Abstract
In this recommendation, standard testing methods for determination of the double-K criterion for Mode I crack propagation in concrete using wedge-splitting tests and three-point bending beam tests are specified for the fracture parameters of the initial cracking toughness K_{Ic}^{ini} and the unstable fracture toughness K_{Ic}^{un}. Along with the recommendation of the standard testing methods, the theoretical background of the double-K criterion, the calculation methods and the results of round-robin testing for determining the double-K fracture parameters are presented in technical reports [1, 2]. The recommendation of the standard testing methods includes geometry for specimens, fabrication of specimens, testing machine, load transmission system and supports, measuring instruments, determination of initial cracking load Pini, determination of measured maximum load Pmax and initial compliance ci, calculation methods for wedge-splitting test and three-point bending beam test, as well as the testing results and testing report forms. According to these methods, the measured fracture parameters of double-K criterion can be used to describe the onset of cracking, and the onset of unstable cracking or failure for predicting crack initiation, structure failure and crack stability in concrete structures.
Highlights
In this recommendation, standard testing methods for determination of the double-K criterion for Mode I crack propagation in concrete using wedgesplitting tests and three-point bending beam tests are specified for the fracture parameters of the initial cracking toughness KIicni and the unstable fracture toughness KIucn
Two methods are specified in this recommendation for the determination of the initial cracking toughness KIicni and the unstable fracture toughness KIucn by means of wedge-splitting tests and three-point bending beam tests. Note that these methods are specially recommended for mortar and concrete
Testing methods are recommended for the determination of double-K criterion
Summary
The geometries for wedge-splitting specimen and three-point bending beam are illustrated in Figs. 1 and 2 respectively. Consider the following items to get appropriate size of specimen. 1. The size of specimen depends on the maximum size of aggregate dmax. Dmax can be determined by sieve analysis. D =specimen depth, W =specimen width, B =specimen thickness, f = groove depth, e=groove width, a0 = initial notch depth. 3. Since larger the specimen is, greater stiffness the test machine should provide, size of the specimen should be limited for less-equipped laboratories to perform tests. 4. The ligament of the specimen is recommended to be larger than 5 times the maximum aggregate size dmax
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