Degree Type

Dissertation

Date of Award

2018

Degree Name

Doctor of Philosophy

Department

Civil, Construction, and Environmental Engineering

Major

Civil Engineering

First Advisor

Behrouz Shafei

Abstract

Despite the significant amount of concrete produced worldwide, there are long-standing issues with the long-term performance of concrete structures and facilities subjected to the mechanical and environmental stressors. To settle these issues, it is first imperative to understand the structural hierarchies and heterogeneous characteristics of concrete. While the structure of concrete at large length scales have been widely investigated in the literature, little knowledge is available about the structure, composition, and properties of the smallest building blocks of concrete, i.e., hydrated cement paste (HCP). This is mainly due to the complexities involved in the atomic structure of HCP phases that are often difficult to be characterized using conventional experimental methods. Atomistic simulations, however, can offer a promising solution, which not only plays a critical role to further interpret the experimental test results, but also advances the fundamental knowledge that is not accessible otherwise.

In this dissertation, a robust bottom-up computational framework supported with experimental test data is established to address three categories of research needs. These research needs seamlessly connect the atomic structure of cement-based systems to the long-term performance of concrete structures at the macroscale. The first category of research needs attempts to understand the interplay between the structure and properties of the crystalline HCP phases, including portlandite, and the AFt and AFm phases. The second category of research needs deals with the characterization of the magnitude, sign, and directionality of the mechanical stresses produced as a result of the formation of the secondary sulfate-bearing minerals during the chemical sulfate attack reactions. Lastly, the third category of research needs is associated with the identification of the atomistic processes underlying the diffusion of water molecules and chloride ions at the interfaces of the main aluminum-rich phases in HCP.

The outcome of this study (1) will extend the fundamental knowledge about the structure, dynamics, and properties of the HCP phases at the nanoscale, (2) will offer an invaluable addition to the existing experimental test data, and (3) can directly contribute to understanding and controlling the long-standing issues due to the deterioration of concrete structures subjected to the mechanical and environmental stressors.

Copyright Owner

Shahin Hajilar

Language

en

File Format

application/pdf

File Size

237 pages

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