Size effect on fracture properties of concrete after sustained loading

To investigate the size effect on the fracture properties of concrete after sustained loading, concrete beams with three heights of 100 mm, 200 mm and 300 mm were first subjected to 30% peak load over 115 days. Thereafter, they were moved out from the loading frames and tested under standard static three-point bending (TPB) loading until failure. The initial fracture toughness, unstable fracture toughness, fracture energy and evolution of the fracture process zone were then derived based on the experimental results, and the size effect on these fracture properties of concrete after sustained loading were evaluated. The experimental results indicated that compared with the specimens under the static TPB tests without pre-sustained loading, the cracking initiation resistance for the concrete after sustained loading increased, resulting in the increase of the initial cracking load and initial fracture toughness. In particular, the tendency was more significant for the larger size specimens. By contrast, the effects of sustained loading on the unstable fracture toughness, fracture energy, critical crack length and FPZ evolution could be neglected. Furthermore, the size effects
on the fracture characteristics, including the fracture energy, and the FPZ evolution were obvious for the concrete specimens both under static loading and after sustained loading.