A nondestructive method for the determination of fracture energy in concrete structures

It is generally believed that linear elastic fracture mechanics concepts can not be employed in determining fracture parameters in concrete, and therefore most of the current research effort has focused on applying the principles in yielding fracture mechanics. Despite all these efforts, comparison of results reported by many investigators indicate wide variations in fracture toughness values even for essentially similar materials. The main source of discrepancy in the observed results is the existence of a large process zone at the crack tip. Hence, the amount of energy consumed in advancing the crack will depend on the size of the process zone, and in turn on the specimen size. Based on these considerations, the objective of this study is to develop a methodology for determining the fracture energy, Gf, for concretelike materials in a non-destructive manner. The method combines the principles of fracture mechanics and maturity (time-temperature effects) on fracture resistance development of concrete. The technique is based on a novel hypothesis in which the fracture parameters are related to the strength gain characteristics of concrete during the hydration process. The concept was examined with cube, cylinder and three different sizes of three-point-bend notched specimens. The range of tested specimens consisted of samples were cured under three different isothermal temperatures (14°C, 23°C and 35°Q. The specimens were tested at six ages from 0.25 to 45 days. The hypothesis is verified through inverse determination of thermodynamic characteristics of concrete for the specimen tested. Based on the theoretical basis and statistical analysis of about three hundred tests, the results show that the activation energies obtained from the three-point bend test and from compressive tests are similar. And results also illustrate that the maturity method may be used to predict the in-place fracture energy of concrete structure based on its thermal history