Abstract:

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.

Key words: crack evolution, multi-field coupling, pavement concrete, image segmentation, dynamic damage, de- veloping rule