Three-dimensional characterization of air voids in porous asphalt concrete

Abstract

In this paper, a porous asphalt (PA) concrete specimen is taken as the research object to study the three-dimensional (3D) characterization of air voids in PA pavement. The digital cross-sectional images of the specimen were obtained by computed tomography (CT) scanning technology. Based on image processing technology and OTSU method, the voids were identified and separated from cross-sectional images and CT images were divided into three parts: void, asphalt mortar and aggregate. The 3D geometry of pores in the specimen was successfully reconstructed by 3D reconstruction technology proposed according to the overlapping principle. In order to obtain more accurate void size, a modification method was developed to reflect its actual value, and the topological structure of pore structures was studied at last. The main conclusions are as follows: (1) If necessary, image dodging should be conducted to uniform the illumination of CT images before segmentation, which may make a positive contribution to the segmentation results; (2) Pore structures in PA pavement can be divided into three types according to its interconnectivity with the external space, namely, interconnected pore, semi-interconnected pore and closed pore. (3) According to overlapping principle, pore structures can be reconstructed and separated into single pore with void images deducting those covering texture depth. (4) The 3D geometry of pores is complex and disordered, and the direction goes different, indicating that void size obtained from void images is generally larger than the actual size. (5) The actual size of voids in specimen is mainly distributed below 4.13 mm, mainly in the range of 1.03 ~ 1.55 mm and adjacent ranges.