If cement was a country, it would be the third biggest source of emissions after China and the USA, accounting for almost 8% of man-made CO₂ 
After water, cement is the most widely used substance on Earth. And when these two most widely used substances are mixed, they transform into the planet’s most widely used building material – concrete. The backbone of the construction industry, it forms our apartment blocks, schools, roads, municipal buildings, hospitals, offices, hotels, dams, bridges – all the underpinnings of how we live our lives. It effectively shapes the basis of the modern economy. But the cement industry is responsible for about 8% of planet-warming carbon dioxide emissions — far more than emissions from aviation for example (2.5%) and not far behind the global agriculture business (12%). 
As the key material for the vast majority of buildings, concrete has, for many, enabled the construction of some of the world's worst architectural eyesores. The concrete jungle summons up a vision of a bleak urban environment, dismal tower blocks evoking the worst aspects of municipal living, lending itself to the image of a dystopian film set world, austere and forbidding, with no greenery to soften the edges or provide any respite from the harsh city heat. 
Interior of the Pantheon, Rome, built by Agrippa between 25-27 BC, dedicated to the twelve Gods and to the living Sovran. Traditionally it is believed that the present building is the result of the radical reconstruction by Hadrian between 118 and 125 AD. 
But concrete is also the reason some of the world's most impressive and beautiful buildings exist. The Sydney Opera House, St Paul’s Cathedral in London, the Lotus Temple in Delhi, the exquisite Pantheon in Rome (one of my favourite buildings) - boasting the largest unsupported concrete dome in the world - all owe their form to the material. The earliest recordings of concrete structures date back to 6500 BC by the Nabataea traders in regions of Syria and Jordan. They created concrete floors, housing structures, and underground cisterns. Subsequent cultures all used concrete, but the Romans were the first to utilise it extensively, and by 200 BC were successfully using concrete in the majority of their construction. 
Concrete is made from sand, gravel and water with cement forming a binder. Only a small proportion by volume, but cement is responsible for almost 90% of concrete’s carbon emissions. In the process to make cement – known as clinkering – limestone and the other raw materials are crushed and then heated in large kilns to temperatures up to 1600°C. The heat is used to drive carbon dioxide from the limestone, leaving a residue of cement. 
Recycling cement would decrease its carbon footprint significantly. And switching to electric-powered furnaces, and using renewable energy from wind and solar rather than fossil fuels could mean no greenhouse gases from that part of the process would be released at all. A scalable, cost-effective method to reduce the emissions from concrete production while meeting global demand – which is not going to go away – is one of the biggest decarbonisation challenges, and will play a significant part in achieving net zero. 
This week, a major step forward in finding a solution has been announced by researchers at the University of Cambridge. Reported in the journal Nature, they have developed a method to produce very low emission concrete at scale. The research team say it is “an absolute miracle” – it uses the electrically-powered arc furnaces designed for steel recycling to simultaneously recycle cement, the carbon hungry constituent of concrete. 
The hope is this Cambridge Electric Cement will be cheaper to manufacture because it uses what is essentially waste heat from the steel recycling process. If it can be made to work profitably at scale, it could lead to huge reductions in emissions. The researchers estimate that, given current rates of steel recycling, their low carbon cement could produce as much as a quarter of the UK’s demand. 
And the use of electric arc furnaces is expected to increase in the future, potentially allowing more “electric cement” to be produced. Looking forward, the process could be duplicated all over the world, potentially cutting the emissions from cement dramatically. For a multibillion dollar industry responsible for a tenth of the world’s carbon emissions, it’s an exciting prospect. 
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