The influence of testing conditions on damage zone of concrete in Uniaxial Compression: Insights from Stereo-DIC and computational modeling

• Uneven straining from bearings, jigs, etc., significantly affects concrete behavior. • Strain measurement of conventional devices depends on location & span of instrument. • Interaction of effects at loading boundaries can lead to miss-interpretation. • Specimen eccentricity alters how friction influences the collected response. • The strain measuring method adds to the inherent uncertainties of concrete behavior. With recent advances in non-contact optical measurement techniques, studying the response of concrete materials under specific mechanical loading conditions is evolving toward obtaining full deformation fields and mesoscopic mechanisms. Such data fields can be used to validate and improve theories and computational models of concrete-like materials. In this research, a commercial stereo DIC is used to acquire concrete’s deformation field in the Uniaxial Compression Test (UCT) to study the influence of loading conditions on the distribution of strains and the collected stress–strain responses. Specimens are grade C25 cylinders and prisms with an aspect ratio of 2 cast parallel to loading direction. Three conditions: ends’ constraint, low friction, and nonuniform straining are investigated experimentally and numerically. Obtained holistic data fields demonstrate the dependency of the outcomes on the location and length of conventional gauges. For instance, the snap-back mechanism can be related to the arrangement of measuring devices and local effects. Moreover, it is shown how nonuniform straining impacts the behavior of the material. Isolating different effects by numerical simulations showed how the interaction of effects (such as friction and seated block) leads to misleading observations. Besides computational modeling acquired data aid in understanding stress–strain relationship variations and conducting reliable tests.