Reactive transport in porous mineral systems - experiments and numerical analytics

 
Cement-based materials are exposed to massive degenerative influences from water-soluble pollutants. In order to protect these materials, they are functionalized by providing the inner surfaces with new additional properties. The high reactivity and the porous structure of the cement-bound material are used for this purpose. This is achieved by using organosilicon compounds applied to these porous materials in order to reduce the capillary absorption of aggressive aqueous solutions through a water-repellent effect. The silanes also penetrate into the material through the capillary forces, react in the pores with the water present there and finally form a water-repellent / hydrophobic film on the inner pore walls, which reliably prevents the penetration of further in water dissolved pollutants. This functionalization is based on a reactive transport process, i.e. transport processes and chemical reactions take place simultaneously and influence each other. In order to consider environmental influences and to improve the performance of such a functionalization, basic knowledge of the highly complex mechanisms related with it is required. So far, mainly experimental investigations have been carried out on the reaction mechanisms of organosilicon compounds in the pore solution and their interaction with the solid matrix. However, the results are not sufficient to adequately understand and optimize the processes during impregnation with organosilicon compounds. Suitable methods for further investigations of reactive transport are based on numerical models. This paper presents such a model for the description of the reactive transport of organosilicon compounds in cement-based materials. With the help of data from mercury intrusion porosimetry and the software package "PoreXpert" it is possible to create a pseudo-realistic 3-D pore model for different porous materials such as concrete. Then the transport equations and the equations describing the chemical kinetics are linked with the SOFTWARE package COMSOL-MultiPhysics and implemented into the 3D pore model. It can be shown that the influence of the material properties of organosilicon compounds on the transport behavior is realistically represented by the model. In the future, the results of calculations on structure-activity relationships in combination with simulations on reactive transport will be used as a basis for molecular modelling and development of new silane types.