FRACTURE TOUGHNESS AND MICROSTRUCTURE OF CONCRETE AT EARLY-AGES

This paper reports the results of a study on fracture behavior of concrete at early ages. The two-parameter fracture model has been used to determine the fracture toughness K-Ic(s) and critical crack tip opening displacement (CTODc). Meanwhile, microstructure parameters such as pore size distribution have been studied by mercury intrusion porosimetry (MIP). The parameters were obtained for three types of concretes at different ages from 18 hours to 28 days. It was found that K-Ic(s) increases with hydration time, but porosity changes in the opposite way. The lower water-cement ratio led to a more rapid development of K-Ic(s) at early ages. There existed a close relationship between K-Ic(s) and porosity. In addition, the interfaces between coarse aggregate and cement matrix were studied by scanning electron microscopy (SEM) at the age of 28 days to interpret its influence to mechanical properties.