New thermal regulations are currently implemented in buildings in order to save energy, leading to new kinds of materials. However, noise annoyance should not be neglected. Materials based on plant particles and fibers, such as hemp concrete and hemp/flax wools, are characterized by high-level multifunctional properties and are suitable solutions in this context. The aim of this thesis is to investigate the acoustical properties of these materials, and to highlight their multiscale behaviour. For this purpose, the physical and acoustical properties of plant wools, shiv and hemp concretes were characterized, and analyzed using the theory of acoustics in single and multiscale porous media. Our experimental program showed that the high-level acoustical properties of these materials can be controlled by the characteristics of their constituents and their manufacturing process. It is further highlighted that, given the permeability contrast existing between micropores (intrafiber, intraparticle, and intrabinder pores) and mesopores (interfiber or interparticle pores), only mesopores do take part in the acoustical dissipation. In this context, semi-phenomenological models have been used to predict the acoustical properties from the basic parameters of wools, shiv and hemp concretes. This model is finally used to show that the acoustical properties of these materials can be optimized using their formulation, multilayer structure and surface geometry ; and to realize a quality check of hemp aggregates characteristics.
Acoustics of Building Materials based on Plant Fibers and Particles : Tools for Characterization, Modelling and Optimization