Experimental Study of the Dimensional and Hygrothermal Properties of Hemp Concrete under Accelerated Aging

Abstract

In this article, the functional properties of hemp concrete are studied. Hemp concrete stands to reduce the carbon impact and improve the energy consumption of houses. Hence, numerous properties are measured: mass and dimension (volume) variations are found, as is the variability in hygrothermal properties (density, thermal conductivity, heat capacity, moisture buffer value, and water vapor permeability). This entry proposes three different characterization campaigns. The first is a short introduction to the spatial variability in thermal conductivity; the second is dedicated to the study of univariate variations in the mass, volume, and hygrothermal properties of hemp concrete samples. The last one tackles the aging evolution of the properties characterized during the second campaign, in which the samples follow several aging protocols, including exposure to outdoor conditions, the application of immersion-drying cycles, and the application of freeze–thaw cycles. A set of samples is kept under control conditions to allow for comparison. As the main result, spatial variability was found in the material. This is related to the random manufacturing variability or the spatial position regarding the height of the manufactured element. A high univariate variability is found across hemp concrete samples. Moreover, the storage of samples under stable reference conditions implies very little change in the studied materials’ properties, whereas all accelerated aging protocols implied major changes of properties. In particular, we observed an evolution of the thermal conductivity of the samples kept under control conditions for 4 months, with the thermal conductivity ranging from −2.7% to +6.3% with a mean evolution of +1.22%. We observed an increase in the same property, ranging from +2.7% to +18.3%, with a mean of +9.0% for samples kept for 4 months under natural outdoor conditions, an increase ranging from +7.3% to +23.6% with a mean of +15.2% for samples that had undergone 20 cycles of immersion-drying, and an evolution of this property ranging from −5.6% to +12.3% for samples that had undergone 20 freeze–thaw cycles.