Summary

1. Current methodologies do not account for the full natural carbonation that would occur in both the “business as usual” scenario and the reduced-cement project scenario.
2. Projects should account for the full carbonation process. This means considering a longer time horizon since natural carbonation can take decades to occur.

In reduced cement projects, natural carbonation occurs in both the baseline and project scenario. Minerals in the cement chemically combine with ambient CO2 in the atmosphere, creating a permanent bond (in the absence of extreme high temperatures). Under some methodologies, projects do not include natural carbonation in either the baseline or the project scenario, perhaps arguing “if it happens in both, it will cancel out and we don’t need to count it.’’ But the same amount of natural carbonation does not occur in both. The whole point of these projects is to reduce cement use and the associated emissions. However, less cement means less potential for naturally absorbing CO2.