THESIS
2014
iii, iv-xxi, 239 pages : illustrations (some color) ; 30 cm
Abstract
In this study, cement-based materials have been investigated by multiple techniques,
including scanning electron microscopy (SEM) coupled with backscattered electron (BSE)
and energy-dispersive X-ray spectroscopy (EDX), thermo-gravimetric analysis (TGA), X-ray
diffraction (XRD), nanoindentation technique and macroscopic mechanical tests.
Through this investigation, the mechanical parameters (elastic modulus and hardness) of
different phases (like outer product, inner product, calcium hydroxide, remained fly ash
particles, remained slag particles, and residual cement grains) in cement-based materials
have been characterized and analyzed. Calcium-silicate-hydrate (C-S-H) gel, the main product
of cement hydration, contributes the most to the engineering properties of concrete. Henc...[
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In this study, cement-based materials have been investigated by multiple techniques,
including scanning electron microscopy (SEM) coupled with backscattered electron (BSE)
and energy-dispersive X-ray spectroscopy (EDX), thermo-gravimetric analysis (TGA), X-ray
diffraction (XRD), nanoindentation technique and macroscopic mechanical tests.
Through this investigation, the mechanical parameters (elastic modulus and hardness) of
different phases (like outer product, inner product, calcium hydroxide, remained fly ash
particles, remained slag particles, and residual cement grains) in cement-based materials
have been characterized and analyzed. Calcium-silicate-hydrate (C-S-H) gel, the main product
of cement hydration, contributes the most to the engineering properties of concrete. Hence,
the microstructural mechanical and physical properties of C-S-H gel in cement-based
materials have been studied by the coupled nanoindentation and SEM-BSE/EDX analysis
in detail. The physical and mechanical properties of C-S-H gel were linked through the
micro-poromechanical approach. Insights into the microstructural features of C-S-H gel helped
to improve current understanding of its nature. Additionally, this study examined the differences
among the C-S-H phases formed in the different cementitious composites and revealed the
influence of mineral admixtures (silica fume and fly ash) on the properties of the C-S-H phase. The nanoindentation/SEM technique was then extended to study the mechanical and
physical properties of natural aggregate, interface transition zone and cement paste matrix
in mortars.
Subsequently, based on the experimentally obtained phase properties, a homogenization
method was adopted to characterize the elastic constants of hydrating cement paste, mortars
and concrete at different scales. Finally, the predicted elastic moduli were compared the
experimental data, and it was found that the proposed method could provide a very accurate
prediction of the elastic modulus evolution of hydrated cement paste.
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