Influence of compaction on the interfacial transition zone and the permeability of concrete

The interfacial transition zone (ITZ) is regarded as a key feature for the transport properties and the durability of concrete. In this study one self-compacting concrete (SCC) mixture and two conventionally vibrated concrete (CVC) mixtures are studied in order to determine the influence of compaction on the porosity of the ITZ. Additionally oxygen permeability and water conductivity were measured in vertical and horizontal direction. The quantitative analysis of images made with an optical microscope and an environmental scanning electron microscope shows a significantly increased porosity and width of the ITZ in CVC compared to SCC. At the same time oxygen permeability and water conductivity of CVC are increased in comparison to SCC. Moreover, considerable differences in the porosity of the lower, lateral and upper ITZ are observed in both types of concrete. The anisotropic distribution of pores in the ITZ does not necessarily cause anisotropy in oxygen permeability and water conductivity though.