Influence of Different Microfibers on the Compressive Fatigue and Microcracking Behavior of High-Strength Concrete

The impact on microcracking and strain behavior of two different high-strength microfibers (steel and carbon) in compressive fatigue tests of high-strength concrete was assessed through systematic experimental investigations and microscopic analysis. To examine and compare the effects of the fibers on fatigue behavior and damage progression, the study involved determining the number of cycles to failure, axial strain, and a detailed microscopic evaluation of microcrack behavior. For this purpose, sections were taken from the specimens according to defined numbers of load cycles and thick sections were prepared. These thick sections were examined microscopically and evaluated regarding the amount, size and position of the microcracks. The number of load cycles to failure tended to be slightly lower for the fiber-reinforced specimens compared to the fiber-free specimens. The strains in the axial direction of the fiber-free specimens are lower until fracture. The microscopic analysis shows that microcracking primarily takes place in the interfacial transition zone (ITZ). The crack width changed only marginally during the applied load cycles and predominantly newly formed microcracks appeared with increasing degradation. This was found in both the fiber-free and fiber-reinforced specimens. The fiber-reinforced specimens show a reduced total crack area compared to the fiber-free specimens. Additionally, it can be concluded that the increasing degradation essentially is caused by the formation of new microcracks.