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Material Nature versus Structural Nurture: The Embodied Carbon of Fundamental Structural Elements

Purnell, P.
Environmental Science & Technology 2012 v.46 no.1 pp. 454-461
carbon, carbon dioxide, construction industry, greenhouse gas emissions
The construction industry is under considerable legislative pressure to reduce its CO₂ emissions. The current focus is on operational CO₂ emissions, but as these are compulsorily reduced, the embodied CO₂ of structural components, overwhelmingly attributable to the material from which they are manufactured, will become of greater interest. Choice of structural materials for minimal embodied CO₂ is currently based either on subjective narrative arguments, or values of embodied CO₂ per unit volume or mass. Here we show that such arguments are invalid. We found that structural design parameters (dimensions, section choice, and load capacity) for fundamental structural components (simple beams and columns) are at least as important as material choice with regard to their effect on embodied CO₂ per unit load capacity per unit dimension, which can vary over several decades within and between material choices. This result demonstrates that relying on apparently objective analyses based on embodied CO₂ per unit volume or mass will not lead to minimum carbon solutions; a formal definition of the correct functional unit for embodied CO₂ must be used. In short, there is no such thing as a green structural material.