ORCID Identifier(s)

0000-0001-7365-0387

Graduation Semester and Year

2023

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Warda Ashraf

Abstract

This study introduces an innovative approach to mitigate carbonation-induced degradation of C-S-H and to enhance the carbonation properties of low calcium based cementitious materials by utilizing specific biomimetic molecules. In this study, four different biomimetic molecules were utilized. Details about their chemical formula and chemical structure can be found in Chapter 1. The dissertation is broadly focused on two aspects, Part 1 (Chapter 2 and 3) evaluated the role of biomimetic molecules in reducing the carbonation degradation of C-S-H. Part 2 (Chapter 4 and 5) assessed the effectiveness of the biomimetic molecules as performance enhancing admixture of carbonation cured dicalcium silicates. For part 1, synthetic C-S-H samples were prepared, incorporating biomimetic molecules M-1 and M-2. The impact of these biomimetic molecules on C-S-H, both before and after carbonation, was examined using various analytical techniques, such as 29Si NMR, TEM, nanoindentation, and FTIR. Without these molecules, unmodified C-S-H underwent complete polymerization into silica gel after 168 hours of carbonation. However, C-S-H modified with biomimetic molecules retained its original structure even after 28 days of carbonation. The organic molecules also substantially increased the elastic modulus of C-S-H, a property that further improved after carbonation. Furthermore, this study addresses knowledge gaps by demonstrating the application of in-situ ATR-FTIR for monitoring decalcification kinetics of C-S-H, evaluating the influence of C/S ratio, pH, and the presence of M-1 on decalcification kinetics, and monitoring in-situ CaCO3 formation and polymorph conversion during C-S-H carbonation for various experimental conditions. For part 2 of the dissertation, this research investigated the effectiveness of different biomimetic molecules, including M-1, M-3, and M-4, to enhance the properties of carbonated dicalcium silicate-based cementitious systems. Low dosages (2.5% and 5%) of these molecules were incorporated into the γ-C2S paste. XRD and SEM analysis confirmed alterations in CaCO3 polymorphs formation, with M-4 exhibiting the highest CaCO3 content. While porosity measurements from MIP and DVS were higher, the modified batches showed increased compressive and flexural strengths. Specifically, the 2.5% M-4-modified batch displayed a 61% higher compressive strength than the control batch. Additionally, 5% M-3 and 5% M-1 batches demonstrated the highest flexural strength, 53% greater than the control batch, aligning with nanoindentation results that revealed an enhanced elastic modulus due to the formation of organic-inorganic hybrid phases. Finally, the study comprehensively explores the effects of M-4 with different molecular weights (MW 2000, MW 5000, and MW 240000) and dosages (0.5%, 1%, and 2.5%) on the carbonation of β-C2S binders. It highlights the influence of M-4 on calcium carbonate (CaCO3) formation, crystal polymorphs, microstructure, and mechanical strength. MW 5000 and MW 240000 significantly promoted CaCO3 formation and controlled crystal polymorphs, particularly at the 1% dosage. The study employs various analyses to observe carbonation properties, revealing the potential of M-4-modified β-C2S to enhance microstructural integrity and mechanical properties. Even under elevated temperature curing (50°C), M-4-modified β-C2S binders maintained impressive mechanical strength, illustrating their adaptability across diverse environmental conditions. In summary, this research underscores the potential of biomimetic molecules to enhance construction materials, offering opportunities to optimize phase formation and boost mechanical properties.

Keywords

Carbonation, Biomimetic molecules, CSH, Dicalcium silicates

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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