Fracture characteristics of concrete at early ages

The purpose of this study is to experimentally investigate, at early ages, the fracture characteristics of concrete such as critical crack tip opening displacement, critical stress intensity factor, fracture energy, and bilinear softening curve based on the concepts of the effective-elastic crack model and the cohesive crack model.A wedge-splitting test for Mode I was performed on cubical specimens with an initial notch at the edge. By taking various strengths and ages, load-crack mouth opening displacement (CMOD) curves were obtained and these curves were evaluated by linear elastic fracture mechanics and finite element analysis.The results from the test and analysis indicate that critical crack tip opening displacement decreases and critical stress intensity factor and fracture energy increase with concrete ages from Day 1 to Day 28. By numerical analysis, four parameters of bilinear softening curves from Day 1 to Day 28 were obtained. In addition, it was observed that the parameters f_t and f₁ increase and the parameters w₁ and w_c decrease with increasing age. The obtained fracture parameters and bilinear softening curves at early ages may be used as a fracture criterion and an input data for finite element analysis of concrete at early ages.