The road to low-carbon concrete

Nobody knows when it happened or who did it. By the 2nd or 3rd century BCE, Roman engineers were grinding up burnt limestone and volcanic ash to make caementum, a powder that would start to solidify as soon as it was wet.

They used the still-wet slurry to make their brick and stoneworks. They had learned that it was important to get the proportions right and the cement to bind it all together into a rock-like conglomerate called opus caementicium.

The largest unreinforced concrete dome in the world still stands in central Rome and is one of the wonders of the Romans' empire.

We poured concrete for roads, bridges, high-rises, and all the other big chunks of modern civilization after two millennia. The human race uses an estimated 30 billion metric tons of concrete each year, more than any other material. As fast-developing nations such as China and India continue their construction boom, that number is only going to increase.

Our love affair with concrete has made our climate problem worse. The variety of caementum that is used to bind today's concrete, 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 every ton of product. Cement-making contributes about 8% of the total CO 2 emissions.

The fractions attributed to transportation and energy production are over 20%. As public scrutiny of cement's emissions increases due to climate change, it's become too big to ignore. A senior researcher at the CICERO Center for International Climate Research says that we need to cut global emissions to zero by the year 2050. The concrete industry doesn't want to be the bad guy.

Major industry groups like the London-based Global Cement and Concrete Association and the Illinois-based Portland Cement Association have now released detailed road maps for reducing that 8 percent to zero by datememe datememe. Many of their strategies rely on emerging technologies, as well as scaling up alternative materials and underutilized practices that have been around for decades. There are three chemical reactions that make up the life cycle of concrete.