Cracking in plain concrete: A multifield approach

Traditional phenomenological constitutive relationships sometimes fail in the description of mechanical behaviour of plain concrete. In such circumstances more refined models are necessary, which takes into account the multiphase structure of the material. This paper presents a generalised finite element formulation, which incorporates solid and fluid phases together with a temperature field. The model is developed to obtain time-dependent solutions of 2-D cases, such as concrete gravity dams subjected to loading-unloading cycles, non-homogeneous specimens subjected to thermo-mechanical effects, etc. A fully coupled cohesive-fracture discrete model, which includes thermal and hydraulic loads, is adopted to describe crack nucleation and propagation. The evolution of fractures leads to continuous topological changes of the domain and these are handled by systematic local remeshing of the domain and by a continuous change of fluid and thermal boundary conditions. In the adopted approach, cracks may nucleate everywhere depending only on the stress field and propagate along paths and with a velocity of the tip that is a priori unknown. The determination of the crack path and the velocity of the tip propagation represent an important part of the solution, as the temperature and stress fields and allows for correct updating of the domain. Governing equations are firstly presented together with their space discretization. The solution procedure is finally discussed in particular as far as the projection of the solution between two successive meshes is concerned.