Effect of tensile cracking on diffusivity of mortar: 3D numerical modelling

Durability of concrete structures can be severely affected by the presence of cracks, whatever is the cause of these cracks: early-age, thermal loading, shrinkage, or a simple mechanical overloading. The paper gives a method and a 3D numerical tool to estimate and predict in a short time the influence of tensile cracks on HTO diffusivity of mortar. Firstly, the methodology adopted to model the mechanical behavior of mortar under 1D tensile loading and its diffusivity at different strains taking into account the 3D description of the material is presented. Then the methodology is applied and validated on a specific mortar that has been previously studied experimentally in the literature. The hydration model CEMHYD3D is used to generate a 3D numerical microstructure of w/c = 0.4 portland cement paste and a mesostructure of mortar. The voxelized images are then transferred from CEMHYD3D to a finite element code in order to simulate 1D tensile behavior of the mortar and its diffusivity before and after the mechanical loading. The outcomes of the FE simulation at the microscale (cement paste) is used as input data at the mesoscale (mortar) modelling. HTO concentration distribution in the whole cracked mesostructure according to the three directions is obtained. Cracks appear as preferential pathways for the penetration of HTO. Diffusion coefficients in the steady state are calculated for uncracked and cracked mortars. The increase rate of diffusivity for a cube of mortar with 6.25 mm per side is quantified for different strain values corresponding to different crack states. An increase by a factor of 1-8.4 times is found. The modelling results are then successfully validated by comparison to experimental data.