ORCID Identifier(s)

0000-0001-7810-6807

Graduation Semester and Year

2021

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Warda Dr. Ashraf

Abstract

The most energy-intensive manufacturing industry in the US is the Ordinary Portland Cement (OPC) industry. This industry is responsible for 5-8% of global CO2 emissions caused by humans. The calcination of limestone to produce high lime calcium silicate and high manufacturing temperature (1450°C) are responsible for this significant amount of CO2 emissions. This CO2 footprint of the cement-based composites can be decreased by utilizing cementitious materials with low-lime calcium silicate. Low-lime calcium silicates are typically semi-hydraulic or non-hydraulic. As a result, it is necessary to activate those materials in order to increase their reactivity. Alkali activators, carbonation curing (CO2 curing), and other techniques have been shown in recent investigations to substantially increase the reactivity of those materials. Calcium silicate combines with CO2 in the presence of water to produce CaCO3 and calcium-modified silica gel during the carbonation curing procedure. As a result of this technique, low-lime calcium silicate can now be used as an OPC replacement. This study looked into the specifics of effective carbonation curing and reaction kinetics for hydraulic, semi-hydraulic, and non-hydraulic calcium silicate. The influences of minerals and biopolymers on the carbonation curing phase were also investigated in this study. In order to construct the new binder composition successfully, an in-depth investigation into the performance of the OPC-slag blended system due to carbonation curing was conducted. This detailed investigation revealed that slag might replace 65% of OPC without degrading compressive strength. Slag accelerates the carbonation process. Slag carbonation also improves the concrete's durability by reducing permeability. Silica gel polymerization was enhanced by increasing the amount of slag and the carbonation duration. This research also shows that pre-hydration curing prior to carbonation improves mechanical and microstructural properties. The impacts of biopolymers on carbonation-activated binders were investigated in this study. When biopolymers like dopamine hydrochloride come into contact with hydraulic/semi-hydraulic calcium silicate, they polymerize and produce polydopamine. Polydopamine has a greater affinity for Ca2+ and prevents amorphous CaCO3 from clustering together. As a result, when dopamine is incorporated into a carbonate matrix, more amorphous CaCO3 is produced than calcite. The effects of cellulose nanofibers were also studied. Cellulose nanofibers can significantly improve the early age strength gain and flexural strengths of carbonated composites. Finally, the impacts of MgO-based cementitious materials on carbonated semi-hydraulic and non-hydraulic systems were studied in this section. This extensive investigation discovered that MgO-based cement produced more hydro-magnesite when mixed with non-hydraulic calcium silicate during carbonation curing. It's worth noting that hydrated magnesium carbonate has a 600% higher solid volume than magnesium oxide. Because of the substantial volume increase, the microstructure has significantly densified, and the critical pore size distribution has changed. As a result, adding MgO improves mechanical performance substantially. It also helps to increase CO2 sequestration.

Keywords

Carbonation, Biomineralization, Slag, CaCO3, Calcite, Vaterite, Aragonite, Amorphous CaCO3, Dopamine, Cellulose, Low carbon footprint.

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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