Sound absorption characteristics of surface perforated mortar with micro-sized pores

Abstract

Surface perforated mortar (SPM) is a cement-based acoustic material that can reduce railway noise. SPM has macro-sized holes on its surface, and the geometry of the holes influences the majority of the absorption performance of SPM. A previous study achieved a higher sound absorption performance than that of traditional pervious concrete by attenuating the resonance caused by the holes. Given that most of the acoustic materials are porous, it was hypothesized that micro-sized pores can enhance the sound absorption performance of SPM. Therefore, this paper exploits aluminum powder as a foaming agent for cement and investigates the effect of the micro-sized pores on the sound absorption of SPM. An in-situ sound absorption test results revealed that incorporating micro-sized pores in SPM improves the sound absorption performance by 133%. The frequency range of sound absorption is mainly dependent on the geometry of the macro-sized holes, and the amount of micro-sized holes affects the degree of sound absorption. Based on the experimental studies on the effects of the geometry of the macro-sized holes and the amount of the micro-sized holes, the design guidelines for SPM are proposed.