Size-independent fracture energy of concrete at very early ages by inverse analysis

This paper deals with the analysis of fracture characteristics of concrete at very early ages. Experimentally, three-point bending tests are performed on concrete notched beams at very early age (before 24 h) to obtain the Load–Crack Mouth Opening Displacement (CMOD) curves. In order to find a trend of the fracture energy evolution, inverse analysis procedure is performed using finite element analysis. A damage softening model is used to describe the softening behaviour and a nonlinear inverse analysis algorithm (Levenberg–Marquardt) is adopted. As the softening damage model used does not take into account boundary effects, only a part of the Load-CMOD curves is fitted. Therefore, a good estimation of the size-independent fracture energy is obtained. The results obtained from the experimental test and the inverse analysis indicate an upward trend of the evolution of the fracture energy and other fracture concrete characteristics.