Graduate Thesis Or Dissertation
 

Evaluation of Serratia Ureilytica as a Greener Unsealed Road Stabilization Method

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6682xb66j

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  • Covering half of South America, Brazil is one of the largest agricultural and commercial forest producers globally, with a correspondingly complex road network necessary to support the production and marketing processes of such goods. Contrary to global statistics, almost 90% of the country’s road network is classified as unsealed or dirt roads (CNT, 2020). This dissertation briefly reviews the history of such roads and explores the construction standards of unsealed roads in Brazil, showing how such standards can affect adjacent water bodies through hydric erosion and sedimentation. Specifically, this dissertation analyzes Serratia ureilytica as an innovative biocement formed through the process of Microbiologically Induced Calcium Carbonate Precipitation (MICCP) and serving as a potential new alternative to stabilize unsealed roads, thus reducing hydric erosion and minimizing sedimentation. To test the effectiveness of this method, we compared our novel MICCP protocol to three classic methods of unsealed road stabilization: granulometric stabilization, cement, and hydrated lime, as adopted by Brazilian’s road construction standards. We simulated and compared the effects of these four stabilization methods on 1) surface erosion due to percolation effects from piping erosion and 2) water quality impacts from sedimentation due to traffic resistance of the unsealed roads. This study tested the biocementation effects of S. ureilytica over unsealed road grades (URG) determined as A, C and F by the Brazilian standards for unsealed road construction. To contribute to the global efforts to achieve a homogeneous biocement layer, this research tested fixed volumes of biocementation solution with variable granulometric distributions, in addition to testing the traditional stabilization methods of compaction, cementation, and hydrated lime addition. The greatest rate reduction in permeability was achieved for unsealed road grade (URG) F, which has the highest content of fine particles. A permeability rate reduction of 98.25% was achieved with the application of biocement when complared to granulometric stabilization with no sample compaction, and 95.64% reduction when compared to granulometric stabilization with sample compaction. URG A and URG C samples showed similar behavior after the biocementation treatments. Cement treatments were 100 % impervious for all samples, and hydrated lime treatments were less effective at reducing permeability rates than biocementation treatments. Our main findings lead to the conclusion that S. ureilytica is a strong candidate as a potential alternative method for unsealed road stabilization through the biocementation process. Our results gave enough evidence and data to expand the research to field scale, where the granulometric distribution proposed adaptations can be tested under all variables involved in unsealed road construction and use. Our secondary study was designed to test potential markers to evaluate the potential environmental impacts from erosion of chemically stabilized unsealed roads, focusing on how the stabilization methods may impact water quality. Cement and hydrated lime are the two most commonly used stabilizers to improve unsealed roads. Calcium, magnesium, and silicon were selected as potential markers since they are the most abundant ions in cement, hydrated lime and biocement, and low-cost tests are available to determine their concentrations in samples. The levels of calcium and magnesium found in percolated water from the test samples in this study could serve as indicators of increased sediment from road erosion which carries other toxic chemicals, heavy metals, and petrochemicals due to road traffic, contributing to the pollution of water bodies and potential public health concerns. Further research in the field is needed to test for the presence of specific road pollutants in adjacent waterways under variable conditions of traffic flow and weatherization. The silicon lixiviated from the unsealed roads can be recycled and reused as a valuable source for agriculture and the regeneration of aquatic systems. Future research should include the research to field scale, adding all variables that may affect road weatherization and its erosion process, plus complete water quality assessment, including heavy metals, dissolved oxygen, turbidity, and sediment levels to test the connections and correlational parameters that would support the use of calcium, magnesium, and silicon as potential indicators of water quality pollution from unsealed roads. Silicon extraction and reuse costs should also be addressed.
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  • scholarship (Process n.: 8453/13-6) and financial funding (Process n.: 472393-2013/8) from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Coordination for the Improvement of Higher Education Personnel, a Brazilian federal government agency under the Ministry of Education), Brazil.
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  • Intellectual Property (patent, etc.)
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  • 2022-01-03 to 2023-02-03

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