- Fracture of Concrete in Tension
The tensile strength of concrete is about 8-10 times lower than its compressive strength and tensile cracks are present in almost every reinforced concrete structure. Mode I fracture of concrete is therefore considered most important. For the ªctitious crack model the tensile stress-strain curve and the softening diagram are the essential input parameters. As mentioned in Section 2.4 direct tests are preferable, but due to several experimental difªculties are considered among the most difªcult to perform (see also Appendix 3 on test stability). In Section 6.1 we analyze the behavior of uniaxial tension tests, and explain the fracture process from 2D and 3D analyses. Next, we elucidate the effect of a number of experimental issues including the use of notches and the effect of the rotational freedom of the loading platens. Subsequently, in Section 6.2 two types of indirect tension tests are discussed, namely the Brazilian splitting test and the 3-point bending test. Although these experiments are easier to conduct, the softening parameters can only be determined via an inverse analysis, where the uniqueness of the parameters remains an issue.