Mechanical properties measurement and micro-damage characterization of ITZ in concrete by SEM-DIC method

Due to the limitation of current experimental measurements, there is an almost insurmountable challenge to determine the mechanical tensile properties of interfacial transition zone (ITZ) in concrete. The present work aims to experimentally characterize micro-mechanical properties of ITZ under tensile load with the combined strategy of scanning electron microscope (SEM), digital image correlation (DIC), nanoindentation and wavelet packet technology. A bi-material sample composed of aggregate and mortar in the same volume and shape is designed for convenience to conduct tensile experiments using the proposed SEM-DIC method. By analyzing the stress obtained from the loading device and full-field strain calculated through DIC technique, the mechanical properties including tensile strength, nominal fracture energy (GNF) and nominal tensile elastic modulus (ENT) of ITZ are evaluated. Nanoindentation tests are also conducted, and their results are briefly compared with that of SEM-DIC method. The micro-damage distribution in ITZ area is further evaluated by wavelet packet analysis. Results reveals that a region with apparently lower ENT values can be characterized as the ITZ area, in which the average ENT value is about 55% of that of the mortar. In addition, growing path of microcracks can be estimated by the direction of maximum principal strain, and the degree of micro-damage could be well characterized by energy change rate (ECR) through wavelet packet analysis.