Fatigue behavior and effect of stimulated autogenous self-healing in Ultra High-Performance Concrete

This paper investigates the mechanical response under fatigue cycles in Ultra-High-Performance Con-crete (UHPC) under four-point flexural loading, focusing on the effect of damage recovery triggered by stimulated autogenous self-healing. Thin beam specimens were pre-cracked up to 0.25 mm residual crack opening displacement under monotonic loading and then subjected to cyclic loading with a fre-quency of 5.5 Hz and a load amplitude equal to 10-80% of the load corresponding to the load at residual pre-crack width. Cyclic loading was applied for 700,000 cycles or up to the attainment of 1 mm total crack opening displacement at maximum load, whichever was reached first. Specimens were then healed underwater, and the fatigue tests were repeated to failure after the scheduled healing period of 1, 3, or 6 months. Self-healing performance was assessed via ultrasonic pulse velocity test and micro-scopic image analysis. Furthermore, the effects of self-healing in fatigue-crack growth rate, stiffness degradation, and critical crack opening were identified together with the benefits brought in as residual fatigue life recovery. The three-month healed specimens showed up to twenty times reduction in the rate of crack opening displacement as compared to the same specimen before the healing period.