Sound absorbing plaster based on natural fibres: experimental investigation of the correlation between formulation components and acoustic properties

Controlling reverberation and reducing noise in medium to large rooms represents one of the greatest architectural challenges today. Several solutions are currently available so that spaces can be acoustically engineered by including measures that make the acoustics of the same environment optimal and positively affecting health and wellbeing of people living in. This means that a compromise between room design and acoustic specification of employed systems is required. Currently, BASWA acoustic works in such direction, providing high-quality acoustic systems whose technology combines functionality and aesthetics, being adaptable to any type of environment. Next to its own standard products commercially available, the company is also involved in setting new acoustic systems to broaden its gamma and provide emerging markets clients with performing design options. An example is given by the research project, named EQ Project, which this Master Thesis work is associated to. In detail, the EQ project is designed to develop an economically competitive sound absorbing system in emerging markets where the price of BASWA standard acoustic systems does not allow them to compete with other manufacturers ones who sell their cheap but low technically level products. The goal is to guarantee the customer a simple, easy-to-install and high-quality system, resulting from the know-how the company has acquired over time. In this perspective, this Master Thesis research work was carried out. The main objective of this study was to develop an acoustic plaster based on organic aggregates, as cellulose, in combination with additives and a formulation of organic/inorganic binders. After defining properties according to beforehand established specification, different formulations were developed. They were tested to investigate their own sound absorbing properties and to understand the relationship between physical parameters and acoustical performance. The acoustic characterization was feasible by employing the Impedance Tube (IT) method, which is a standardised measurement technique, and the Small-Scaled Reverberation Room (SSRR), located at Politecnico di Torino. Both were chosen to determine the sound absorption coefficient, that is one of the most representative parameters defining the sound absorbing material quality as it can measure the quantity of the sound energy absorbed from the tested sample to the ones hitting its surface. On the other hand, Scanning Electron Microscope (SEM) technology was used to analyse the inner open-pore structure features of the sound absorbing coating in order to relate it to the sound absorbing properties. The data obtained proved that components in plaster formulation, such as inorganic fillers and different binder ratios, affected the plaster acoustic properties. In addition, it was shown that sample mounting and fixing conditions during the impedance tube measurement had a strong effect on the determination of the sound absorption coefficient. Thus, such experimental results can be considered as initial guidelines in choosing prototypes as potential acoustic systems aimed to the EQ Project as well as an interesting starting point for research and development in sound solutions whose absorption performance could be connected to their mix design characteristics.