Alizadeh, Rouhollah (Aali)2013-11-082013-11-0820092009Source: Dissertation Abstracts International, Volume: 71-06, Section: B, page: 3815.http://hdl.handle.net/10393/29910http://dx.doi.org/10.20381/ruor-13206The nanostructure, physical properties and mechanical performance of C-S-H, the principal component in cement-based materials, was studied. Synthetic C-S-H of variable composition was examined as a model system in comparison with that produced in the hydration of Portland cement. The current doctoral thesis is comprised of several research chapters designed to probe some of the ambiguous aspects of the C-S-H at the nano level. Several advanced analytical tools and novel approaches were utilized in order to elucidate various controversial issues in cement and concrete science. The studied topics include three areas of C-S-H investigation: nanostructural features, engineering properties and modified systems. Nanostructural Features -- The C-S-H (I) was categorized in two main classes separated at a C/S ratio of about 1.1. These exhibit distinct properties as determined by XRD, Helium Inflow, 29Si NMR and 43Ca NMR. New evidence was provided supporting the layered nature of the C-S-H. The role of interlayer water and calcium ions as well as silicate tetrahedra on physical properties of C-S-H analogs were evaluated. It was mainly demonstrated that the high C/S ratio C-S-H (I) can be considered as a viable model for the nanostructure of the C-S-H in hydrated cement paste. Engineering Properties - The relation between the chemistry and mechanical performance of the phase pure C-S-H systems was investigated. The dynamic mechanical response and stress relaxation of the synthetic C-S-H as well as C-S-H in hydrated Portland cement were examined at various moisture contents. A unique oscillatory response in the storage modulus and internal friction of the C-S-H materials was identified. Viscoelastic behavior of C-S-H was associated with the sliding of the C-S-H sheets. A mechanistic model as proposed to explain the observed changes in the mechanical properties of layered C-S-H materials. Modified Systems - Two approaches were evaluated in order prepare and characterize nanohybrid C-S-H phases: organic modification of C-S-H, and metamorphosis of C-S-H in cement paste. In situ polymerized C-S-H/polyaniline nanostructures demonstrated enhanced physical and mechanical properties attributable to the interaction of polymer molecules with the silicate structure of the inorganic host. C-S-H seeding was also employed in order to tailor the nature of the C-S-H product. It was shown that the chemical properties of C-S-H can be readily controlled depending on the stoichiometry of the seed. This offers a unique method in order to engineer the hydrated cement and concrete materials for improved sustainability.231 p.enEngineering, Civil.Thesis