Reconstructions by SPACE of the Interfacial Transition Zone

Of particular interest in concrete technology is the so-called Interfacial Transition Zone (ITZ). Conflicting experimental evidences as to the internal structure and extent of the ITZ, and even as to the very existence of it, make it attractive to confront such observations with a coherent picture of the ITZ produced by computer-simulation, although based on a simplified model concept. This contribution outlines the scientific framework for interpretation of the so-called packing phenomenon. A dynamic computer-simulation system, Software Package for the Assessment of Compositional Evolution, with the acronym SPACE was recently developed by the second author, and has been used for the present purpose. In addition to properly simulating composition of particulate materials, as can also be achieved by conventional systems based on random sequential procedures, it has been demonstrated earlier that SPACE can also more accurately reproduce configuration of particles in such materials. An hydration algorithm is additionally implemented in SPACE. Some preliminary information on gradient structures in the ITZ are discussed. The extent of packing gradients in the fresh and hardened state will be shown to vary with changes in material composition (water to cement ratio, cement fineness) and in the configuration-sensitivity of the parameter being studied. This implies structural gradients to extend further away from aggregate grain surfaces the more sensitive the very parameter is to packing configuration. Particular emphasis is given to this fundamental aspect, and not to properly estimating the ITZʹs thickness of this model cement paste near boundaries. Tools are provided to extract 2-D structural data from imaginary section planes (or from imaginary thin section projections) of the ITZ parallel to the interface. By making use of stereological methods, such data are given a 3-D structural meaning. Of course, direct information on porosity, packing characteristics and local particle distributions is available in 3-D. Therefore, in some cases direct 3-D measurements are possible, as well as visualisation of parts of the structure.