Ulrike Karr, Reinhard Schuller, Michael Fitzka, Andreas Denk, Alfred Strauss, Herwig Mayer
April 29, 2017
The ultrasonic fatigue testing method has been further developed to perform cyclic compression tests with concrete. Cylindrical specimens vibrate in resonance at a frequency of approximately 20 kHz with superimposed compressive static loads. The high testing frequency allows time-saving investigations in the very high cycle fatigue regime. Fatigue tests were carried out on “Concrete 1” (compressive strength f c = 80 MPa) and “Concrete 2” (f c = 107 MPa) under purely compressive loading conditions. Experiments at maximum compressive stresses of 0.44 f c (Concrete 1) and 0.38 f c (Concrete 2) delivered specimen failures above 10 9 cycles, indicating that no fatigue limit exists for concrete below one billion load cycles. Resonance frequency, power required to resonate the specimen and second order harmonics of the vibration are used to monitor fatigue damage in situ. Specimens were scanned by X-ray computed tomography prior to and after testing. Fatigue cracks were produced by ultrasonic cycling in the very high cycle fatigue regime at interfaces of grains as well as in cement. The possibilities as well as limitations of ultrasonic fatigue testing of concrete are discussed.