The dynamics of water content in the superficial layers of soils is critical in the modelling of land-surface processes. In arid regions, vapour flux contributes significantly to the global water mass balance. To account for it in theoretical descriptions, most of the models proposed in the literature rely on the local equilibrium assumption that constrains the vapour pressure to remain at its equilibrium value. It implicitly amounts to consider an instantaneous phase change. Recent works underlined a retardation time and a decrease in phase change rate as the water content gets lower. Therefore, the objective is to revisit water transport modelling by rejecting the local equilibrium assumption. This requires developing a non-equilibrium model by taking into account the phase change kinetics. To assess the interest of this approach, a natural soil of Burkina-Faso has been experimentally characterized from independent tests and soil column experiments have been carried out. The comparison of experimental drying kinetics and water content pro

Interpreting the drying kinetics of a soil using a macroscopic thermodynamic non-equilibrium of water between the liquid and vapour phase A. Chammari (a) , B. Naon (b) , F. Cherblanc (a) , B. Cousin (a) and J.C. Bénet (a)

Unsaturated soil hydraulic properties are key properties in the fields of soil science and civil engineering. Because of their strong dependence on water content, there are considerable experimental and numerical difficulties in their determination, specifically in the dry range. This situation is encountered regularly in arid and semi‐arid regions. The models commonly used for predicting the unsaturated hydraulic conductivity function rely on pore bundle concepts that account for capillary flow only and neglect film flow. Furthermore, the assumption of a local equilibrium between liquid water and its vapour is no longer valid at small water contents. Thus, with classical approaches, the experimental identification of hydraulic characteristics can fail at small water contents. To emphasize the weakness of capillary models, soil column experiments have been carried out with two sandy soils from Burkina Faso. Special care was taken to prevent any transport processes that are not directly related to liquid transport. Data from profiles of water content were used in an inverse numerical procedure to identify the coefficients of a new relative hydraulic conductivity function. Our results show that this simple approach is suitable for the analysis of flow processes at small water contents. It provides a simple, robust and inexpensive method to identify the properties of the unsaturated conductivity function that account for capillary and film flows. Highlights A new kind of soil column experiment is proposed to focus on the dry range. A new relative hydraulic conductivity function accounting for film flow is introduced. The weaknesses of classical relative hydraulic conductivity functions are emphasized. It provides a simple, cheap and robust method to identify the relative hydraulic conductivity.

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The present study aims at valorizing two residues types of the foodless vegetable biomass which are abundant and very pollutant in Burkina Faso. To do it, first we try to identify the optimal values of chipboard elaboration parameters with kenaf and cotton stems by using a natural binder (the bone glue). Next we proceed to the elaboration of two panels types with optimized elaboration parameters. Besides we determine mechanical and thermal characteristics of elaborated panels with a view of an indoor thermal insulation application. Also it becomes necessary for us to determine by experimenting the thermal conductivity, Young's modulus, Coulomb's modulus, and the water inflation rate, taking into account some elaboration parameters on one hand and the correlation between mechanical and thermal properties on the other hand. Finally, the obtained results are compared with the panels properties values required by ANSI A 208.1-1999 standard.