Abstract:

In order to investigate the size effect of the fracture toughness of concrete, the size effect law deduced from Weibull＇s statistical theory was compared with that from Bazant＇s energy release principle, and three fracture parameters, namely, the initiatial fraction toughness （K1cⁱⁿⁱ）, the unstable toughness （K1cⁱⁿⁱ） and the critical crack tip opening displacement （δc） were tested. Moreover, 18 three-point bending specimens of notched beams were fabricated and divided into 6 groups according to their geometric similarity with the maximum dimension of 1280 mm in length, 320mm in height and 163 mm in width. The full-process curves of the load-crack mouth opening displace-ment and the load-displacement at loading points, as well as the strain in front of the cracks, were obtained by using the MTS tester and the dynamic strain tester. Calculated results indicate that the fracture toughness conside-ring the influence of process zone on the crack tip exhibits a certain size effect, and that, as compared with the size effect law suggested by Weibull, the one suggested by Bazant is more suitable for the prediction of the fracture toughness of large-sized concrete.

Key words: size effect, initiatial fracture toughness, unstable toughness, critical crack tip opening displacement