Examining the global warming potential of hempcrete in the United States: A cradle-to-gate life cycle assessment

In the United States reducing greenhouse gas emissions associated with building construction by 90% by 2050 necessitates significant measures to be undertaken within the construction industry. Such measures include advanced construction techniques and bio-based material solutions such as hempcrete. This paper explores the mix design development and environmental impact assessment of hempcrete with an aim of reducing embodied impacts and achieving carbon negativity. Hempcrete being increasingly incorporated into both conventional and cutting-edge construction methods such as large-scale 3D printing is recognized as a carbon-negative material due to sequestered carbon in its constituent materials. Particularly, with the high carbon footprint associated with traditional Portland cement concrete, hempcrete presents a viable and low-carbon or even carbon-negative option for emerging construction techniques. The degree to which hempcrete achieves carbon negativity is contingent upon the proportion of hemp and lime within the mix design. Consequently, a comprehensive Life Cycle Assessment (LCA) is essential for evaluating the carbon-reduction potential of hempcrete. This study conducts a cradle-to-gate LCA of various hempcrete mix designs including a hybrid LCA of the environmental impact of domestically cultivated hemp. The results show that the global warming potential (GWP) of industrial hemp is −1.72 kgCO₂e/kg. The LCA of different mix designs reveals that carbon negativity is reached when the hempcrete composition includes no less than 20% hemp by weight. Moreover, findings underscore the importance of including lime's carbon absorption in calculations to attain carbon negativity as incorporation of hemp alone may not be adequate. The study concludes that optimizing the constituents of hempcrete to achieve carbon negativity is vital for effective climate mitigation and adaptation strategies.