Experimental and phenomenological study of the effect of chemical detrimental processes on transport properties of concrete (PhD)

In recent years, SCK•CEN has acquired internationally recognised expertise in the modelling of  processes affecting the chemical and physical properties of concrete materials. The present proposal for PhD intends to further develop and to enlarge SCK•CEN's know-how in the domain of long-term behaviour of concrete materials by investigating the effects of chemical degradation processes on transport properties in concrete materials.

Interactions of porewater with cement will influence the long-term durability of concrete. In particular, chemical reactions will affect the physical properties, especially the total porosity or pore size distribution at the macro scale. Changes at the macroscale will affect transport properties (permeability and diffusion). In order to gain insight in processes influencing concrete degradation, water flow and solute transport behaviour during saturated/unsaturated and steady-state/transient flow conditions have to be known, both in undegraded and (chemically) degraded concrete. The proposed PhD research plans to investigate these aspects.

The objective of the PhD proposal is to investigate the effect of chemical degradation processes on transport properties in concrete at the  macro-scale, this is the homogeneous scale. To this end, the study plans to establish empirical/experimental relationships between:

• changes in porewater chemistry and/or the solid/mineralogical phase and the mechanical/physical properties such as total porosity and pore-size distribution, and
• changes in mechanical and physical properties on the one hand and changes in saturated unsaturated permeability, and diffusion coefficients on the other hand.

As part of the proposed PhD, simplified models describing these relationships will be developed and tested for macro-scale applications. The work programme includes experiments on  non-degraded and degraded concrete samples (a few centimeters thick). Chemical degradation tests will be set up to study the influence of carbonation and decalcification/leaching on transport parameters. This will be done by means of accelerated degradation methods (e.g. electromigration) as well as long-term experiments. Methods to characterise the permeability, diffusion and saturated/unsaturated flow conditions will be established.

Advanced (non-invasive) measurement techniques (X-ray tomography, NMR, and others) will be used to obtain quantative information on these processes. Transport experiments on undegraded and degraded cement/concrete will be performed using similar radio-tracer based migration techniques as developed by SCK-CEN on clay.

Transport properties will be estimated by inverse modelling techniques. Together with well-documented experiments taken from the literature, the relations between the different hydraulic and transport variables will be established.