Effect of Fatigue on Fracture Toughness of Concrete

An experimental study utilizing 4-point bending SENB specimens was carried out to determine the effect of fatigue on the fracture toughness of plain concrete. In addition to fourteen static tests of beams with a midspan precast notch, nine specimens with an initial precast notch of a depth to height ratio of l/d=0.20 were fatigued until a certain crack length was reached. Crack growth was successfully monitored by the CMOD compliance measurements. Independent surface crack length measurements by a hand-held scope and observations of the crack front with the use of a fluorescent dye-penetrant injected into the notch root were also performed. The fracture toughness, GIC, under fatigue appears to be higher than under static loading and shows an increasing trend with increasing crack length and number of loading cycles. The observed behavior is most likely related to the presence of a microcracking zone that evolves with fatigue.