Fracture mechanical behavior of concrete and the condition of its fracture surface

In this research project, a series of uniaxial, deformation controlled tensile tests were performed in order to study the fracture mechanical behavior of concrete. The parameters under investigation were the strength of concrete, curing conditions, concrete temperature and loading rate. The fracture surfaces of the tested specimens were investigated in detail and their condition was quantified using the fractal geometry. The evaluation of the experimental results and the results of the fractological investigation displayed correlations between the shape of the stress–crack opening relation of concrete and the values of the roughness as well as the fractal dimension of its fracture surface for all parameters under investigation. Relationships were drawn between the individual material as well as test parameters and the degree of concrete heterogeneity, which proved to be decisive for the formation and propagation of cracks in concrete. It was concluded that the roughness of the fracture surfaces might be considered as a representative replica of the crack system correlating directly with the concrete heterogeneity.