Numerical simulation of spall tests on concrete material with 3D meso-scale model

Abstract

Concrete is a common construction material used in both civil and defence engineering. In general, concrete exhibits much lower strength in tension compared to the compressive strength. Understanding the behaviour of concrete material in tension at high strain rate is essential in design and analysis of protective structures subjected to impact and blast loadings. Compared to direct tensile tests and Brazilian splitting tests, which are normally able to achieve strain rate up to about 1 1/s and 20 1/s, respectively, spall experiment is able to achieve higher strain rate up to the order of 102 1/s without the requirement of uniform stress in the specimen. Thus it has been more widely used recently in testing concrete materials for relatively higher strain rate range. However, concrete is a heterogeneous material with different components, but was usually assumed to be homogeneous, i.e. mortar material or so-called micro-concrete material with aggregates up to 2 mm, in most previous studies. It has been well acknowledged that neglecting coarse aggregates might not necessarily give accurate concrete dynamic material properties. In the present study, a 3D meso-scale model of concrete specimen with consideration of cement mortar and aggregates is developed to simulate spall tests and investigate the behaviour of concrete material under high strain rate. The mesh size sensitivity is examined by conducting mesh convergence tests.The reliability of the numerical model in simulating the spall tests is verified by comparing the numerical results with the experimental data from the literature. The influence of coarse aggregates on the measured signal is studied and suggestion is given. The wave attenuation in concrete specimen is analysed, and empirical equations are proposed for quick assessment of the test data. The contributions of aggregates to dynamic strength in spall tests are quantified for modifying the test results based on mortar material in the literature.