Hempcrete from cradle to grave: the role of carbonatation in the material sustainability

The goal of reducing buildings impact to the environment is achieved by minimizing the energy consumption and through the employment of sustainable materials. However, the sustainability of building materials is assessed too many times considering a single phase of the material lifecycle (e.g. the use phase for good insulating materials). Even “LCA” studies focus sometimes on a single stage of the lifecycle, but this approach is particularly wrong for materials that improve or reduce their environmental performance during the operational phase or at the end of the building’s life. This is the case for materials containing lime, whose strength and sustainability increase theoretically along with the carbonatation process. An innovative building material containing lime is the hempcrete brick: a non-structural composite material obtained from a mixture of hemp shives (woody core of the hemp stalk) and a lime based binder; this material shows good thermal performances ( . m) and moisture buffering capacit. LCA studies about hempcrete materials either leave out the carbonatation process from the assessment or assume that lime is fully recarbonated in the use phase of the building. The goal of our study is to assess the real rate of carbonatation of hempcrete bricks in order to include the results in a thorough LCA study and to understand the weight this process can have in the overall sustainability of the material. The carbonatation rate has been evaluated on bricks produced by the Italian company Equilibrium Srl. The degree of carbonatation is evaluated through X-ray diffraction on samples extracted at regular intervals from the brick production up to 5 months. Carbonatation depth profiles are obtained too. Results show the importance of evaluating the behavior of a material in all the phases of the lifecycle and could be used for future LCA studies on hempcrete materials exposed to similar conditions.