Hysteresis phenomenon in hemp concrete
Hemp concrete participates in a process of sustainable development in the housing field by reducing environmental impact and improving hygrothermal comfort. This kind of hygroscopic bio-material is characterized by a strong hysteretic hydric behavior. At a given relative humidity, hysteresis results in more or less differences between the equilibrium moisture content obtained during adsorption or desorption. This phenomenon affects moisture transfer in hygroscopic building materials. In this paper, experimental and numerical study on hysteretic behavior of the hemp concrete sorption process is presented. Experimental intermediate scanning curves are measured using the glass jar method. This experimental data is used to fit hysteresis models. In this study, one hysteresis model is selected for its suitability to represent the hysteretic hydric behavior of hemp concrete. It is based on the knowledge of the main adsorption and desorption curves respectively built from the dry to the saturated state and from the saturated to the dry state. Nevertheless, as for many porous biomaterials, the saturated state is difficult even impossible to reach. In order to overcome this issue, an original approach is presented leading to the identification of the main desorption curve from a primary desorption curve. The implementation of a suited hysteresis model in a heat and moisture transfer model allow evaluating and discussing the influence of this phenomenon in the transient hygrothermal response of hemp concrete to hydric loadings as on the sample scale as on the wall scale.