Study of the relation between hydrated portland cement composition and leaching resistance

The present paper addresses cement compositions that have an optimal resistance against acid attack and hence, low leaching rates and optimal waste containment. To this end a shrinking core leaching model is used that describes the leaching of metals from a cement sample. This process is directly related to the calcium hydroxide removal from the sample by the acidified leachant. Effective diffusion coefficients in this so-called leached shell were calculated using the equations derived from a cement hydration model. This results in equations in which leaching rates were dependent on cement composition, especially the calcium hydroxide fraction. Optimizing the calcium hydroxide fraction yields cement compositions possessing the optimal leaching resistance as a function of the water porosity or as a function of the hydration degree and water to cement ratio used. The results were also used for the determination of optimal amounts of silica fume and fly ash. A comparison with experimental and practical data reported in literature yields good agreement.