Concrete and steel production are major sources of CO2 emissions, but a new solution from Cambridge could recycle both at the same time. If done using renewable energy, the process could make for completely carbon-zero cement.
Concrete is the world’s most used building material, and making it is a very dirty business - which is why concrete production is responsible for about 8 percent of total global CO2 emissions. Unfortunately it’s not easy to recycle back into a form that can be used to make new concrete structures.
Scientists around the world are searching for ways to make concrete and steel in more environmentally friendly ways, and now it looks like the Cambridge team have discovered two solutions at the same time. “I had a vague idea from previous work that if it were possible to crush old concrete, taking out the sand and stones, heating the cement would remove the water, and then it would form clinker again,” said Dr. Cyrille Dunant, first author of the study. “A bath of liquid metal would help this chemical reaction along, and an electric arc furnace, used to recycle steel, felt like a strong possibility. We had to try.”
And sure enough, not only was it able to purify the steel just fine, but if the leftover slag is cooled quickly in air, it becomes new Portland cement. The resulting concrete has similar performance to the original stuff.
Importantly, the team says this technique doesn’t add major costs to either concrete or steel production, and significantly reduces CO2 emissions compared to the usual methods of making both. If the electric arc furnace was powered by renewable sources, it could essentially make for zero-emission cement.
"Producing zero emissions cement is an absolute miracle," said Professor Julian Allwood, who led the research.