Formulation of binder to improve mechanical properties of hemp concrete at early stage. Effect on thermal and hygric properties in use

Abstract

Hemp concrete is a bio-based material generally made of lime-based binder and hemp shiv currently used for building envelop. This lightweight material shows a thermal conductivity about 100 mW/(m.K). On hygric point of view, hemp concrete is strongly hygroscopic, with high moisture transfer and storage capacities. These properties allow hemp concrete to moderate ambient relative humidity variations. It is an excellent hygric regulator with moisture buffer values globally higher than 2 g/(m².%RH).On mechanical point of view, hemp concrete is a non-load bearing material. It gains mechanical resistance over the first few weeks after manufacturing. These mechanical performances depend, among other factors, on the properties of components and on the mix proportioning. In order to improve the mechanical resistance of hemp concrete at early stage, this study investigates new formulations starting from reference formulation. The binder composition varies by increasing the substitution rate of lime-based binder for selected calcium sulfate-based binder. This binder leads to interesting hardening at early stage. The effect on mechanical performances at long term appears effective, without large influences on thermal and hygric properties (maximal variation about 20% and 15%). Effective proportioning tool is then available.