Thermal and mechanical properties of hempcrete with low-carbon binders: Effects of 3D distribution and orientation of hemp shivs and microstructures of hempcrete

Hempcrete is a bio-based composite having excellent thermal insulation properties. However, the influence of low-carbon binders on the microstructural and thermal behaviour of hempcrete has not been thoroughly investigated. This study presented the effect of the mechanical and thermal properties of hempcrete using three different binders, including hydrated lime, limestone calcined clay, and alkali-activated binder. To further analyse their microstructure and gain an in-depth understanding, micro-computed tomography was employed to analyse the 3D volume fractions of different hempcrete phases and the spatial distribution and orientation of hemp shivs in hempcrete. The results demonstrated that binder selection significantly affects the hempcrete performance. Among them, hempcrete with alkali-activated binder showed 4.1 times higher compressive strength and 30.9% lower thermal conductivity compared to hydrated lime binder; this was a very interesting result because higher mechanical strength typically correlates with increased thermal conductivity. This study found that the exceptional performance was caused by a denser mortar matrix with smaller and more horizontally aligned hemp shivs than other samples. • 3D hempcrete phases and hemp shives properties were analysed using micro-computed tomography • Hempcrete with alkaline-activated binder showed improved strength and thermal conductivity • Alkali activated binder led to denser mortar matrix with small and horizontally aligned hemp shives