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Predicting leaching behaviour of cement based construction materials
This work describes the use of a reactive transport model to predict leaching of a large number of substances from solid porous cementitious products in a standardized tank leaching test. The model calculates molecular diffusion of dissolved ions and taking into account the effects of chemical reactions such as aqueous speciation, precipitation and adsorption that affect ion mobility by changing the distribution over solution and solid phase. The set of chemical equilibrium reactions that makes up the chemical equilibrium model, is derived from an independent pH-dependent leaching test on the same material, which also provides information on the reactive fraction of elements. To compose the reactive transport model the chemical model was combined with a 1 dimensional diffusion model. With this model that used the independently determined physical dimensions of the sample, its porosity, and density and the refresh scheme and volume of the external water solution as input. The only parameter that was fitted on the transport experiments is the tortuosity, which was derived from the leaching sodium. The model simulations show that the performance of the model critically depends on an adequate description of the chemistry of the material in combination with sufficiently detailed spatial discretisation of the cells used for the transport calculations, which needs to be detailed enough to represent the concentration fronts that develop during the test. Initially these fronts can be very sharp near the material surface. The small cells sizes limit the permissible length of the time steps, and therefore lead to relatively long calculation times. Although a mechanistic model prediction of a tank leaching test will be less accurate than a fitted empirical model, a mechanistic model is better able to predict leaching behaviour under environmental conditions.
Predicting leaching behaviour of cement based construction materials
This work describes the use of a reactive transport model to predict leaching of a large number of substances from solid porous cementitious products in a standardized tank leaching test. The model calculates molecular diffusion of dissolved ions and taking into account the effects of chemical reactions such as aqueous speciation, precipitation and adsorption that affect ion mobility by changing the distribution over solution and solid phase. The set of chemical equilibrium reactions that makes up the chemical equilibrium model, is derived from an independent pH-dependent leaching test on the same material, which also provides information on the reactive fraction of elements. To compose the reactive transport model the chemical model was combined with a 1 dimensional diffusion model. With this model that used the independently determined physical dimensions of the sample, its porosity, and density and the refresh scheme and volume of the external water solution as input. The only parameter that was fitted on the transport experiments is the tortuosity, which was derived from the leaching sodium. The model simulations show that the performance of the model critically depends on an adequate description of the chemistry of the material in combination with sufficiently detailed spatial discretisation of the cells used for the transport calculations, which needs to be detailed enough to represent the concentration fronts that develop during the test. Initially these fronts can be very sharp near the material surface. The small cells sizes limit the permissible length of the time steps, and therefore lead to relatively long calculation times. Although a mechanistic model prediction of a tank leaching test will be less accurate than a fitted empirical model, a mechanistic model is better able to predict leaching behaviour under environmental conditions.
Predicting leaching behaviour of cement based construction materials
Meeussen, Johannes C.L. (author) / Zomeren, Andre van (author) / Slott, Hans van der (author)
2006
10 Seiten, 1 Bild, 9 Quellen
Conference paper
Storage medium
English
theoretische Untersuchung , Tagungsbericht , mathematisches Modell , Diffusionskoeffizient , Ficksches Gesetz , Finite-Differenz-Methode , Flugasche , Zement , Theorie-Experiment-Vergleich , pH-Einfluss , Auslaugen (Mineralogie) , numerische Simulation , Konzentrationsverteilung , elektrische Leitfähigkeit , Gradient , Calcium , Silicium , Aluminium , Sulfat , Calciumaluminatsulfathydrat , feste Lösung , Cadmium , Zink , Kupfer , Molybdat , Phosphat , Arsenat , Chromat , Porosität , Feststoffdichte
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