9. Testing of Concrete

Concrete is a heterogeneous composite material full of cracks, which play a vital role in its mechanical behavior and failure. A distinct characteristic of concrete is that it presents a softening behavior, as opposed to steels which present a hardening behavior. In concrete the crack-tip region is accompanied by a large fracture process zone in which microfailure mechanisms including matrix microcracking, debonding of cement-matrix interface, crack deviation and branching take place. All these mechanisms contribute to the energy of fracture. Concrete structures exhibit the so-called size effect according to which the failure load of a structure depends on its size. The size effect can only be explained with fracture mechanics concepts, while classical theories, such as elastic or plastic limit analysis cannot take into consideration this effect. In this chapter we briefly present the basic tests for the characterization of the mechanical behavior of concrete. They include compression, tension and bending tests. Furthermore, we present the basic principles of fracture mechanics applied to concrete, test methods for the determination of the critical strain energy release rate and an analysis of the size effect of concrete structures.