Chemical reaction/transport modeling

Modelling release from a concrete mortar - The tank leach test data as obtained by NEN 7345 have been used to model the release of reactive components from a monolith making use of coupled chemical reaction and transport using ORCHESTRA. Over the duration of the test the leachant is renewed at regular intervals. The model output consists of the concentrations in the porewater within the product as a function of depth from the surface and the concentration build-up in the subsequent leaching cycles.

The model results for Na, pH, Pb and Mg are shown in comparison with the original measured data. It should be noted that the pH change with contact time has consequences for the Mg leachability, which is low at high pH. Thus after an initial increase of Mg a decrease of Mg is noted indicating reprecipitation taking place during a leaching cycle. From the porewater concentration profiles with depth the dissolution and precipitation reactions occuring at the interface can be onbserved

This type of modelling is expanded now by taking concrete - soil interaction into account, which add another level of complexity to the modelcalculations. Verifications against field observations are part of the ongoing research.