The Marin County, California Low Carbon Concrete Code was the first in the nation to address the negative environmental externalities of concrete when it added a mandatory low carbon concrete specification to the Marin County Building Code. That new code modified the 2019 California Building Standards Code regulating allowable mix design and materials for plain and reinforced concrete. The purpose of this code is to provide standards and requirements for the composition of concrete, that ideally maintains adequate strength and durability for the intended application and at the same time reduces greenhouse gas emissions associated with concrete composition. The code provides for substituting one of several pozzolans, such as fly ash, slag and other Portland cement replacements. Possibly most significant, the code provides a form of non-residential specification and residential specification that could be a model for construction contract provisions.
Embodied (or embedded) emissions are emissions of carbon dioxide and other greenhouse gases generated by making and transporting materials to a building site, including mining, refining, and shipping. Many green building programs actually encourage the use of concrete. Replacing cement with currently available alternative cementitious materials, such as fly ash or slag, and other practices to “decarbonize” concrete has the potential of reducing total emissions from concrete by more than half.