Micro-mechanical performance study of the interfacial transition zone in ultra-high performance concrete containing coarse aggregates based on digital image correlation method

To measure the mechanical properties of the interfacial transition zone (ITZ) in ultra-high performance concrete with coarse aggregates (UHPC-CA) under direct load, a mesoscopic experimental analysis is performed using a combination of an electron microscope (EM) camera and digital image correlation (DIC) technology in this study. With such a methodology, the stress-strain curve of the ITZ under compression is measured directly. Furthermore, the distribution of the nominal compressive elastic modulus (E*) and Poisson's ratio (v) of the ITZ is obtained. Finally, the effects of granulated blast-furnace slag (GGBS) contents (0 %, 30 %, 40 %, and 50 %) on ITZ’s properties are investigated, and their relevance to microstructure is further explored by scanning electron microscope (SEM). The results indicate that the E * in the ITZ follows a 'U'-shaped distribution. In comparison to the reinforced matrix, a compaction process in ITZ is observed obviously, resulting in a smaller v in this region. Besides, as the GGBS content increases, the mesoscopic mechanical properties of the ITZ gradually decline.