Numerical computation of the growth of microcracks in concrete during freezing cycles: Fid-Bau Portal

Numerical computation of the growth of microcracks in concrete during freezing cycles

Besson, F. / Huet, C.

A numerical computation tool has been developed in order to study the different mechanisms in the frost behaviour of concrete, in addition to experiments and theoretical study. A finite elements model in 2D is used to simulate the evolution of microcracking while taking account of the granular composite microstructure of concrete as a heterogeneous material with inclusions in a matrix. With this model, freezing in concrete and the crack propagation due to the increase of the volume of the ice is studied. The simulations are made with several circular inclusions into a matrix which contains several pre-existing microcracks. These inclusions represent aggregates, the matrix represents mortar. The porosity leads to an infiltration of water which swells owing to the increase of the volume of the ice. The microcracks propagate due to freezing and then cause scaling at the surface and internal damage in the sample. The first results obtained with this method are presented and are compared with previous ones. First, porous aggregates which swell in a cement paste lead to scaling at the top of the sample. Non-porous aggregates in a porous matrix which swell due to freezing lead to scaling and internal damage. Two time scales are considered: in the first one, freezing is uniform over the whole sample (slow air temperature change); in the second one, a frost front is simulated that progressively penetrates the sample and makes it freezing gradually (fast air temperature change). Cyclic frost front moves are also considered. The limitations and planned improvements of the model are discussed.