Numerical Analysis of Interface Fracture in Concrete Using a Lattice-Type Fracture Model

A key parameter in (numerical) models for simulating fracture of concrete at the meso-level is the behaviour of the interfacial transition zone between aggregate and matrix. In normal concrete the interface is a very porous thin layer with relatively low strength and stiffness. However, more dense interfaces can be obtained when different types of aggregates are used, or by means of selected additives to the cement matrix. Using a lattice-type fracture model of concrete, the effect of the interface properties on the global stress-strain behaviour is studied. To this end, splitting type tests on single particle specimens are conducted. Different types of aggregates are included. From the analyses, the sensitivity of the crack patterns to variations in interface strength and stiffness was obtained. Comparison with experimental observations is quite favourable. Next to the single particle specimens, concrete plates were tested, containing broken aggregates of the same material as used in the single particle plates. The effect of the type and size of the aggregates on the fracture geometry (fractal dimension) is analyzed. The results indicate that improved mechanical performance of composites may be obtained by carefully engineering the interface, taking care that an optimal ratio of weak to strong microstructural elements is present.