It remains to be seen whether innovations like these can really get the concrete industry to a place where it emits no net carbon dioxide. Yet industry observers and insiders alike find plenty of room for optimism, if only because the momentum for change has built so rapidly. Remember, says Andrew, that as recently as a decade ago there seemed to be no feasible, climate-friendly alternatives to Portland cement at all. The stuff was cheap, familiar, and had a huge infrastructure already in place—hundreds of quarries, thousands of kilns, whole fleets of trucks fanning out to deliver pre-mixed concrete slurry to building sites. “So for a long time, decarbonizing cement production was in the ‘too hard’ basket,” he says.

Yet today, says Bohan, “because of this intense attention to the climate issue, people are now going back and saying, ‘Wow, we didn’t realize all these options were available.’”