Acoustic Emission Source Localization Based Analysis of Crack Propagation in Steel Fiber Reinforced High- and Ultra-High Performance Concrete in Flexure

Definition, characterization and evolution of fracture process in concrete is still under discussion. This issue is particularly relevant for high- (HPC) and ultra-high performance concrete (UHPC), where steel fibers are added to ensure ductility and provide residual flexural strengths. As fibers add to the load bearing capacity by bridging cracks, more diffuse fracture develops, depending on the amount and type of fibers added. Understanding the development of this process contributes to a deeper insight into the mesoscale highly inhomogeneous fiber reinforced material. The primary fracture process at the crack tip, as well as fiber pull-out mechanisms, generate elastic waves that can be assessed using the acoustic emission (AE) analysis technique. Based on comprehensive low-cycle flexural tests using one HPC and one UHPC performed with AE detection, a post-processing approach for localization of AE events is outlined to define an “AE activity zone” representing the area of fracture process. In this paper, the standard deviation of the spatial dimensions of localized AE events is used to define such an activity zone. It is further shown, that the AE activity zone evolves differently depending on the compressive strength of concrete as well as the fiber content.