Diffusion potentials in concrete - error and information source

Background

In porous materials such as concrete, the aqueous phase is likely to exhibit spatial differences in chemical composition, particularly in the cover zone, i.e. the zone of the concrete close to the exposed surface. Thus, profiles of sodium, potassium, hydroxide, chloride and other ionic species with increasing depth from the exposed surface are typically present. This leads to diffusion potentials in the cover zone of concrete.

Diffusion potentials may act as serious error source in electrochemical measurements, and thus negatively various non-destructive test methods used in condition assessment of concrete structures. On the other hand, diffusion potentials may also be used as source of information, i.e. with respect to the pore structure of the material or concerning the distribution of chemical species in the pore solution.

The present state of the art only allows a qualitative assessment of diffusion potentials, such as the sign of the diffusion potential arising under certain circumstances. The magnitude may be predicted given the main cause are differences in pH and the absence of perm-selective action (porous mortar or concrete). For other differences in pore solution chemistry (e.g. chloride profiles that are accompanied by multi-species concentration differences) or for denser concrete, prediction and interpretation of diffusion potentials is currently associated with large uncertainties – if not impossible. 

Aims and objectives

This project aims at improving the understanding of diffusion potentials in porous materials, particularly in concrete. On this basis, we aim at developing a predictive tool for diffusion potentials in concrete. This will have significant impact on a range of current research and engineering problems related to mass transport in concrete and reinforcing steel corrosion.