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Recycling Portland cement — emissions-free

| By Gerald Ondrey

The production of clinker used for making cement continues to be a major source of global CO2 emissions. Now, three engineers from the University of Cambridge (U.K.; have filed a patent and been awarded new research funding for their invention of what is said to be the world’s first emissions-free route to recycle Portland cement.

The inspiration for the so-called Cambridge Electric Cement struck inventor Cyrille Dunant when he noticed that the chemistry of used cement is virtually identical to that of the lime-flux that is already being used in conventional steel-recycling processes that use electric-arc furnaces (EAF). The new cement is therefore made in a virtuous recycling loop, which not only eliminates the emissions of cement production, but also saves raw materials, and even reduces the emissions required in making lime-flux.

The new process begins with concrete waste from the demolition of old buildings. This is crushed, to separate the stones and sand that form concrete from the mixture of cement powder and water that bind them together. The old cement powder is then used instead of lime-flux in steel recycling. As the steel melts, the flux forms a slag that floats on the liquid steel, to protect it from oxygen in the air. After the recycled steel is tapped off, the liquid slag is cooled rapidly in air, and ground up into a powder that is virtually identical to the clinker which is the basis of new Portland cement.

In pilot-scale trials of the new process, the Cambridge team have demonstrated this combined recycling process, and the results show that it has the chemical composition of a clinker made with today’s process.

The new cement was invented as part of the large multi-university UK FIRES program, led by professor Julian Allwood, which aims to enable a rapid transition to zero emissions based on using today’s technologies differently, rather than waiting for the new energy technologies of hydrogen and carbon storage. Invention of the cement has been rewarded with a new research grant of£1.7 million ($2.1 million) from the Engineering and Physical Sciences Research Council (EPSRC; Swindon, U.K.) for further development.