Influence of softening curves on the residual fracture toughness of post-fire normal-strength concrete

The residual fracture toughness of post-fire normal-strength concrete subjected up to $600^\circC$ is considered by the wedge splitting test. The initial fracture toughness $K_Iⁱⁿⁱ$ and the critical fracture toughness $K_I^un$ could be calculated experimentally. Their difference is donated as the cohesive fracture toughness $K_I^c$ which is caused by the distribution of cohesive stress on the fracture process zone. A comparative study on determining the residual fracture toughness associated with three bi-linear functions of the cohesive stress distribution, i.e. Peterson's softening curve, CEB-FIP Model 1990 softening curve and Xu's softening curve, using an analytical method is presented. It shows that different softening curves have no significant influence on the fracture toughness. Meanwhile, comparisons between the experimental and the analytical calculated critical fracture toughness values further prove the validation of the double-K fracture model to the post-fire concrete specimens.