Lime and hemp concrete LCA: a dynamic approach of GHG emissions and capture

Abstract

Lime and hemp concretes are well known and studied as low-impact materials for building. During the last two decades, a few studies have shown their interest in terms of environmental impacts such as embodied energy, air pollution or GHG emissions. On the other hand, new carbon footprint calculation methods were proposed to assess the value of temporarily storing carbon in long-lived products such as building structures and insulation. This is an important aspect for bio-based materials, as they capture and store carbon. From an environmental point of view, it would be of interest that GHG emissions due to cultivation, manufacturing, transportation, construction, demolition and end-of-life could be compensated by the beneficial effect of a long-term carbon storage. The principal aim of this study is to evaluate the long-term effect on climate change of using LHC in building. GHG emissions and uptakes were assessed using a dynamic life cycle assessment approach for several scenarios: 1) different cultivation practices for hemp (in the French context, surveys of 2014-2015 provided by the Cetiom), and 2) different mixes and formulations for the LHC, i.e. two classical ones: sprayed and cast LHC, and a more innovative one: compacted LHC. Whatever the formulation, a woody structural frame is necessary, composed of local timber wood (less than 100km from construction site). To take into account the emission dynamics, plants growing (trees and hemp) and carbonation of lime into the walls were considered. Optimum scenarios were compared, by taking the minimum and maximum impact for each mixes (different cultivation practices, transportation of lime and hemp, end-of-life scenarios). As a result, some LHC with high hemp/lime ratio, low-impact crop practices, and a proper end-of-life scenario could be a solution to stock carbon and keep a positive effect on climate, even on the long-term (more than 100 years).