细观裂缝的演化与空间展布规律是影响路面混凝土耐久性的关键因素． 为明确 寒冷地区路面混凝土在实际工作环境下结构内部微裂缝的萌生、扩展、压缩等演化规律， 基于多场疲劳试验，针对路面混凝土内部结构进行了 SEM、CT 扫描及图像分割，通过对比 分析荷载单场、荷载 － 冻融双场及荷载 － 冻融 － 干湿循环三场耦合下的裂缝面积密度、平 均裂缝宽度、最大裂缝长度及盒分形维数特征，从细观尺度揭示了不同荷载水平、耦合方 案下微裂缝的动态损伤发展规律． 结果表明:单荷载作用下，随荷载次数增加，最大裂缝长 度呈萌生 － 闭合 － 延伸交替变化，宽度表现为压缩 － 扩张交替变化，分形维数先增后减; 荷载 － 冻融双场耦合引发的结晶膨胀应力促使裂缝面积密度及最大裂缝长度单调增加， 80%荷载水平时，混凝土在较小裂缝长度、宽度下便发生疲劳破坏;荷载 － 冻融 － 干湿循 环三场耦合下，附加干缩应力沿裂缝方向产生收缩应力，在垂直裂缝方向产生压缩应力， 促使裂缝沿长度方向延伸，宽度减小，同时伴随更多微裂缝成核．

The evolution and spatial distribution rule of microcosmic cracks are two key factors affecting the durabi- lity of pavement concrete.In order to explore the evolution of microcracks initiation,propagation and compression for pavement concrete in actual working environment in cold regions,multi-field fatigue tests were conducted,and SEM,CT and image segmentation techniques were adopted to compare the crack characteristics such as area densi- ty,average width，maximum length and fractal dimension for specimens respectively in a single field,in double fields and in three-field coupling condition.Then,the dynamic damage rules of microcracks under different loading levels and with different coupling schemes were discussed in meso scale.The results show that (1) under the ac- tion of single load,the maximum length of cracks shows a“initiating-closing-extending”trend,while the average width reveals a“compressing-expanding”trend,and the fractal dimension first increases and then decreases with the increase of loading cycles; (2) the crystallization swelling stress initiated by loading-freezing-thawing coupling effect makes the crack area density and the maximum crack length both increase,and the concrete reveals fatigue failure with small crack length and width under 80% loading condition; (3) under the loading-freezing-thawing- wetting-drying three-field coupling condition,the additional dry shrinkage stress causes a shrinkage stress in the parallel direction of the crack and a compressive stress in the vertical direction of the crack,which makes the crack length increase,the crack width decrease,and more micro-cracks nucleate.