Measurement of sound absorption of wood chip-based materials for noise barriers: effects of testing and casting conditions

The territories characterized by a large woodland area, offer considerable potential for the development of a wood supply chain based on principles of circular economy and sustainability. However, there are limited products and applications of virtuous processes for the valorization of local materials with an optimized acoustic performance. This work focuses on recycled and reused by-products as a secondary raw material for the implementation of acoustic materials for noise barriers applications. Different typologies based on the use of loose wood chips (WCh), stone sawing waste (SS) and their combination in mix designs (WChS), where the WCh has been used as an aggregate, have been investigated. Sound absorption measurements were conducted on cylindrical samples in an impedance tube and on larger samples in a small-scale reverberation room (SSRR). The work analyzed the variability of the sound absorption coefficients in terms of reproducibility due to the loose material selection, mix design casting and testing methods. Experimental results demonstrated that the variability of the sound absorption of the WCh samples are affected mainly by the measurement method, while the WchS samples are significantly affected by the sample size, the mix design casting conditions, and measurement method.