Innovative low noise surfaces : comparison of damping and absorption

While sound absorption is an acoustic related prope rty reasonably well known and currently used to characterize low noise surfaces, damping is a prope rty commonly used in other domains to define the en ergy dissipation of a material but rarely used to charac terize this important mechanism in road pavements. This paper compares noise related properties such as dam ping and absorption of five road pavement surfaces. Two of which are innovative and therefore expected to b e low noise since they have high voids content, incorporate fine grading aggregates and expanded cl ay. Other two incorporate rubber and waste high-den sity polyethylene giving them an elastic and stiff behav iour respectively. The fifth is a conventional mate rial, asphalt concrete, used for control. Sound absorptio n tests and mechanical impedance tests were carried out in 30x30 cm slabs at 20oC. To measure absorption, an i mpedance tube with an open end was put on the surfaces. To determine damping, the response of a hammer impact measured by an accelerometer on suspended slabs was analysed. Results show that the innovative surf aces have better acoustic related properties while the surface with high-density polyethylene provided the worst results. Furthermore, a strong correlation o f damping and air voids was found.