Development of the strain field along the crack in ultra-high-performance fiber-reinforced concrete (UHPFRC) under bending by digital image correlation technique

The digital image correlation (DIC) technique was applied to the analysis of displacement fields along the surface cracks of ultra-high-performance fiber-reinforced concrete (UHPFRC) under a bending load. Analysis was performed on the fiber bridging forces acting on a unit area of cracked sections belonging to different regions (perfect bonding region, partial debonding region, and full debonding region), according to the fiber distribution characterization and DIC data. By using the DIC technique, the visualization and quantification of the UHPFRC fracture properties could be determined. The length of the uniform zone increased, whereas the fracture process decreased under the external load of the limit of proportionality (LOP). With the appearance of macro-cracks under the external load of the modulus of rupture (MOR), the length of the uniform and fracture process zones increased as the fiber content increased. However, the localization zone decreased. The steel fiber volume fractions had limited influence on the tensile strain at cracking and the complete debonding of fibers.