CT OBSERVATION AND INTERNAL 3D DEFORMATION CALCULATION OF CONCRETE UNDER UNIAXIAL COMPRESSION

A concrete specimen under uniaxial compression was scanned by using Micro-focus Industrial Computed Tomography (ICT) in situ, from which sequence CT images of the specimen under different loading levels were acquired. With application of Digital Volumetric Speckle Photography (DVSP), 3D displacement fields and strain fields in the specimen were calculated. The heterogeneous meso-structures in the concrete specimen can be seen as speckle patterns which are the deformation information carriers. From the displacement fields and strain fields analysis, deformation localization evolution and damage process are indicated, and the localization zone is consistent with the final position of failure in the specimen. Onset points of the micro-crack under CT resolution and the crack above CT resolution in the specimen are defined in the volumetric strain-axial stress curve, and the corresponding stresses of two points are 54.7% and 82.0% of peak loading, respectively. These two points also correspond to the onset points of dilatancy and plastic deformation, respectively. The results demonstrate that DVSP technique combined with CT can be applied to revealing the onset and development of deformation localization, and can be used for accurate measurement and visualization of 3D deformation.