and is home to the largest concrete structure ever made: the Three Gorges Dam, which used 16 million cubic metres of concrete. India is a long way behind, but as both its population and economy grow and are set to overtake China, it too is likely to consume vast quantities in the future, as will sub-Saharan Africa.
Concrete and cement are also the foundations for a huge slice of economic activity, creating jobs and forming the basis of the infrastructure improvements that drive growth and development. It’s even estimated that replacing all the world’s dirt floors with concrete would cut parasitic diseases by 80%, improving children’s health and even their cognitive abilities.
But the undoubted benefits of concrete and cement come with an increasing environmental cost. The production of cement is energy intensive (limestone needs to be heated to very high temperatures), and the chemical reaction itself produces carbon dioxide. It’s estimated cement is responsible for 8% of global carbon emissions. Another way of looking at it is that if the cement industry were a country, it would have the third-highest carbon emissions in the world, behind only China and the US.
There are other environmental costs too. Concrete is thirsty: it is responsible for 9% of global industrial water use, and by 2050 75% of concrete will be produced in regions which are suffering from water stress. Dust from construction sites and factories is a major factor contributing to air pollution in some countries. The demand for particular types of sand (used as aggregate) is driving the destruction of beaches, lakes and river beds. Land that has been paved over absorbs less water, so is more prone to flooding, and destroys the ecosystems that support greater biodiversity.
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Reducing the environmental damage done by concrete and cement will be crucial if the world is going to meet the goals set at in the Paris Climate Agreement, to cut emissions and limit global warming to less than 2°C. The cement and concrete industry will need to reduce its emissions by at least 16% by 2030. At the same time the industry is still expanding rapidly - production is on track to exceed 5 billion metric tons a year, and there are huge numbers of people living in slums who still need affordable housing and infrastructure.
It is a difficult task, but not impossible. A report by the Energy Transitions Commission makes it clear that achieving net-zero carbon emissions by the middle of the century is technically, and financially possible. But it will require a combination of ambitious policies by governments, accelerated innovation within the industry, and investment by all parties.
The scientific challenge is to develop forms of cement that are less energy intensive, and to use carbon capture technologies to reduce the actual emissions from the process itself. Most concrete today is made using something called Portland cement, which was developed in mid 19th century England. Research is underway into alternatives, with varying degrees of success: the key will be finding a balance between reducing emissions, and retaining the versatility and low cost that makes Portland cement such a popular material.
Recycling concrete and designing buildings and structures that use it more efficiently will also play a key part of any successful strategy, as will using renewable energy for kilns. But the technical challenges may seem easy compared to the political ones. As noted in the World Economic Forum’s report “Shaping the Future of Construction: A Breakthrough in Mindset and Technology”, the construction industry has been slower to adopt new technologies and adapt than other sectors. But the potential is there for even small changes to make a dramatic difference. And the rewards would be materials which can shape our world, without costing the earth.