Most concrete structures are biaxially loaded when cracking occurs and
propagates. A test equipment was developed to evaluate fracture mecha
nic parameters of concrete, based on the principle of wedge splitting.
Notched cubic specimens are tested under stable crack propagation. An
additional compressive load application device simulates a homogeneou
s biaxial state of stress. A force-crack opening displacement diagram
is obtained from which the specific fracture energy is calculated. The
strain softening behaviour is then evaluated by means of numerical mo
delling. The approach was applied for biaxially loaded concrete sample
s with 8, 16 and 32 mm maximum size aggregate (MSA). Based on the expe
rimental data a model is developed and discussed. It is found that the
fracture energy changes nonuniformly with increasing compressive stre
ss level, and that interaction of microcracking and aggregate interloc
king influences the fracture mechanism.