Comparative study on the meso-scale damage evolution of concrete under static and dynamic tensile loading using X-ray computed tomography and digital image analysis

Abstract

A comparative study on the meso-scale damage evolution of concrete specimens was conducted through coupling concrete CT test and digital image analysis technology to investigate the deterioration properties of concrete material under static and dynamic tensile loading. The content of this research program mainly includes: (1) use of concrete CT test to acquire CT images containing the information of meso-scale damage evolution in concrete specimens under static and dynamic tensile loading modes; (2) use of digital image analysis technology to extract quantitative indications for assessing the differences of the initial meso-scale defects distribution and the differences of meso-scale damage evolution in concrete specimens under two different loading modes; (3) use of representative concrete cross-sectional CT images to analyze the differences of local meso-scale damage evolution and predict the fracture location of specimens; and (4) use of the air voids fraction to calculate the degree of meso-scale damage for investigating the differences in the spatial distribution of meso-scale damage under different deformation levels. Results showed that the meso-scale defects of heterogeneous concrete specimen could be identified on the basis of the relative grayscale values of CT images and could be characterized by quantitative indicators, such as aggregate fraction, mortar fraction, air voids fraction, and the mean and variance of the CT number. A comparison of the meso-scale damage evolution in concrete specimens under two different loading modes showed that the specimen subjected to dynamic tensile loading was first compacted, then expanded, and finally destroyed. By contrast, the specimen subjected to static tensile loading gradually failed as the load increased, and without exhibiting compaction. Moreover, the analysis of local meso-scale damage evolution contributed to predicting the fracture location of concrete specimens. The changes of degree of meso-scale damage clearly showed that the meso-scale damage is continuously distributed along the height of specimens, and its increment in each cross section is different under the same deformation condition. These proposed indicators are effective in analyzing the changes in the meso-scale damage of concrete. Among them, the air voids fraction and aggregate fraction are positively correlated with the CT number variance and CT number mean, respectively.