| Fracture and fatigue tests were carried out on many medium-strength concretes using notched cylinders to determine the effects of duration of curing on fracture properties. In this study, which is the first in-depth study of the above, it was found that changes in duration of curing affected different concrete mixes in dissimilar manners. Concrete with high fracture strengths lose fracture toughness, and decrease in size of fracture process zone with increasing curing time, while concrete with low fracture strength gain fracture strength and increase in size of fracture process zone with increasing curing duration. However, the effects of duration of curing at different testing ages were found to be varied, with significant changes in fracture toughness and brittleness. It is the first study to find strongly dissimilar trends in data obtained depending on the size of specimen being tested, and to point out that many previous published studies in fracture and fatigue of concrete carried out on single-sized specimens may have erroneous conclusions. The issue of structural size is shown to be critical in determining the comparative merits of different concretes, and it is shown conclusively that the current practices in obtaining the fracture properties of concretes are flawed because of the differences in the relative humidity histories in test specimens and in structures. |
