Dynamic Mechanical Response of Confined and Unconfined Concrete Reinforced with Recycled Steel Fibers

Concrete subjected to extreme loads, such as explosions that generate high strain rates, exhibits a significant increase in its mechanical properties. Concrete structures designed to withstand such mechanical loads are often made with concrete reinforced by randomly distributed short steel fibers, which enhance the material’s energy absorption capacity. A commonly used method to analyze the response of concrete to high strain rates is Split Hopkinson Pressure Bar (SHPB) technique. During the SHPB test, the transverse deformability of the specimen is not restricted, whereas in a real structure, it is confined by the surrounding material. In the SHPB test, inertial effects are believed to significantly influence the dynamic behavior of concrete. This paper examines whether inertial confinement affects the dynamic stress-strain relationship of fiber-reinforced self-compacting concrete (FR-SCC). Both confined (with a lead cover) and unconfined FR-SCC specimens were investigated under high strain rates ranging from 85 to 241 s⁻¹. The results of the SHPB experiments indicate that the confinement influenced the modulus of elasticity and the proceeding of the stress-strain curve in FR-SCC. However, the dynamic compressive strength was only slightly affected by confinement.