Hygrothermal behaviour of a hemp concrete block, experimental and numerical results

Abstract

Most building materials, and more particularly bio-based materials, are subjected to hygrothermal transfers in the environment in which they are disposed. These transfers depend on the thermophysical characteristics and the ambient humidity and temperature conditions. In this environment and despite these variations, the material must be able to ensure in a sustainable manner, the functions for which it was implemented (thermal, mechanical, acoustic ...). In this paper we treated the coupled heat and mass transfer within bio-based building material problematic. We have chosen the hemp concrete and we proceed as follow: a thermophysical characterizations are done, in order to obtain the thermal, hygroscopic and physical properties of hemp concrete. These values are then used as input parameters for a numerical modelling. Philip and De Vries mathematical model which predicts heat and mass transfer within porous media is implemented. The model takes into account thermal and hygric transfer phenomenon. For the purpose of the model validation, experimental facility is carried out, which consist of monitoring a sample made of hemp concrete. The temperature and relative humidity are recorded with temperature and humidity sensors placed at the interface and inside the material. The sample is positioned into the wall of laboratory, in order to separate the inside and the outside conditions. The sample is submitted to real indoor and outdoor ambient conditions. We aim to investigate the hygrothermal behaviour of hemp concrete and observe its response versus ambient variation on the one hand, and to assess the mathematical model’s ability to predict the hygrothermal behaviour on the other hand. The experimental and the modelled results are compared and then discussed.