Tire-road noise is aserious problem, butcan be significantly reduced by the use of porous asphalt concrete. Here, the sound absorption of the porous asphalt concrete is important and can be predicted by ground impedance models. Ye t, modeling porous asphalt concrete is complex, especially when nonlocal effects and scattering effects are considered. The objective of this research is to predict the sound absorption coefficient for athree-dimensional porous structure. The proposed solution is obtained using anovel modeling approach, in which the total solution of the sound field is found by combining the solutions of twosubsystems: abackground sound field and ascattered sound field. The background sound field contains the (analytical)solution of the sound field including the viscothermal energy dissipation inside the pores of the porous asphalt concrete. In the second subsystem, the (numerical)solution for the scattering on the rigid stone skeleton of the pavement is found. Forboth subsystems, we use amodel containing twolayers: an air layer and aviscous air layer with acertain granular structure. The main advantage of this modeling approach is the (relatively)l ow computation time. In this paper,the proposed modeling approach and the validation of this approach are described. The modeling approach is validated for normal incident plane wavesabsorbed and scattered by various structures of stacked marbles, using the impedance tube technique. This approach can be applied to predict the absorption coefficient of porous structures, likea sphalt concrete roads. Moreover, it can be used as design tool to optimize the sound absorption of newroad surfaces.

Tire-road noise is aproblem in many(densely)populated areas. It can be significantly reduced by using porous asphalt concrete. Achallenge is to develop porous asphalt concrete, such that the most dominant frequencies in tire-road noise will be absorbed by the road surface. It is especially important to also reduce and absorb oblique incident sound waves, since tires radiate noise normal to the tire surface, which means oblique incident waveson the road surface. Predicting the behavior of porous asphalt concrete using models is complex, especially when non-local effects and scattering effects are included. The objective of this paper is to showamodeling approach to predict sound absorption for oblique incident wavesinthree-dimensional porous materials. Using this method, one is able to predict the sound absorption of porous road surfaces in the design phase. This modeling approach includes at wo-step approach in which first the viscothermal energy dissipation inside the pores between the rigid materials (stones)a re estimated and then, secondly,the non-local effects such as scattering on the st ones within the porous road surface are computed using afinite element model. The combination of both sound fields givest he total sound field in and above the three-dimensional porous material, which is used to determine the sound absorption coefficient. The analytical viscothermal and scattering solution are discussed in this paper and the modeling approach is validated with experiments using ab ox with stacked marbles for several angles of incidence.

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