Atomistic Simulation of Cementitious Systems

The objective of the current thesis is to apply atomistic simulation techniques to further the current knowledge of cementitious systems. Hydrated cement is a part of concrete which is one of the most widely used materials in the world. As such the production of cement is responsible for about 5-8% of global CO2 emissions. The optimization of the mechanical properties and durability of concrete can therefore aid in the reduction of CO2 emissions. However hydrated cementitious materials are complex systems with many components: different hydrated phases, possibly unreacted cement grains of different composition and pore solution, possibly with organic additives. The aim of this thesis was to identify areas where classical atomistic simulation can be used to further our knowledge of cementitious systems. The focus was on the two main hydration products, portlandite and calcium-silicate-hydrate. For portlandite the atomistic mechanisms of growth from solution and the influences on the final morphology were studied. In addition to the interactions between the portlandite surfaces and water, the influence of different ionic species on portlandite growth has been considered. The influence of different ionic species present in the solution on the growth and final morphology of portlandite in cementitious systems has been observed previously. These phenomena are important to understand as portlandite growth influences the hydration kinetics of cementitious systems. Consequently a better understanding of the mechanisms governing the growth of portlandite might lead to a better control of the hydration kinetics. The final morphology of portlandite on the other hand will influence the final properties of cement, such as the mechanical strength or the diffusion of different ionic species in the cement microstructure. Our results indicate that water noticeably influences the relative interfacial energies and hence the equilibrium morphology of portlandite. Whereas the equilibrium morphology of portlandite in a weakly interacting environment is expected to be hexagonal platelets, in water the equilibrium morphology becomes equiaxed. Metropolis Monte Carlo calculations of the electrical double layer at the [00.1] portlandite surface indicate that the positive zeta potential measured experimentally in quasi pure portlandite-water systems may arise from the adsorption of C a2+ ions at what can be considered the outer Hemholtz plane, due to favorable interactions between the solvation shell of the calcium ions and the structured water region above the portlandite surface. The different origin of the charge at the interface leads to differences of the structural details of the diffuse