Determination of fracture energy of ultra high strength concrete

In this paper, twenty-nine three-point bending beam specimens made of ultra high strength concrete (cube compressive strength of about 125 MPa and cylinder compressive strength of about 105 MPa) incorporating Ultra Fine Ground Granulated Blast-furnace Slag (UFGGBS) were tested. The depths of the beam specimens range from 75 mm to 300 mm. The fracture energy calculated by Hillerborg's work-of-fracture method, Bazant's size effect method, and Karihaloo-Nallathambi's effective crack method, as well as two empirical formulas of Bazant and Becq-Giraudon and of CEB-FIP Model Code 1990 were investigated and compared on the basis of the tested specimens. It was found that the results from the different methods were different from one another. In addition, the authors introduce a nonlinear regression method based on the effective elastic crack model to calculate the fracture energy. It is shown that the proposed method shows good tolerance on the scattered test data, and thus leads to a more consistent fracture energy value.