Acoustic properties of porous concrete - Experiments and modelling

The main objective of this work is to characterize, experimentally and theoretically, the acoustic performance of porous concrete mixtures and their macroscopic parameters. The aggregates used in the mixtures were expanded clay with different grain sizes and lava. Both sound absorption coefficient and surface impedance were measured in an impedance tube, so that it was possible to identify the influence of the size and shape of the aggregate grains and the water/cement ratio have on the sound absorption capacity of the samples. Subsequently, a theoretical model proposed by Horoshenkov and Swift [1] was used to determine the sound absorption coefficient and surface impedance of porous samples based on macroscopic parameters. The parameters considered were porosity, airflow resistivity, tortuosity and standard deviation of the pore size, of which the last three were determined both experimentally and by an inverse method, while the first one was determined experimentally. Either use the experimental data or use the theoretical data it becomes possible to represent these materials in numerical models as equivalent fluids. The different approaches, experimental and theoretical, were compared in order to perceive how much the theoretical model fits the experimental data. Keywords: sound absorption, porous materials characterization, impedance tube, inverse method