Date on Master's Thesis/Doctoral Dissertation

5-2024

Document Type

Master's Thesis

Degree Name

M.S.

Department

Civil and Environmental Engineering

Degree Program

Civil Engineering, MS

Committee Chair

Kim, Young Hoon

Committee Co-Chair (if applicable)

Sun, Zhihui

Committee Member

Sun, Zhihui

Committee Member

Sathsuksanoh, Noppadon

Author's Keywords

Geopolymer; microstructure; CaO; water content; curing temperature

Abstract

Geopolymer, an emerging alternative to Portland cement-based concrete, relies on alumina and silica-rich precursors like fly ash for its formation. Geopolymerization is a chemical process that creates a three-dimensional polymer network by reacting with an alkaline activator. While fly ash's calcium oxide (CaO) content is crucial in its classification, it behaves differently in geopolymerization, where it competes with hydration. Therefore, a better understanding of the impact of CaO content in fly ash on geopolymerization is needed to effectively utilize fly ash. This study investigates the effects of CaO content, water, and curing temperature on geopolymerization. Using fly ash from a local power plant in Kentucky and alkali solutions, various parameters are tested, focusing on formation, microstructure, and mechanical properties of geopolymers. Compressive strength, X-Ray diffraction analysis (XRD), Fourier transform infrared (FTIR), and scanning electron microscope (SEM) analyses were employed to assess the as-received fly ash and modified fly ash by adding CaO. Compressive strength tests reveal that 0.4 water-to-binder ratios and 75 °C (167 °F) curing temperatures accelerate polymerization, enhancing strength. However, CaO addition diminishes strength due to incomplete formation of Calcium silicate hydrate (C-S-H). SEM analysis shows denser matrices and higher gel formation in specimens without CaO additive, while XRD analysis identified Ca(OH)2 and C-(N)-A-S-H in specimens with added CaO. FTIR analysis indicates the formation of aluminosilicate materials and water presence. The study underscores the need for further research on various CaO content in fly ash geopolymers, optimizing mix design, and understanding CaO's presence in geopolymer formation.

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