Fracture behavior of ultra‐high performance lightweight concrete: In situ investigations using μ‐CT

In various research projects at the University of Kassel, the concept of lightweight concrete has been combined with that of ultra‐high performance concrete (UHPC). Due to the high performance of the UHPC matrix, lightweight concretes (UHPLC) with strengths of 60‐130 MPa and bulk density of 1.5‐1.9 kg/m³ were developed. This material can be used in many applications because of its low thermal conductivity, low weight and thus easy to transport, recyclable and can be prefabricated. Thus, it meets today's multifunctional requirements for building materials. The brittle material failure of UHPC without fibers is not observed with UHPLC. Instead, the concretes fail in hourglass shape under compressive stress, as seen in standard concretes. This constellation is not only responsible for the reduction of strength and Y‐modulus, but also predicts a ductile failure. For a better interpretation of the fracture behavior and fracture pattern, images of the UHPLC were taken in a highresolution computed tomography (μ‐CT) scanner. Between images, the sample was loaded and the load was kept constant during the measurement. The data was evaluated on the basis of a damage parameter, as well as crack openings during stable crack growth and the crack pattern after the maximum load was exceeded.