Cyclic tensile behavior of high strain hardening UHPC analyzed by acoustic emission techniques

Understanding the cyclic tensile behavior of high strain hardening ultra high performance concrete (UHPC) is important in structural design and for predicting its damage state. In this study, acoustic emission (AE) analysis was applied to monitor the damage evolution process of high strain hardening UHPC under direct tensile cyclic loading at different objective tensile strain levels. The test results show that when the objective strain is in the elastic state, the tensile cyclic stress-strain curves show marginal change, whereas when it is in the strain hardening state, the residual strain and the stiffness of UHPC are reduced by increasing the number of cycles and finally tends toward stability, the maximum stress remains stable. The AE analysis results can help to explain the evolution of the mechanical properties of high strain hardening UHPC under cyclic tensile loading and proves the existence of the Kaiser effect, which can be used to quantify the deformation and the degree of damage of UHPC. The stiffness of UHPC under cyclic tension is controlled by the nominal debonding length of the steel fibers. Finally, the relationship between the total tensile strain and the loading stiffness degradation ratio under cyclic tension was proposed and could be employed in evaluate of stiffness of the high strain hardening UHPC under cyclic tension in some extent. (C) 2020 Elsevier Ltd. All rights reserved.