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Dissertation
Conversion of Waste Coal Combustion Ash to Value-Added Construction Lightweight Aggregates through A Holistic Thermodynamics-Guided Manufacturing Framework
Doctor of Philosophy (Ph.D.), Drexel University
Sep 2021
DOI:
https://doi.org/10.17918/00000584
Abstract
Waste coal combustion ash (W-CCA) is one of the largest-volume industrial solid waste materials historically discarded in the U.S. The accumulation of billion tons of W-CCA in the landfills and surface impoundments have negatively impacted the environment by polluting waterways, groundwater, and drinking water. Two notable instances of W-CCA environmental damage are Kingston Fossil Plant coal fly ash slurry spill (Tennessee, 2008) and Dan River coal ash spill (North Carolina, 2014). To address this issue, this thesis studies the potential conversion of W-CCA to lightweight aggregate (LWA) that can be used in concrete industry. Accessibility of construction LWA that is traditionally produced from clay, slate, and shale is challenging for the concrete industry in some states due to the absence of local construction LWA manufacturers. Accordingly, the conversion of W-CCA into LWA will reduce the environmental impact of W-CCA, prevent the natural resource consumption, lower the CO₂ emission associated with material transportation, and help concrete producers to save money by having access to local construction green LWA. The research presented in this thesis is focused on developing a thermodynamics-guided framework to design and manufacture engineered spherical LWA (named SPoRA) from W-CCA through sintering a process for concrete applications. The thermodynamics-guided framework is founded on the universal three required conditions during sintering for successful production of a porous LWA: (i) forming sufficient amount of liquid phase (ii) achieving appropriate viscosity for the liquid-solid phase, and (iii) releasing sufficient gas to the viscos liquid from W-CCA materials to create gas filled pores in the LWA. SPoRA is manufactured at the small lab scale using two types of W-CCA: bottom ash and waste fly ash (also called as off-spec fly ash). The engineering properties of SPoRA such as mineralogy, thermogravimetric response, specific gravity, vacuum water absorption, time depended water absorption, water desorption, porosity, pore size distribution, and permeability are characterized, and the thermodynamics-guided framework is examined and validated. The promising engineering properties of SPoRA shows its suitability for applications such as concrete internal curing and structural lightweight concrete. Using the developed thermodynamics-guided framework and the knowledge developed at the lab scale, the manufacturing of SPoRA is then scaled up to lab pilot-scale using a pelletizer and rotary furnace. SPoRA from off-spec fly ash is produced in larger quantities and its engineering properties are characterized and compared to that of traditional construction LWA (i.e., slate and shale based LWA) available in the US market. The results further demonstrate that SPoRA produced using off-spec fly ash passes the ASTM C330 requirements for structural LWA and indeed possesses comparable engineering properties to that of slate and shale-based LWA. Furthermore, structural lightweight concrete is made using the manufactured SPoRA, and its fresh mechanical, and hydration properties are comparatively characterized. Lightweight concrete made using SPoRA easily passes the ASTM C330 requirements for structural lightweight concrete in terms of density and mechanical performance and has comparable overall performance to that of lightweight concrete made with traditional LWA. The lab pilot-scale production of SPoRA proposed here shows a promising potential for industrial scale production of SPoRA, thereby leading to a sustainable remedy not only for W-CCA management, but also concrete producers that need local accessibility to construction LWA.
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Details
- Title
- Conversion of Waste Coal Combustion Ash to Value-Added Construction Lightweight Aggregates through A Holistic Thermodynamics-Guided Manufacturing Framework
- Creators
- Mohammad Balapour
- Contributors
- Yaghoob Amir Farnam (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xviii, 203 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Civil (and Architectural) Engineering [Historical]; College of Engineering (1970-2026); Drexel University
- Other Identifier
- 991015606266804721