Hygrothermal effects and moisture kinetics in a bio-based multi-layered wall:Experimental and numerical studies

International audienceA bio-based multi-layered reference wall has been developed within the framework of the European ISOBIO project. One of the key points of this project was to be able to perform proper simulations of the hygrothermal transfers occurring inside such walls. Previous published investigations, also performed in the framework of this project, have demonstrated that the classic assumption of instantaneous equilibrium between local relative humidity and water content according to the sorption isotherm is not relevant for bio-based porous materials, where, in practice, a rather slow kinetics of sorption occurs. The theoretical background developed in this previous study is used here to determine the kinetic constants of the bio-based construction materials and to perform 1D hygrothermal simulations. The kinetics constants are determined thanks to a 1D cylindrical tool based on the local kinetics approach, validated against several experiments of sorption. Then, heat and hygric transfers recorded on a demonstrator building (The HIVE, Wroughton, UK) are analyzed and are simulated using two modeling tools: TMC based on the Künzel approach and TMCKIN based on the local kinetic approach. From the simulations, the local kinetics improves the small timescale RH dynamics. The comparison with measurements performed in the demonstrator confirms the relevance of the local kinetics approach

Mechanical properties of hemp-clay and hemp stabilized clay composites

International audienceThis study aims to develop a new low carbon footprint material using hemp and clay. It investigates the effect of clay stabilization and hemp to binder ratio on mechanical performances. All composites have ductile behavior. Composites with highest hemp to binder ratio show steadily increasing strength with deformation. Hemp stabilized clay composites have better mechanical properties than hemp clay composites. Mechanical properties strongly depend on the hemp to binder ratio. The tensile strength ranges from 0.021 to 0.059 MPa. The compressive strength ranges from 0.39 to 0.68 MPa. The mechanical performance of developed composites meets the requirements of the intended use. © 2017 Elsevier Lt

Effect of hemp content and clay stabilization on hygric and thermal properties of hemp-clay composites

International audienceThe objective of this paper is to investigate the effect of clay stabilization and hemp content on hygric and thermal performances. This experimental study is based on the measurement of sorption isotherm, moisture buffer value and thermal properties. The effect of water content on thermal conductivity is also investigated. The results show that Hemp Clay Composites (HCC) and Hemp Stabilized Clay Composites (HSCC) are hygroscopic and moisture buffering materials. The correlations between hemp content and water content are identified for sorption curves. An innovative analysis of the contribution of hemp and binder to water sorption is performed. The moisture buffer values classify the designed composites as excellent hygric regulators according to the Nordtest classification. The thermal conductivity ranges from 0.089 to 0.120 W/(m.K) at dry state, making them suitable for distributed insulation. The thermal conductivity increases linearly with density, for the two binders investigated in this study. Besides, the thermal conductivity increases linearly with water content too. Finally, this study underlines that the designed composites show high hygrothermal qualities

Réduction du pouvoir absorbant de chènevottes par traitement imperméabilisant

Le béton de chanvre est utilisé comme matériau de remplissage non porteur associé à une ossature bois. C’est un matériau composite obtenu en mélangeant un liant minéral à base de chaux, du chanvre (chènevottes) et de l’eau. Afin de garantir une bonne mise en œuvre, le béton de chanvre a, en général, un besoin en eau de gâchage nettement supérieur à celui d’un mélange classique granulat/liant. Cette quantité d’eau est de plus liée au process de fabrication. Cette étude vise à montrer l’influence de la chènevotte sur le dosage en eau et à évaluer les effets d’un traitement visant à réduire la capacité d’absorption de la chènevotte tout en préservant au maximum les propriétés qui font du béton de chanvre un bon matériau isolant et perméable. Un banc expérimental est conçu pour réaliser les essais de mouillage. Différents protocoles de traitements par immersion avec un hydrofuge sont testés

Variation des propriétés thermiques de bétons de chanvre en fonction de la formulation

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Experimental Investigation of Air Conditioning in a Bi-climatic Room

International audienceThis paper is a preliminary study to the investigation of hygrothermal behavior of wall implemented as separating wall of bi-climatic rooms. One room simulates indoor environment while the second simulates exterior climatic solicitations (temperature and relative humidity). Four typical Tunisian winter climate are selected for this study. The aims are to check the homogeneity of ambient conditions in the rooms, the reaching of the set point, the delay to reach it after setting then if the ambient conditions remain constant once they are reached, and finally the response time of the whole system. The results underline that some climate are easy to reach while other may be difficult to obtain due to competitions between climatic systems. This may be solved by acting on the device management. The typical response times are short enough to plan daily cyclic variations in the following steps of the study and ambient conditions are homogeneous in the room. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG

Development and hygric and thermal characterization of hemp-clay composite

International audienc

Hygrothermal Behavior of a Washing Fines-Hemp Wall under French and Tunisian Summer Climates: Experimental and Numerical Approach

International audienceThis study experimentally and numerically investigates the hygrothermal behavior of a wall made of washing fines hemp composite under typical French and Tunisian summer climates. Actually, insulating bio-based building materials are designed in order to reduce energy and non-renewable resources consumptions. Once their multiphysical properties are characterized at material scale, it is necessary to investigate their behavior at wall scale. Washing fines hemp composite shows low thermal conductivity and high moisture buffer ability. The test wall is implemented as separating wall of a bi-climatic device, which allows simulating indoor and outdoor climates. The numerical simulations are performed with WUFI Pro 6.5 Software. The results are analyzed from the temperature, relative humidity and vapor pressure kinetics and profiles and from heat and moisture transfer and storage. The thermal conductive resistance calculated at the end of the stabilization phase is consistent with the theoretical one. The hygric resistance is consistent for simulation up to steady state. The dynamic phase under daily cyclic variation shows that for such cycles two thirds of the thickness of the wall on the exterior side are active. It also highlights sorption-desorption phenomena in the wall

Variation des propriétés thermiques de bétons de chanvre en fonction de la formulation

National audienc