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 the 8 percent that cement-making is contributing to the total of CO2 emissions, to zero by 2050.

Many of their strategies rely on emerging technologies; even more are a matter of scaling up alternative materials and underutilized practices that have been around for decades. And all can be understood in terms of the three chemical reactions that characterize concrete’s life cycle: calcination, hydration, and carbonation.