Multi-scale characterization of concrete

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. 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.

Date of Award	2014
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology