Mechanical degradation of ultra-high performance concrete under flexural fatigue loading

This work investigated the behavior of pre-cracked ultra-high performance concrete (UHPC) under flexural fatigue, quantifying its mechanical deterioration during cyclic loading through crack mouth opening displacement (CMOD), stiffness and energy dissipation rate. The flexural fatigue tests were carried at a frequency of 6 Hz on notched pre-cracked prisms in four distinct maximum load levels: 90%, 80%, 70% and 50% of the material residual bending strength at 0.5 mm of CMOD. The results presented expressive gain in fatigue life and performance for UHPC compared to a 50 MPa SFRC. In addition, a linear relationship between the residual bending strength and the initial stiffness was identified. Equations were proposed to predict the fatigue life according to the upper load limit during the cyclic loading. Finally, the post-fatigue behavior of samples that did not fail after 1,000,000 cycles was evaluated under monotonic bending test. No significant damage was observed on samples subjected to load levels below the endurance limit.