Industrial hemp, like any plant, removes CO2 from the air to undergo photosynthesis. It retains the carbon from the molecule and releases the separated oxygen back into the air. Plants use the extracted carbon to produce sugar molecules and then store the excess sugar in their stems and roots. Ordinarily, plants die and release stored carbon back into the atmosphere when they decay. However, when incorporated into a long-lasting building material, the carbon of the plant is trapped for longer than the plant’s natural lifespan admits. This means that the net removal of CO2 is higher for plant-based, long-lasting materials like Hempcrete.
Hydrated lime in the binder for hempcrete also plays a role in the trapping of carbon. In the process of refining the raw limestone, carbon is driven off with heat. This process gives the limestone powder a hydraulic set; it hardens when combined with water and begins the process of returning to limestone. The lime binder is mixed as a slurry and is used to coat the hemp hurd’s, which also absorb the binder. Once it begins to set, the lime embarks on its journey to re-capture the carbon driven off in the refinement process. Hydrated lime will literally vitrify and become limestone again over time.