Dynamic Strength Enhancement of Conventional Concrete

In order to investigate the performance of conventional concrete at different loading rates, experimental results of strength enhancement were obtained under tension and compression tested under different loading speeds. G-mix specimens prepared at the Tyndall Air Force Base were used to determine the range of loading rates of the servo-hydraulic equipment at hand and to obtain experimental results with a series of indirect tension and uniaxial compression tests. For interpretation of the experimental observations, a comprehensive triaxial concrete model was extended from rate independent elasto-plasticity to rate dependent visco-plasticity using the Duvaut-Lions overstress formulation. The visco-plastic concrete model was adopted to explore the dynamic strength enhancement in tension, compression and shear in terms of a single viscosity or rather relaxation time. In concrete the failure properties, i.e., the triaxial strength and the failure mode, depend not only on the load path, but also on the loading rate especially at high speed impact. In this paper an effort was undertaken to assess the diffuse and localized failure modes of the triaxial concrete model and its visco-plastic extension.