沥青混合料三维空隙形态特征评价方法及分析

To investigate the morphological characteristics of 3D voids in asphalt mixtures that contribute to the micro structure study of asphalt mixtures. The X-ray computed tomography (CT) system was utilized to scan and capture the 3D void structure in asphalt mixtures. The void frame model was developed with a method that considers the centroid of the void slice as the control node of the frame network. Based on the frame model, the direction of the void frame and shape of the void slice were discussed. The evolutional method of 3D void morphological characteristics was developed and indices including direction angle, vertical planes intersection angle, fullness ratio, and roundness ratio were given. The asphalt mixture samples produced in the laboratory with a varied compaction methods, compaction times, and asphalt mixture types including asphalt concrete (AC), stone matrix asphalt (SMA), and open graded friction concrete (OGFC) were considered and the contact relation of these factors with the morphological characteristics of 3D voids was analyzed. The results show that the evolution method can well characterize the 3D void morphology. Small void shapes with a volume of less than 5 mm³ are close to the ellipsoid. The larger void shapes with a volume greater than 5 mm³ are more irregular. The compaction condition of asphalt mixture is not a sensitivity factor to void morphology. The root mean square error (RMSE) of the indices among different compaction conditions is under 1.2%. The small void shapes in OGFC samples are closer to globular compared to the other two grades. In OGFC samples, the fullness ratio in an interval of 0.9 - 1.1 and roundness ratio in an interval of 0.8-1.0 are 8% and 5% higher than that in the other two grades. For larger voids with a volume greater than 5 mm³ in the AC grading, the direction angle in an interval of 70° -90° is 5% higher than that in the OGFC grading. It shows that the voids in AC samples are tortuous and irregular, whereas those in OGFC samples are straight and smooth.