MIXED-MODE FRACTURE ENERGY OF CONCRETE

An interpretation of the very complex failure mechanism in four point shear specimens of concrete is proposed. A size-scale transition between tensile strength failure and mixed mode crack propagation is demonstrated to occur. When the distance of the central supports is large, the tensile strength is overcome at the supports by flexure. When the same distance is small, the tensile strength is overcome in the middle of the specimen by splitting. Pure shear failure does not seem to activate locally. As a matter of fact, the mixed mode fracture energy is substantially equal to the mode I fracture energy GF, each crack growth step being produced by a mode I (or opening) mechanism. © 1990.