Determining initial fracture toughness of concrete for split-tension specimens based on the extreme theory

A theoretical method to determine the initial fracture toughness KIini of concrete for central-notched split-tension specimens was developed based on the extreme theory. In this method, the KIini, critical crack tip opening displacement CTODc, and half critical effective crack extension Δɑc could be obtained by the experimental peak load of a single specimen. The measurement of critical crack mouth opening displacement CMODc was unnecessary in this method. The fracture parameters were calculated using the cube and cylinder split-tension specimens. Results showed that the values of KIini obtained by the proposed method were slightly smaller than those obtained by the double-K method, and the difference between them generally decreases with the loading rates. And the values of CTODc and Δɑc obtained by the proposed method were more stable compared with those obtained by the double-K method.