Interfacial transition zone in concrete:
its relevance for engineering applications

P. Stroeven

Faculty of Civil Engineering and Geosciences, Delft University of Technology, the Netherlands

This paper discusses the characteristics of the interfacial transition zone (ITZ) relevant for engineering applications of concrete structures, in particular for permeability. Basis is the particulate nature at meso- and microlevel. The existence of the ITZ, its characteristics as to pore network development and to the resulting permeability are evaluated and illustrated by data obtained on DEM-based virtual cement paste. ITZ contributions to permeability are shown higher than from bulk. However, in research as well as under practical engineering conditions of the concrete, the material is not fully saturated as generally assumed and required for the derivation of permeability data from information on the pore network structure. The paper demonstrates that the relative prominence of the ITZ contributions to permeability are lost under such conditions. Hence, the general conclusion is that the ITZ is a real phenomenon, however gradient structures of various parameters will dramatically fluctuate on this low level of the particulate structure. For interpretation of this behaviour, the representative volume elements for structure-insensitive and -sensitive properties are introduced. Though, scientifically of interest, the actual engineering conditions lead to similar bulk and ITZ contributions to permeability.

Key words: Cement, concrete, discrete element modelling (DEM), interfacial transition zone, packing, permeability, representative volume element, pore saturation