Characterization of the interconnected pore and its relationship to the directional permeability of porous asphalt mixture

Abstract

The efficiency of the water flow path (or the interconnected pore) within the porous asphalt (PA) mixture could affect the permeability performance significantly. This study aims to quantify the interconnected pore of the PA mixture and find the evidence for the relationship between the pore microstructure and the permeability performance. The laboratory experimental matrix includes six PA mixtures with air void content varying from 18.4% to 22.9% by altering the gradation, fiber contents and compaction levels. A self-designed directional permeability test was used to measure the permeability of the PA mixture in both vertical and horizontal directions. Industrial X-ray CT scanning and image analysis method were used to analyze the interconnected air void content (Vai) and average tortuosity (Ta) of the PA mixture in both horizontal and vertical directions. Results indicate that the self-designed directional permeability test could measure the vertical and horizontal permeability coefficient simultaneously. The vertical and horizontal permeability of the PA mixture are different. The PA mixture with addition of fiber presents the highest Ta and the PA mixture with under-compacted condition presents the highest Vai among the six PA mixtures. Based on the correlation analysis, it was found that the directional permeability of the PA mixture is influenced by the coupling effect of the Vai and Ta.