Influence of binder on the multiscale properties of hemp concretes

Abstract

Biobased materials are increasingly being used for building insulation. Hemp concrete is an efficient thermal insulation material containing renewable resources, providing living comfort thanks to its acoustical and hygrothermal properties. In this study, two hemp concrete ‘wall’ formulations are manufactured with the same type of hemp shiv and two commercial binders: natural cement and a lime-based formulated binder. Ninety days of curing (65% RH – 20 °C) ensure the hardening of the materials. Mortars are made up simultaneously to control the behaviour of the binders. The influence of binders on functional properties of hemp concretes and the relation with their microstructure are investigated in this article. The two materials exhibit similar thermal conductivity, acoustic performances and hydric properties, linked to their similarities considering density, open porosity, air resistivity, specific surface area and pore size. However, several other parameters describing the microstructure of the concretes are different depending on the binder, such as interparticle porosity, intra-porosity and tortuosity. Both formulations have low compressive strength compared with hemp concretes analysed in other studies. In our case, hydration of binders does not appear to occur. This could be due to an impact of the shiv extractible compounds on the hydration of the mineral binders.