Research is focusing on increasing the strength and improving the durability of concrete for various reasons. The tensile strength and post-cracking behavior of ultra-high performance concrete (UHPC) in particular can be significantly increased by introducing steel fibres. However, the improvement in the mechanical properties of the concrete is always accompanied by a deterioration in the fresh concrete properties in terms of rheology and workability. This ultimately leads to the fact that the strength of steel fiber concretes and the post-cracking behavior can only be improved to a limited extent with the help of ordinary steel fibers, as otherwise a robust, quality-assuring workability is no longer guaranteed. To make this possible, shape memory alloys (SMA) are to be used as fiber reinforcement. These have the property of "remembering" a previously imprinted shape, which is possible due to a reversible, thermoelastic solid-state phase transformation from an austenitic high-temperature phase to a martensitic low-temperature phase. In this process, deformation back into the imprinted shape takes place either through thermal activation (one-way and two-way effect) or directly through stress relief (pseudoelasticity). This ability is to be used in such a way that fibers are added to the fresh concrete during the mixing process in a geometry that is positive for the rheology. While the concrete is still flowable, the fibers are "activated" by heat treatment. The resulting transformation into their molded form has a positive effect on the mechanical properties of the hardened concrete. The fibers made from shape memory alloys can therefore also be referred to as functional microfibers (FMF). When used in UHPC, the result is an FMF-UHPC.