Dynamics Of Water Confined In Cementitious Materials Studied By Neutron Scattering

Water is one of the most ubiquitous and important molecules on earth. Dynamics of water in various confinements can have a strong impact on the macroscopic properties of its confinements. Study of the water dynamics in confined geometries helps us to understand thoroughly the function and effect of the microscopic dynamics of confined water on the macroscopic properties of the system, thus modify and improve the properties of the confinement according to human’s need.Quasi-elastic Neutron Scattering(QENS) experiment is an excellent and novel technique for studying the water dynamics in confined system. With relatively high energy resolution, it can detect water dynamics on timescale from pico second to nano second. By analyzing the QENS spectra with appropriate theoretical models, one can obtain pertinent physical parameters regarding the dynamics of confined water, thus keep track of the dynamics of the confined water.In this work, the confinement systems under study are the ordinary Portland cement pastes and the new magnesium-oxide based green cement. Cement powder mixes with water and cure for some time, it will grow hard and produce microscopic pore system where water can exist. The dynamics and amount of this confined water changes with time and gradually and directly influence the structure of the pore system of the confinement, i.e. the cement pastes, and ultimately influence the macroscopic mechanical properties of the mature cement pastes, such as strength and durability.There are two main parts in this work. First, analyze the QENS spectra of the ordinary Portland cement pastes cured for different times and with or without additives, and obtain relevant physical parameters regarding the dynamics of confined water such as Bound Water Index, mean squared displacement, translational relaxation time, rotational relaxation time and self-diffusion constant. Second, analyze the QENS spectra of the magnesium-silicate-hydrate pastes under different temperatures and with and without additives, and obtain pertinent physical parameters on the dynamics of water such as structural water index, average relaxation time and rotational relaxation time.These physical parameters can quantitatively describe the dynamics of the confined water under various conditions, for example, the effect of curing time, additive, temperature and sample type on the hydration process and the dynamics of confined water, thus provide useful references for future design and research for enhanced and eco-friendly cement.