Microstructural investigation on air void properties of porous asphalt using virtual cut section

•A research framework for virtual cut section analysis on porous asphalt mixture.•Polar diagram is used to complement the conventional cross-section analysis.•Air voids shape in porous asphalt are predominantly elongated.•Recommend Fmax parameter in determining air void size of porous asphalt. The microstructure properties of asphalt mixtures reflect the structural and functional performance of asphalt mixtures. Thus, numerous imaging methods are developed including destructive and non-destructive methods to uncover the internal structure properties of asphalt mixtures. However, accurate analysis of internal microstructure properties is challenging. This study used a non-destructive method employing virtual cut section (imaging technique) to analyze the air void properties of laboratory-fabricated porous asphalt. Conventionally, the investigation of internal structure properties particularly on vertical section requires the sample to be cut (destructive method) into several sections. This method causes defects to the sample and limits the amount of data that can be extracted from the image. The imaging technique designed in this study provides comprehensive understanding of the distribution and properties of air voids from different angles within the compacted sample of porous asphalt. The void properties in porous asphalt should be assessed accurately to ensure effectiveness of water permutation through the porous structure and acoustic function of the mixture. The compacted samples were X-rayed and virtually analyzed into various cut sections. The void properties were characterized in terms of the content, number, shape, and size of voids. Results indicate that air voids within the porous asphalt are homogeneously distributed with an elongated shape; this characteristic indicates high void connectivity. The vertical cross-section analysis justifies the characteristics of air voids in the conventional analysis of horizontal cross section.