In order to meet the requirement of sustainable development, building materials are increasingly environmentally friendly. They can be partially or fully bio-based or recycled. This paper looks at the development of fully bio-based composites where agro-resources are valued as bio-based aggregates (hemp) and as binding materials (wheat). In a previous work, a feasibility study simultaneously investigated the processing and ratio of wheat straw required to ensure a gluing effect. In this paper, three kinds of hemp-straw composites are selected and compared with a hemp-polysaccharides composite. The gluing effect is analyzed chemically and via SEM. The developed composites were characterized multi-physically. They showed sufficiently high mechanical properties to be used as insulating materials. Furthermore, they showed good thermal performances with a low thermal conductivity (67.9–69.0 mW/(m $·$ K) at 23 ${}^{°}$ C, dry).

This 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.

An experimental and numerical study of internal laminar natural convection above horizontal wavy plates subject to a uniform and constant heat flux density is performed in this article. The flow movements are visualized by using the laser tomography technique. Surface temperature are measured by using the infrared thermography technique. Amplitudes and periods of the sinusoidal protuberances vary respectively from 6 to 24 mm and from 18 to 54 mm, and the modified Rayleigh numbers vary between 10 6 and 4 2 10 8 . Two structures of the flow movement are noticeable. They are respectively characterized by the presence or by the absence of recirculating movement of the air above the heated plate. The occurrence of each type of structure is correlated with the surface parameters and with the modified Rayleigh number values.

The classical models describing hygric transport inside building materials seem unsuitable for bio-based materials. Based on the assumption of an instantaneous local equilibrium between relative humidity and water content evolving according to the sorption isotherms, they predict much shorter stabilisation times than those obtained experimentally. A new approach is presented here: it frees from the local instantaneous equilibrium by introducing local kinetics to describe the transformation of water from the vapour state to the absorbed liquid state and vice versa. In the framework of the European IsoBio project, a multilayered wall mainly made of bio-based materials was developed. The different layers were characterised in terms of sorption, vapour permeabilities and thermal conductivities. The sorption measurements performed on representative samples allowed determination of the local kinetic constants. The hygrothermal behaviour of the test wall was then studied in an instrumented demonstrator (Hive, Wroughton, UK). The recorded measurements were compared with simulations based on the instantaneous local equilibrium model (TMC code) and on the local kinetics of sorption model (TMCKIN code). TMC very significantly underestimated the dynamics of the local relative humidity variations whereas TMCKIN succeeded in predicting these dynamics and produced results close to measurements.