Multiscale characterization and modeling of the viscoelasticity of the cement paste and the alike calcium-silicate-hydrate (C-S-H) at different levels of relative humidity

Authors: Chen, Zhao
Advisor: Sorelli, LucaSanahuja, Julien
Abstract: The phenomenon of creep has a long-term effect on the durability of the concrete structures. It has been widely agreed that concrete creep originates from the microstructure of calciumsilicate- hydrates (C-S-H). Being a formidable problem, the creep mechanism of C-S-H is still an enigma although numerous experimental and theoretical works have been done. Among the factors affecting the creep behavior of C-S-H, relative humidity (RH) is the primary one. The water content in the micropores plays an important role in the stiffness, the strength, and the viscosity of the microstructure C-S-H. The indentation technique allows characterizing the mechanical properties of the cement paste at the microscale and the nanoscale. Notably, the phenomenon of creep can be observed during the indentation holding phase. Compared with the traditional creep experiments lasting for months and years, indentation testing has the advantage of assessing the creep properties of the cement-based materials in minutes. In addition, it is easier for the specimen to reach the moisture equilibrium because of the small volume probed. To properly extract the creep properties, the first step is to establish the scheme of viscoelastic indentation. For this study, viscoelastic microindentation is analyzed by a spherical and a Berkovich indenter tip, respectively. The long term creep properties are well captured by the parameter of contact creep modulus (C) from logarithmic creep compliance. The mechanical properties of alike C-S-H structures of jennite and 1.4 nm tobermorite are then characterized by microindentation at various levels of RH. At the two levels of RH, the creep and the relaxation behavior of C-S-H is finally investigated by the statistical nanoindentation on a cement paste. The role of the water on the creep behavior of C-S-H is re-examined. The new findings for the creep mechanism of C-S-H are presented and discussed.
Document Type: Thèse de doctorat
Issue Date: 2019
Open Access Date: 29 November 2019
Grantor: Université Laval
Collection:Thèses et mémoires

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