Moisture flow by micro structural contraction

Abstract

Material properties of building and construction elements are requested to last for an increasingly longer service life. For cementitious materials in particular, the "birth" of these properties emerge at the early stage of the hardening process. It is the development of the microstructure that determines the load bearing capacity as well as the quality in the material in the future. The quality of the microstructure realized at early ages with this affect the performance of a structures current and futures performance. As research areas focus more and more on micro-structural densification and durability related issues, deformational changes become increasingly decisive for a high quality guarantee. When considering the different research levels of concrete, the multi-scale modelling approach can be considered. When considering the paste captured in between two aggregate particles, the ribbon-model can be applied to simulate the hardening behaviour of this piece of paste. The article shows numerical simulations about the effect of capillary water expelled from the microstructure due to syneresis processes on the one hand and contraction of the microstructure due to hardening shrinkage on the other. Simulations of cement pastes, composed of different water/cement ratios, clearly demonstrate a movement of capillary water throughout the microstructures and its influencing on shrinkage. The simulation results show a slight influence of syneresis on water expulsion and on the deformation of the ribbon-paste.