The road to low-carbon concrete

Enlarge / Cement Works, Ipswich, Suffolk, UK. (Photo by BuildPix/Construction Photography/Avalon/Getty Images)

Nobody knows who did it first, or when. But in the 2nd or 3rd century BCE, Roman engineers regularly ground burnt limestone and volcanic ash to make cement: a powder that would begin to harden as soon as it was mixed with water.

They widely used the still wet slurry as mortar for their bricks and stones. But they had also learned the value of stirring pumice, pebbles or shards of pot with the water: if you respect the right proportions, the cement would end up binding everything together into a solid, durable conglomerate resembling of the rock called caementicium opus or – in a later term derived from a Latin verb meaning “to gather” –concretum.

The Romans used this marvel throughout their empire – in viaducts, breakwaters, coliseums and even temples like the Pantheon, which still stands in the center of Rome and still has the largest unreinforced concrete dome in the world. .

Two millennia later, we’re doing much the same thing, pouring concrete by the gigatons for roads, bridges, skyscrapers, and all the other big chunks of modern civilization. In fact, globally, humanity currently uses approximately 30 billion metric tons of concrete per year, more than any other material except water. And as rapidly developing countries such as China and India have continued their construction boom for decades, that number is only growing.

Unfortunately, our long love affair with concrete has also made our climate problem worse. The variety of cement which is most commonly used to bind concrete today, a 19th century innovation known as Portland cement, is made in energy-intensive kilns that generate more than half a ton of carbon dioxide for each ton of product. Multiply that by the gigatonnes of global utilization rates, and cement manufacturing turns out to contribute about 8% of total CO.2 emissions.

Admittedly, this is far from the fractions allocated to transport or energy production, which are both well above 20%. But as the urgency to tackle climate change heightens public scrutiny of cement emissions, as well as potential government regulatory pressures in the United States and Europe, it has become too important to ignore. “It is now recognized that we need to reduce net global emissions to zero by 2050,” says Robbie Andrew, senior researcher at the CICERO Center for International Climate Research in Oslo, Norway. “And the concrete industry doesn’t want to be the bad guy, so they’re looking for solutions.”

Major industry groups like the London-based Global Cement and Concrete Association and the Illinois-based Portland Cement Association have now released detailed roadmaps to reduce that 8% to zero by 2050. Many of their strategies rely on emerging technologies; it’s even more about developing alternative materials and underutilized practices that have been around for decades. And everything is explained by the three chemical reactions that characterize the life cycle of concrete: calcination, hydration and carbonation.

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