ITZ's structural evolution during hydration in model concrete

The interfacial zone (ITZ) around aggregate in concrete is a crucial element in mechanical and in transport systems. Computer simulation of cement is used to approach this phenomenon. For particle-packing in the fresh state, the Software Package for the Assessment of Compositional Evolution (SPACE) system relies on a dynamic generation algorithm, reflecting production conditions. The evident effects of spatial position of hydrating particles and hydration products on structure formation of cement call for use of stereological methods. Morphological and structural evolution of the ITZ from the fresh into the hardened state is quantified by composite as well as configuration parameters. The results reveal that in the fresh state of particle packing, the 'wall effect' reflects the decline in cement particle density in the vicinity of the aggregates, leading to a more porous ITZ, the extent of which depends on technological parameters (water-to-cement (w/c) ratio, cement fineness), but also on the type of parameters characterising material structure. As hydration proceeds, only moderately higher porosities are observed within the ITZ than in the bulk paste. The disproportional high physical bond strength in the ITZ at low w/c ratio remains apparent throughout the hydration process.