Abstract
This thesis describes a series of 1H nuclear magnetic resonance (NMR) experiments to investigate connectivity of the the nanopores of the calcium-silicate-hydrates (C–S–H) in cement based materials. This is achieved by coupling 1H NMR relaxometry in one and two relaxation times dimensions and 1H NMR cryoporometry down to about -80C. In particular the thesis contains the first use in any system of coupled two dimensional relaxometry and low temperature cryoporometry. The cryoporometry has been validated on model porous silica glass (SiO2) materials with known pore sizes and then applied to C2S and C3S, in cement chemistry notation, otherwise known as alite and belite. The 1H NMR cryoporometry data was used to estimate the pore sizes in C2S. It was found that the T2 relaxation time depends on temperature in C2S and C3S, but not in porous glasses SIO2 and MCM-41. There are two possible explanations. It could be due to the interaction of water with the -OH groups on the pore surface. It is known, that water, or a monolayer of water becomes physisorbed on silanol groups. Silanol groups are present both at the silica glasses surfaces as well at the cement pores surfaces. However, there are no many studies available on the interaction of water-silanol groups and temperature dependency below 0C. The other explanation concerns hydrated calcium ions in cementitious materials not present in silica glasses. However, little is known about C–S–H surfaces. A two dimensional 1H NMR T2 − T2 exchange experiment was used to investigate the exchange of water between interlayer spaces, gel pores and capillary pores at temperatures of room temperature, -5C and -30C on cooling and again on warming in C3S. A 3- site exchange numerical model was written to solve the associated coupled differential magnetisation exchange equations. By comparing the model output and experimental data it was shown that water exchanges between interlayer spaces and gel pores and between interlayer spaces and capillary pores. However, there is no exchange from gel pores to capillary pores. A further set of room temperature experiments were carried out to investigate the change in the pore size distribution of C-S-H in white cement following desorption and resorption of water as a function of drying severity. Rearrangements of the nano porosity were seen dependant on the severity of the drying. There were both reversible and irreversible changes. However, the total pore volume remained constant within measurement error. Most interestingly for more severe drying relaxation of the pore size distribution was seen for several days following resorption of water. All the experimental work was carried out at the LafargeHolcim research laboratories in Lyon, France. The thesis also contains details of the adaptation necessary to carry out experiments described on a standard Maran Ultra 23.5 MHz NMR spectrometer.