Dynamic Properties of Mortar in High-strength Concrete

Mortar is the matrix in concrete; at the meso-scale, concrete is a composite consisting of mortar matrix, coarse aggregate particles, and the interfacial transition zones between them. In this investigation, the mortars of three high-strength concretes were subjected to uniaxial compression and splitting tension at different speeds, from static to dynamic, to examine the effects of strain rate on their stress-strain and failure behaviour. Notable strain rate sensitivity was observed in both the compressive and tensile behaviour of the mortars, with the tensile response displaying greater rate dependence. The rate dependence for both tensile and compressive responses, varies little with mortar strength; i.e. similar rate sensitivity was noted for the three mortars studied. The dynamic increase factor (DIF) was adopted to evaluate strain rate dependence. Both the tensile and compressive DIF display a two-stage variation with strain rate, i.e. an initial gradual increase up to a transition strain rate, followed by a rapid rise thereafter; the transition occurs at similar to 1 s(-1) for tension, and similar to 30 s(-1) for compression. By fitting experimental data, empirical formulae were proposed for both the tensile and compressive DIFs of mortar. Finite element (FE) simulations of the static and dynamic tension/compression tests were also performed, using the JH-2 model to describe mortar. Good correlation between the simulations and experiments provides substantiation that strain rate dependence of the tensile/compressive strengths measured in dynamic tests are actual material properties.