The Materials Book

261 Concrete is now universal. With six billion tons manufactured per year, it is the most used construction material in the world. But this glorious picture of urbanization may have obscured the complex and dual impact of concrete. While concrete continues to provide infrastructure and housing for billions of people, it has transformed our natural environment beyond the point of repair. Current cement production is associated with 8.6 percent of global anthropogenic CO 2 emissions. And in certain regions of the world, the scarcity of the natural materials used in concrete, including sand, aggregates, and water, has become alarming. Today, not only is urbanization not pairing with economic growth, but our current construction practices are threating human life. It is therefore urgent to rethink concrete and its production. More than 90 percent of the carbon dioxide produced by cement occurs during production. The process requires the calcination of limestone at 1,500°C; under such temperature, limestone, a calcium carbonate, chemically decomposes into calcium oxide to form ordinary cement and at the same time releases CO 2 gas. One kilogram of cement produces more than half a kilogram of carbon dioxide. The most common solutions are alternative materials to minimize ordinary cement content and an improved calcination process. Other technologies are under consideration; however, while academics and industry experts are increasingly focused on the environmental and economic value of new technology, less consideration is given to the actual use of concrete and the realities of the end user. Developing sustainable concrete Concrete as a Socio-technical Process Elise Berodier

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