Concrete is the most widely used material in the world: You see it in the streets you move through, and it might line your home or apartment. Globally, around 27 billion metric tons of concrete are produced each year.
But making cement–the mineral compound that constitutes the most crucial ingredient of concrete–is an extremely carbon-intensive process. It’s produced in factories with massive kilns where raw materials, like limestone, clay, and shale, are heated to temperatures up to 1550 degrees Celsius, then ground into a powder. Heating the cement minerals to such high temperatures poses a sustainability concern, says Kemal Celik, professor of civil engineering at New York University Abu Dhabi and the director of the Advanced Materials and Building Efficiency Research (AMBER) Laboratory. Producing cement accounts for around 7% of global CO2 emissions.
This fact, Celik says, got him interested in finding a better way to make the material. He and his team already knew that magnesium oxide, a mineral found in salt deposits like lakes and salt flats, could be converted into a type of cement. In the United Arab Emirates, where Celik and his team work, they realized they could tap the over 70 operating desalination plants for access to brine left over from the process of purifying seawater, which would otherwise just be dumped back into the Gulf. Synthesizing the magnesium oxide in brine into a cement-like substance requires much less heat than making ordinary cement. And, Celik says, as magnesium oxide cement hardens over its lifetime, it absorbs carbon dioxide over time to gain strength, potentially making it a carbon-negative building material.
Celik and his team at AMBER have already conducted tests showing that it’s just as strong and adaptable as ordinary concrete. And, Celik says, this method of making cement from leftover brine provides a crucial outlet for the desalination industry, which is quickly expanding in places that struggle with access to potable water, but struggling to dispose of its briny waste in a way that doesn’t alter the salinity levels in nearby bodies of water, which can hurt the surrounding ecosystems. Ultimately, the briny cement Celik and his team are advancing could be a way for the building industry to lower its associated emissions, both by reducing the amount of carbon needed to produce the material, and by the material over time pulling excess carbon from the atmosphere.