Spatial variability analysis of aged bridge concrete interfacial transition zone using 3D image scanning

This study employed core specimens taken from a 24-year-old concrete bridge to investigate the ITZ spatial variation. As the lowest hardness component in the concrete, the ITZ was determined by height differences with other components caused by polishing. An automatic method for identifying the ITZ was developed based on 3D images with horizontal and vertical resolutions 1.75 μm and 0.41 μm, respectively. The thicknesses of ITZ and height differences between ITZ and mortar were statistically analysed, and a copula joint distribution model was established to describe these characteristics. The results showed that thicknesses at beam end and midspan were 47.62 μm and 42.95 μm, and height differences were 24.38 μm and 19.98 μm, respectively, indicating that the ITZ degradation in beam end was more severe. However, the correlation coefficients for the joint distribution at beam end and midspan were nearly identical (0.7197 and 0.7111, respectively), showing a relative stable relationship between the ITZ thickness and hardness.