PORE-SIZE DISTRIBUTION IN BLENDED CEMENT PASTES USING NMR TECHNIQUES

Abstract

The microstructure of a porous system is an important characteristic of the material that largely determines not only its mechanical properties but also its transport properties and durability performance. In particular, for cement the porosity is strongly correlated with strength, and the permeability and the rate at which ions and gases diffuse through the material are of major importance for durability. In this work, Nuclear Magnetic Resonance (NMR) has been used in order to determine the pore size distribution in blended cements. The pore-size distribution was measured by the NMR cryoporometry method which is based on the well-known freezing point depression of water when confined inside the pore matrix of a material. It is demonstrated that this technique can be applied in cementitious materials,to probe the microstructure of the main hydration product: the cement gel. The influence of various mineral additives to the pore-structure and the transport of water have been assessed for a series of blended cements pastes. The pastes were left to cure at curing conditions of 20 +/- 2 degrees C for 28 days. In addition, the pore size distribution of the pastes was also determined by means of mercury porosimetry in order to compare the two methods used.