Abstract Mortar is an important component of concrete. It is of great significance to obtain its tensile properties accurately. The structure heterogeneity of mortar specimens is high. Specimens are prone to fracture nearby interfaces between specimens and loading plates because of the inhomogenous stress distribution during the testing, which leads that effective tensile data can not be easily obtained. Therefore, through the improvement of specimen’s geometrical structure, the dumbbell specimen is designed for quasi-static direct tensile tests. Compared with the splitting test results, the quasi-static direct tensile testing of dumbbell specimens can be availably conducted to obtain the tensile strength. It also provides an effective approach to obtain the tensile parameters of mortar specimens. Moreover, numerical simulations on dumbbell specimens of mortar with different shapes are also conducted to explore the optimal geometrical structure in dynamic direct tensile tests.

Abstract Based on dynamic direct tensile tests, splitting tests and spalling tests, it is found that the experimental tensile strength of concrete-like materials greatly increases with loading-rate. This kind of dynamic tensile strength enhancement may be caused by the combination influence of the inertia effect, real rate effect and end friction effect (here the end friction effect is only existed in splitting and spalling tests). To further investigate the influence degree of real rate effect for concrete-like materials in dynamic tensile tests, this paper conducts systematically dynamic tensile experiments, viz. dynamic direct tensile tests, splitting tests and spalling tests. At the same time, numerical dynamic tensile tests are employed to analyze the mechanical characteristics of concrete-like materials. A hydrostatic pressure dependent model, the Drucker-Prager constitutive model, is used for concrete-like material specimens, which can consider the influence of inertia effect. In the numerical model, the specimen is set to be rate-independent, thus the predicted dynamic tensile strength of specimens is free of the real rate effect. The end friction effect is also taken into account in the numerical analysis of dynamic splitting and spalling tests. It is found that the dynamic tensile strength of concrete-like materials in numerical simulations does not varies obviously with the loading-rate, indicating that the inertia effect and end friction effect have little contributions to the dynamic tensile strength enhancement of concrete-like materials. Therefore, the real rate effect dominates the dynamic tensile strength enhancement of concrete-like materials in laboratory tests, but the inertia effect and end friction effect do not.

This paper presents the experimental results of recycled aggregate concrete (RAC) specimens prepared with five different amount of recycled coarse aggregate (RCA) [i.e. 0, 25%, 50%, 75% and 100%] subjected to compressive loading based on split Hopkinson pressure bar tests. Strain-rate effects on dynamic compressive strength and critical strain of recycled aggregate concrete were studied. Results show that impact properties of recycled aggregate concrete exhibit strong strain-rate dependency, and increase approximately linearly with strain-rate. The transition point from low strain-rate sensitivity to high sensitivity decreases with the increase of matrix strength.