Using the double-edge notched geometry proposed by Xu and Reinhardt recently, the
dimension of 200 mm×200 mm×100mm concrete cube specimens, of which the crack length are 10
mm, 20 mm, 30mm, 40mm, 50mm respectively, are designed to experimentally measure mode II
fracture toughness KIIC of concrete. For almost all specimens, typical shear fracture features i.e.
approximately 0º initial cracking angle as well the following crack forwards propagation along the
direction of ligament is phenomenally observed. This fact strongly confirms that this double-edge
notched geometry is validly and capable of being utilized as a mode II fracture geometry to evaluate
mode II fracture behavior. Then, from the discontinuity point of the measured load-displacement plot,
the critical shear fracture load Pc is determined and the corresponding mode II fracture toughness KIIC
is also calculated using the formula developed by Xu and Reinhardt. The computed results show that
KIIC has no dependency on initial crack length, about 3.36MPa·m1/2 for the tested specimens.