Water movement and diffusion in wood is a well-documented research topic. It is strongly linked to the physical and mechanical properties of wood, and thus it has a high degree of importance and prominence for real-life application, particularly in wood drying. Here we employed the terahertz (THz) spectroscopy and imaging techniques to study the diffusion of water in wood. For our first experiments, we used balsa, a species of wood with a relatively homogenous structure (at the tissue level) and a low density that turns into fast diffusion rates and low absorption of the terahertz beam. This enables us to conduct several consecutive observations from various conditions (angles, diffusion directions, etc.) in a short time. These preliminary studies confirm the feasibility of terahertz spectroscopy and imaging techniques as a tool to observe the water diffusion in wood as a function of the direction (Fig. 1). We have also measured the evolution of the attenuation coefficient of the terahertz beam on wet and drying wood at different times. A model of the diffusion behavior based on these measurements, and according to the water content, will be developed and compared with other conventional water diffusion models based on gravimetry methods for the identification of the diffusion coefficients.

The influence of an Interfacial Transition Zone on mechanical behavior of concrete has been established by many authors. Several experimental studies have highlighted the weak mechanical properties of Interfacial Transition Zone due mainly to higher porosity than other phases, or to the presence of initial damage at the interface between paste and aggregates. Thus, it is necessary to take this zone into account when modelling the mechanical behavior of concrete, particularly outside of the elastic domain. Various analytical or numerical methods have been proposed, and some of these replace the physical representation of an Interfacial Transition Zone, by an imperfect interface between paste and aggregates, and an adhesion model with specific mechanical properties. In this work a cohesive zone model coupling adhesion, friction and unilateral contact is applied to a finite element model of a cement paste-aggregate composite, designed to test interface mechanical properties. Cohesive zone model parameters are calibrated using an experimental study of the same composite, submitted to mechanical loading during hydration and leaching of cement paste. This numerical approach allows modelling of the mechanical behavior of a composite until the tensile strength is reached. Moreover evolution of cohesive zone model parameters during hydration and leaching, shows a partial adhesion on contact surfaces between cement paste and aggregate. This could explain initial interface damage.