ABSTRACT
Abstract The leaching of calcium from dissolved portlandite crystals and C-S-H hydrates often contributes to the degradation of concrete structures. Since calcium leaching is a nonlinear phenomenon which is influenced by a wide range of parameters, the residual service life of the structures affected by this type of deterioration cannot be predicted satisfactorily on the basis of experimental results alone. In order to provide more fundamental information on this phenomenon, a numerical model was developed. The model considers the thermodynamic equilibrium between the pore solution and the various hydrated phases, and treats the deterioration mechanism from a macroscopic point of view. In order to validate the model, small disks of four different neat cement pastes were soaked for a 6-month period in a pH-controlled solution (pH 7). Test variables included the type of binder and the water/binder ratio. The initial transport properties of the various mixtures were determined by means of a tritiated water diffusion test, and the microstructural alterations of the paste samples were investigated by means of electron microprobe and TGA/DT A analyses. On the basis of the experimental results and the numerical simulations, various aspects of the leaching of calcium are discussed. Keywords: Calcium leaching, microstructure, durability, numerical modelling, service life prediction.
