ORCID Identifier(s)

0000-0002-7307-3855

Graduation Semester and Year

2019

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Anand Puppala

Abstract

Expansive soils have been stabilized using conventional soil stabilizers such as lime and cement for many decades. These conventional stabilizers form cementitious productions that enhance the strength properties and reduce the swelling and shrinkage potential of expansive soils. However, the energy-intensive production operations of conventional soil stabilizers release substantial amounts of harmful greenhouse gases into the atmosphere. In addition, conventional soil stabilizers are also prone to durability issues, which make them somewhat ineffective as long-term solutions. Furthermore, the use of calcium-based stabilizers cause excessive swelling and shrinkage in sulfate-bearing subgrade soils due to the formation of highly expansive minerals like Ettringite. This study investigates the use of geopolymers as an alternative soil stabilizer for expansive soils. Geopolymers are alumino-silicate binders that have received much attention as a sustainable alternative to conventional chemical additives. Geopolymers have high compressive strengths and can be processed at room temperatures from aqueous solutions by utilizing waste materials (e.g. fly ash) or abundant natural sources (e.g. clay). Geopolymers have been investigated by a few researchers for the purpose of soil stabilization, although most studies were performed on non-expansive soils and focused solely on the ability of geopolymers to enhance soil strength. This study evaluates the performance of a metakaolin-based geopolymer in enhancing strength/stiffness, volume change, and long-term performance characteristics of expansive soils. The objective of this research is to synthesize a metakaolin-based geopolymer and evaluate its efficiency as the sole binder to stabilize expansive soils. Two expansive soils from north Texas were obtained and treated with the in-house synthesized metakaolin-based geopolymer at different dosages for different curing periods. The following tasks were outlined to accomplish the objectives of this research: (1) synthesize metakaolin-based geopolymer and treat expansive soils with three different dosages, (2) perform basic, chemical, engineering, and mineralogical testing of control and geopolymer-treated soils, (3) treat expansive soils with lime to compare with geopolymer treatment, (4) analyze test results to evaluate efficiency of geopolymer to improve expansive soils, and (5) assess and compare sustainability and resiliency benefits of geopolymer and lime treatment for expansive soils. Three dosages of the in-house synthesized metakaolin-based geopolymer was applied to both expansive soils and tested for different properties. The geopolymer dosages applied in this study are defined as the percentage weight of metakaolin in the geopolymer, with respect to the dry weight of soil to be treated. Geopolymer treatment was found to decrease the plasticity index of the expansive soils, with increasing dosage and curing period. Significant strength and stiffness enhancement was observed in geopolymer-treated soils. Negligible swelling and shrinkage potential were observed in soils treated with just low geopolymer dosages. Modified durability and leachability tests conducted revealed low strength loss in geopolymer-treated soils. Strength, swell, and modified durability test results of lime-treated soils were found to be comparable to results from geopolymer-treated soils. Microstructural studies provided insight into geopolymer gel formation that explains the enhanced macro-behavior of geopolymer-treated soils. Additionally, sustainability and resiliency assessment studies showed that geopolymers have a much lower impact on the environment than lime. Metakaolin-based geopolymers are evidently found to be quite efficient in stabilizing expansive soils. It is expected that the present research findings will be valuable for future investigations and design implementations of geopolymers as a more sustainable and ‘green’ alternative to conventional soil stabilizers.

Keywords

Geopolymers, Soil stabilization, Expansive soils, Ground improvement

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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