Study on sound absorption model of porous asphalt concrete based on three-dimensional morphology of air voids

In this paper, the authors are mainly committed to studying the influence of 3D morphology of air voids based on sound absorption performance of porous asphalt (PA) concrete. CT scanning technology was used to get the digital cross-sectional images of PA concrete samples, and image processing technology was used to identify air voids in all the digital cross-sectional images. Based on overlapping principle, sequential splitting theory was developed for searching and reconstructing the three-dimensional (3D) morphology of all the sound propagation paths in PA concrete samples. In order to reveal the sound absorption mechanism, a kind of equivalent hypothetical model consisting of tubes and cavities was proposed to predict the sound absorption coefficient of PA concrete. In the process, a decomposition method was developed to decompose sound propagation paths into tubes and cavities; Equations for calculating sound absorption coefficient were derived based on electric-acoustic analogy. The main conclusions: (1) Two-dimensional (2D) gamma dodging algorithm can greatly improve the accuracy of image segmentation; (2) There are 142.8e4, 156.6e4, 1168.2e4, and 2478.6e4 interconnected sound propagation paths that were found according to the sequential splitting theory in the Sample-I – Sample-IV, respectively; (3)The minimum sound propagation path length is generally more than twice the thickness of PA concrete samples, and maximum length even reaches more than 10 times the thickness; (4) With the increase of void content in PA concrete, the sound-absorbing frequency band will become wider, absorption peak will move to higher frequency, and the peak value of sound absorption coefficient will become larger; (5) There is a small difference between the test values and predicted values of sound absorption coefficient, except Sample-I, indicating that hypothetical PA concrete models can well explain the sound absorption mechanism of PA concrete; (6)For Sample-II to Sample-IV, the mean value of predicted sound absorption coefficient reaches 82.22%, 85.71% and 91.92% of test results respectively.