The microstructure development during bleeding of cement paste: an NMR study

NMR was applied to investigate the microstructure development of cement paste during bleeding. In this study, we have measured the void ratio and the T₁ relaxation, reflecting the pore structure development, at two fixed positions during the bleeding process of cement paste, whereas the void ratio was also measured over the complete sample during hydration. Here we have compared Portland and blast furnace slag cement and looked at various factors such as water-cement ratio, slag content and the use of water reducer. It was found that the void ratio at the top almost remains constant, and the void ratio at the bottom gradually decreased until it reached a constant value during bleeding. The results indicate that the finite-strain model is best suited to predict the structure development during a consolidation process. Moreover, it was found that the porosity is not totally linearly related to the distance as predicted by the consolidation model because of the existence of the transition zone.