Effect of an accelerated chemical degradation on water permeability and pore structure of cementbased materials

In the field of the chemical degradation of cement-based materials, the models currently developed by the CEA are based on local chemical equilibrium and on diffusion as the main transport mechanism. Convective transport is not considered in the modelling approach. In this context, investigations were carried out in order to examine the evolution of water permeability with the degradation state. Accelerated leaching tests with ammonium nitrate were performed on CEM I (OPC) pure hardened paste and concrete. Water permeability was measured and pore structure analysed through MIP. The results showed that the accelerated ammonium nitrate leaching was governed by a diffusion process and was responsible not only for portlandite dissolution but also for CSH decalcification. This degradation generated a large capillary porosity (1–0·1 μm), and was responsible for a significant increase in total porosity. Water permeability for the paste (∼10⁻²⁰ to 10⁻¹⁸ m²) and concrete (∼10⁻²¹ to 10⁻¹⁹ m²) increased by about two orders of magnitude, and was well correlated with the porosity evolution. Dynamic elasticmodulus measurements confirmed the significant impact of this type of degradation on the final physicomechanicalstate of the materials.