沥青混合料三维空隙形态特征评价方法及分析

为了给沥青混合料细观特征研究提供空隙特性评价方法，实现空隙三维形态特征的描述，基于X-ray CT技术提取了沥青混合料空隙的三维结构，以空隙断面形心作为骨架节点，构建了三维空隙骨架模型；以骨架走向和断面形状为主要评价对象，建立了空隙形态特征的评价方法，提出了垂面内方向角、相邻垂面夹角、断面圆度以及断面丰度作为空隙形态的评价指标；以实验室成型的沥青混合料试件为研究对象，指明了空隙尺度、成型条件以及混合料级配（包括AC，SMA以及OGFC级配）对空隙空间形态的影响规律。结果表明：空隙形态特征评价方法可以反映空隙的三维形貌；空隙体积小于5 mm³的微细空隙接近于椭球形，大于5 mm³的结构空隙不规则程度较大；沥青混合料的成型方式与压实程度对空隙的形态特征无显著影响，其特征值分布曲线的均方根偏差均低于1.2%；OGFC级配下微细空隙相较其他2种级配更加圆润，丰度为0.9~1.1处的分布频率比其他2种级配高出19.2%，圆度在大于5区间的分布频率高出14.9%；结构空隙中，AC级配的垂面内方向角分布曲线在80°~90°区间内高出OGFC级配5.3%；AC级配的空隙骨架最为迂曲，不规则性最强，而OGFC级配的空隙骨架比较顺直。

Investigation and Characterization of 3D Void Mesostructures in Asphalt Mixtures

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.