Meso-scale damage detection and assessment of concrete under dynamic compression loading using X-ray computed tomography

Extraction of effective and discriminative meso-scale damage evolution information from concrete CT test results is great significance because it is critical to predicting and understanding the complex meso-scale damage behavior of concrete material highly linking to their complex meso-scale structures. This research mainly focused on the following three aspects: (1) Concrete CT tests were performed to obtain real-time scanning CT images of concrete specimen under dynamic compression loads. The meso-scale damage information contained in CT images was extracted for investigating the meso-scale damage evolution characteristics, (2) A new zoning method for concrete meso-scale damage was proposed by analyzing the change characteristics of CT number in CT images with different stress stages. Meso-scale damage was divided into visible and invisible meso-scale damage by using the new zoning method. Moreover, visible and invisible meso-scale damage were respectively defined as the meso-scale damage outside the transition region (MD-OTR) and meso-scale damage inside the transition region (MD-ITR), and (3) Changes of MD-OTR during dynamic compression loading were elucidated by using crack morphologic parameters, such as porosity, crack length, crack density, and crack tortuosity. The evolution characteristics of MD-ITR were investigated by analyzing the statistical feature parameters including contrast, energy, and homogeneity. Results shown that the corresponding porosity gradually increased at the middle-upper part of the specimen and it remained constant at the middle-lower part with increased dynamic compression load. Length, tortuosity, and density of crack presented a Gaussian distribution along the direction of the specimen height after specimen failure. In addition, contrast, energy, and homogeneity revealed different evolution rules at different specimen heights. For example, contrast increased linearly with the increase of dynamic load at H = 20 and 60 mm, but it firstly decreased and then increased at of H = 40 and 80 mm. Noteworthy, statistical feature parameters were more sensitive to stress changes before peak strength than the porosity, which is due to porosity depending heavily on the binary images of CT images ignoring the MD-ITR.