Experimental Study On Compressive Fatigue Properties Of UHTCC

As the largest amount of used construction materials, concrete is widely used all over the world. The researches focusing on fatigue behavior of concrete show great importance for construction engineering, traffic engineering, and offshore engineering.Addition of fibre is an effective approach to improve the fatigue performance of concrete, which has been proved by many researchers. Ultra High Toughness Cementitious Composites (UHTCC) are fiber reinforced composites designed based on fracture mechanics concepts and micromechanical models. The composite exhibits significant strain hardening behavior and multiple cracking pattern. Most studies of the fatigue behavior of UHTCC focus on bending fatigue. To study the compression fatigue performance of UHTCC, a series of experiments with constant amplitude were designed, considering the influence of stress level and frequency.Based on the study of fatigue crack propagation and fibers damaged under fatigue load, the interface of fatigue failure specimens could be divided into three areas, including fatigue source area, transition area and quasi-static damage area. The fatigue source area existed the defects such as less fiber, so it crazed firstly. The fibers on the fatigue source area would be out of shape due to extrusion. On the other hand, fibers on quasi-static damage area, which formed in a very short time before the specimen occurring fatigue failure, tended to be pulled out and intact.Compression S-N curve of UHTCC was obtained from compression fatigue test under different stress level and the compression fatigue strength was0.688, which is higher than plain concrete and steel fiber reinforced concrete. With the decrease of loading frequency, the fatigue life of UHTCC was lower, which was indicated by compression fatigue test under stress level of0.85and with different frequency. In addition, the frequency influenced little on fatigue life within a certain range (0.5Hz to2Hz). The failure deformation of UHTCC under compression fatigue load was larger than that of corresponding static test with same stress level, which was much different from plain or steel fiber reinforced concrete.This research focuses on the analysis of deformation characteristic and failure process of UHTCC under compression fatigue load, which contributes to establishing compression fatigue model and potential application in engineering.