Cover cracking of concrete slabs induced by rebar corrosion.

The phenomenon of concrete cracking due to corrosion of embedded reinforcement steel bars in concrete has been investigated for years. As a consequence of the steel corrosion that is accelerated by cold climates, sea water, spray and from chloride-based acceleration agents, internal cracks form. These agents originate a slow propagation of corrosion products around the embedded steel, forming a passive film, which can be elementary understood as a radial force present all around the steel, creating compressive stresses in concrete. This pressure causes the formation of microcracks that permit the passive film to infill in the structure and propagate. A finite element analysis will be carried out, in order to study the relationship of reinforced concrete features. These are the bar diameter, space between the rebars, concrete strength and the cover thickness. In order to simulate and describe the behaviour of the concrete, the Concrete Damaged Plasticity – CDP, is used. The elastic is easily described by the elastic modulus and the Poisson’s ratio, while the non-linear is more complex. The CDP method considers both compression and tension strengths, gaining as output the cracking pattern. The simulation proposed consists by the modelling of a two-dimensional model, in which the reinforced steel bars will be inserted as holes in the geometric features. The model features internal boundary conditions placed on each side of the rebars/holes. At the end, four groups of simulations are proposed, in which various combinations of the parameters considered, are provided. These corresponds of four different concrete strengths, three different diameters of the steel rebars, five different cover thicknesses and four different spacings between the rebars. The simulations show the probable cracking paths, based on the internal displacement given by the pressure formed by the corrosion products.