How Much Carbon Can Construction Materials Store?

It has been well established that the built environment is a significant contributor of greenhouse gas emissions as a result of the production of construction materials and the energy consumed during operation. Yet, some construction materials, such as timber products and fast-growing grasses, have the ability to store carbon. A new paradigm has begun to emerge that evaluates buildings not only for their life cycle cabon emissions, but also for their potential to store and sequester carbon when these materials are used. The transition post-carbon cities will require the use of carbon storing materials because of their reduced life cycle carbon emissions. The present work provides a review of carbon storing materials with a focus on quantifying their ability to store or sequester carbon for inclusion in life cycle assessment. Focus is paid to two classes of construction materials: cementitious materials, and materials derived from biogenic carbon. Cementitious materials include concretes and mortars which store carbon through a chemical carbonation reaction. Biogenic materials are further classified based upon their harvest cycle length. Fast-growing materials (e.g., straw and hemp) are those that have a harvest cycle of less than 1 year, while slow growth materials (e.g., timber) have harvest cycles longer than 1 year. The storage potential of each material is considered from the perspectives of traditional, static life cycle assessment in addition to dynamic life cycle assessment. This review of carbon storing construction materials will provide building designers the tools necessary to quantify the carbon storage potential of buildings. By understanding not only the emissions of construction materials, but also their potential to store carbon, the paradigm of buildings as a carbon sink can be further developed and adopted by the architects, engineers, and urban planners.

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