Becca Tapert on Unsplash
Wet concrete has been poured into buildings, roads, bridges and more for centuries. Structures using concrete have survived wars and natural disasters, outlasting many of the civilizations that built them. Alongside its strength and resilience, concrete is also a staple of building because it is relatively cheap and simple to make. Worldwide, 30 billion tonnes of concrete is used each year. On a per capita basis, that is 3 times as much as 40 years ago — and the demand for concrete is growing more steeply than that for steel or wood.
Versatile and long-lasting, concrete buildings and structures are in many ways ideal for climate-resilient construction. But concrete has a colossal carbon footprint — at least 8% of global emissions caused by humans come from the cement industry alone. We must decarbonize its production.
Concrete is made by adding sand and gravel to cement, whisking the mixture with water and pouring it into moulds before it dries. Making the cement is the most carbon-intensive part: it involves using fossil fuels to heat a mixture of limestone and clay to more than 1,400 °C in a kiln. Also, when limestone (calcium carbonate) is heated with clays, roughly 600 kilograms of carbon dioxide is released for every tonne of cement produced.