Microscopic hydric characterization of hemp concrete by X-ray microtomography and digital volume correlation

Hemp concrete is a bio-based material used in buildings construction. It presents particularly interesting hygrothermal properties. This very heterogeneous material is constituted by hemp particles embedded in a mineral binder. This paper focuses on the microscopic and hygromorphic characterization of hemp concrete based on non-destructive imaging techniques. X-ray tomography scans with different voxel sizes were performed on this material. The reconstructed volumes had a mean voxel size between 2.3 µm and 31.8 µm. 3D reconstructions of the real material showed that hemp concrete has several scales of porosity which depends on the orientation and position of the plant particles. Then, a tomography scan and SEM observations were made on the vegetable particle. The latter presents a complex and very porous microstructure. The hygromorphic behavior of hemp concrete under hydric solicitations was then studied. The technique consists in using X-ray tomography coupled to the digital volume correlation (DVC) to determine the three-dimensional strain fields in the studied three-dimensional volume. The results show a change in the internal morphology of hemp concrete subjected to different hygrometries. The humidification of the material leads to the appearance of anisotropic strains in the 3D volume. The strains of the hemp particles are greater compared to those of binder. In addition, the swelling of the hemp shiv causes the reduction of the porous space between the binder and the plant aggregates called interparticle porosity.