Kalpana Katti - Thesis Committee

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    Characterization of Activities of Crumb Rubber in Interaction with Asphalt and its Effect on Final Properties
    (North Dakota State University, 2015) Ghavibazoo, Amir
    Recycling of millions of scrap tires produced everyday is crucial challenge encountered by waste management systems. Recycling tire rubbers in form of ground tire rubber, known as crumb rubber modifier (CRM), in asphalt industry was introduced in early 1960's and is proved as an effective recycling method. Interaction between CRM and asphalt is physical in nature which happens mainly due to exchange of components between CRM and asphalt and enhances the time temperature dependant properties of asphalt. In this work, the interaction between CRM and asphalt was evaluated through monitoring the evolutions of CRM in asphalt in macro and micro-level. The mechanism and extent of CRM dissolution were monitored under several interaction conditions. The composition of materials released from CRM was investigated using thermo-gravimetric analysis (TGA). The molecular status of the released components were studied using gel permeation chromatography (GPC) analysis. The composition analysis indicated that the CRM start releasing its polymeric components into the asphalt matrix at dissolutions higher than 20%. The released polymeric component of CRM alters the microstructure of the asphalt and creates an internal network at certain interaction temperatures according to viscoelastic analysis. At these temperatures, the released polymeric components are at their highest molecular weight based on GPC results. The effect of released components of CRM on the time temperature dependent properties of asphalt and its glass transition kinetic was monitored using dynamic shear rheometer (DSR) and differential scanning calorimetry (DSC), respectively. The DSC results showed that the intensity of glass transition of the asphalt binder which is mainly defined by the aromatic components in asphalt reduced by absorption of these components by CRM. The evolution of CRM was investigated during short-term aging of the modified asphalt binder. In addition, the effect of presence of CRM and release of its component on oxidization of asphalt binder was evaluated using Fourier transform infrared spectroscopy (FTIR). The results revealed that CRM continue absorbing the aromatic components of asphalt during aging which stiffen the asphalt binder. Also, it was observed that release of oily components of the CRM, which contain antioxidant, reduces oxidization rate of asphalt significantly.
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    Enhancement of Dispersibility of Zero-Valent Iron Nanoparticles for Environmental Remediation: Entrapment and Surface Modification with Polymers
    (North Dakota State University, 2012) Krajangpan, Sita
    Nanoscale zero-valent iron (NZVI) particles have been surface modified and used for contaminant remediation. NZVI tend to agglomerate due to magnetic and van der Waals forces and form larger particles that settle down in aqeous media. Agglomerated particles increase in size and have decreased specific surface area and that lead to decrease in their reactivity. In this research, polymer-based surface modifiers were used to increase dispersibility of NZVI for environmental remediation applications. Ca-alginate was selected to entrap NZVI in beads and used to remove aqueous nitrate. The two-way ANOVA test indicates that there was no significant difference between reactivities (towards nitrate) of entrapped NZVI and bare NZVI. While the reactivity of entrapped NZVI was comparable to bare NZVI, the NZVI particles were found to remain agglomerated or clustered together within the alginate beads. A novel amphiphilic polysiloxane graft copolymers (APGC) was designed, synthesized and used to coat NZVI in an attempt to overcome the agglomeration problem. APGC was composed of hydrophobic polysilosin, hydrophilic polyethylene glycol (PEG), and carboxylic acid. The APGC was successfully adsorbed onto the NZVI surfaces via the carboxylic acid anchoring groups and PEG grafts provided dispersibility in water. Coating of NZVI particles with APGC was found to enhance their colloidal stability in water. The APGC possessing the highest concentration of carboxylic acid anchoring group (AA) provided the highest colloidal stability. It was also found that the colloidal stability of the APGC coated NZVI remained effectively unchanged up to 12 months. The sedimentation characteristics of APGC coated NZVI (CNZVI) under different ionic strength conditions (0-10 mM NaCl and CaCl2) did not change significantly. Degradation studies were conducted with trichloroethylene (TCE) and arsenic(V) [As(V)] as the model contaminants. TCE degradation rates with CNZVI were determined to be higher as compared to bare NZVI. Shelf-life studies indicated no change on TCE degradation by CNZVI over a 6-month period. As(V) removal batch studies with CNZVI were conducted to in both aerobic and anaerobic conditions. Increase in arsenic removal efficiency was observed with CNZVI as compare to bare NZVI in both aerobic and anaerobic conditions. Ionic strengths showed minimal inhibiting effect on arsenic removal by CNZVI.
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    Clay Fluid Interactions in Montmorillonite Swelling Clays: A Molecular Dynamics and Experimental Study
    (North Dakota State University, 2012) Patwary, Md Zillur R.
    Swelling clays cause tremendous amounts of damage to infrastructure. For the effective prevention of detrimental effects of these clays, and to optimize the beneficial properties for industrial applications it is necessary to clearly understand the fundamental mechanisms of swelling of clays. In this study, we studied the effect of fluid polarity on swelling and flow properties of swelling clays using molecular modeling and experimental technique for bridging the molecular level phenomenon of these clays with microstructure change, particle breakdown and macro scale swelling and flow properties. A wide range of fluids (Dielectric Constant 110 to 2.4) were used, those are also commonly present in landfill leachates. We were able to tie the properties of swelling clays at different length scales. Then, we simulated the solvation of clay sheets, studied the effect of discrete charge distribution, contribution of edge charges on swelling clays and discussed some fundamental assumptions associated with double layer theories.
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    An Investigation of Mechanics of Collagen and Fibril in Bone and Interactions in Swelling Clays: A Molecular and Multiscale Modeling Study
    (North Dakota State University, 2012) Pradhan, Shashindra Man
    A fundamental study of the mechanics at the molecular scale and bridging it to the continuum level through multiscale modeling is the focus of this work. This work investigates how the material properties of nanoscale systems are influenced by the nonbonded interactions and molecular conformations. The molecular model is then bridged with the finite element model to link mechanics at nanoscale with the continuum scale. This work provides an unprecedented insight into how the interactions at the molecular scale influence mechanical properties at higher scales. Two materials are considered for the molecular modeling study: bone and Na-montmorillonite swelling clay. Bone is composed of composed of collagen molecules and hydroxyapatite in the molecular scale, which are organized into collagen fibril. The molecular dynamics study is carried out to study the nature of collagen-hydroxyapatite interface and the mechanics of collagen in bone. Furthermore, the molecular model of full-length collagen is built for the first time to show the differences in its conformation and deformation mechanism during pulling as compared to the short molecules, upon which the current understanding of is based. The mechanics of collagen is explained with the help of three-tier helical hierarchy not seen in short molecules. Two mechanisms of deformation and conformational stability of collagen are proposed: (i) interlocking gear analogy, and (ii) interplay between level-1 and level-2 hierarchies, the hydrogen bonds acting as an intermediary. The multiscale model of collagen fibril is developed by bridging nanomechanical molecular properties of collagen into the finite element model. This model shows that the molecular interactions between collagen and mineral significantly affect the mechanical response of collagen fibril. The deformation mechanism of collagen fibril and the effect of collagen crosslinks are also elucidated in this study. In recent years Na-montmorillonite has been proposed for bone regenerative medicine, besides other existing engineering applications. The molecular dynamics study of Na-montmorillonite at different levels of hydration is carried out to understand the role played by molecular interactions in the swelling behavior of Na-montmorillonite. This study greatly adds to our understanding of clay swelling, and provides important insights for modeling exfoliation and particle breakdown in clay.
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    Influence of Molecular Interactions on Elastic Properties and Oxygen Diffusion in PolyButylene Terephthalate Polymer: A Molecular Dynamics Study
    (North Dakota State University, 2012) Raviprasad, Muniyamuthu
    In most barrier applications, both mechanical and diffusion properties of the material are important. In this thesis the evaluation of molecular mechanisms responsible for the enhanced elastic properties of Polymer Clay Nanocomposites (PCNs) and the molecular mechanisms of Oxygen diffusion in PolyButylene Terephthalate polymer are presented. Interaction energy between PCN constituents, conformational changes of polymer, interaction energy between Oxygen molecule and polymer, rate of Oxygen and Oxygen diffusion coefficient are evaluated. Molecular simulation studies of PolyButylene Terephthalate (PBT) clay nanocomposite and Nylon6 clay nanocomposite show that a higher crystallinity polymer such as PBT would require higher attractive and repulsive interactions with organic modifier in order to make significant change in the crystallinity of PBT in the nanocomposite and in turn enhance the elastic modulus and hardness. Molecular interactions energy between Oxygen molecule and polymer, change in polymer conformation caused by thermal energy assist the Oxygen molecule to diffuse through polymer.
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    Initial Swelling Mechanism of Expansive Clays: A Molecular Dynamics Study
    (North Dakota State University, 2012) Srinivasamurthy, Lakshmikanth
    Expansive soils are widely found in many parts of the world. Highly active smectite clay mineral Montmorillonite is the major constituent in these clays and can expand or contract up to 15 times of their original volume. Constrained swelling exert large amount of stress causing damage to structures, pavements etc. These clays are also used as barrier materials, Nano-materials in polymer clay Nano composites and drug delivery systems. Several factors influence the swelling potential such as water content, density, voids, electrolyte content and cation exchange capacity. However, molecular scale mechanisms that control swelling behavior in these clays need to be understood. Objectives of this research are to provide an insight into mechanisms that result in swelling of these clays. Molecular modeling is used to build and study solvation of Na-Montmorillonite system. Trajectories of water molecules are captured and the evolutions of interaction energies with swelling are calculated.
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    Parametric Cost Estimating and Risk Analysis of Transportation Tunneling Projects
    (North Dakota State University, 2016) Membah, Joseph F. J.
    Due to the increased scrutiny of construction costs for infrastructure projects by the public and legislators, it is becoming increasing important for project developers to prepare accurate conceptual cost estimates for transportation tunnel projects at the feasibility stage to aid in making investment decisions. Past studies have emphasized that tunnel-project costs have been significantly underestimated, and cost uncertainties and risks have been identified as the cause of cost under or overestimation. A broad understanding of the factors that contribute to cost underestimation is important as it enables researchers and estimators to develop appropriate functions, evaluate, and implement them to produce realistic cost estimates. This study was aimed at developing parametric cost estimation functions and quantifying their risks for transportation tunnel projects. A comprehensive background study of more than 39 published articles on transportation tunnel infrastructure projects was conducted through a systematic literature review and 40 key estimating parameters that may impact project costs and the associated project logistics were identified. Data from completed tunnel projects were collected and used to develop the parametric cost equations. Exploratory analyses were first performed to discover the correlations among tunnel costs and tunnel cost parameters/drivers. The purpose of this effort was to assess if a relationship existed between tunnel variables and tunnel project cost estimates. Parametric cost estimation functions were then developed for different tunnel applications. There has been no comprehensive study performed to date to develop parametric cost estimation functions that incorporated risk and uncertainty for transportation tunnel projects. Two representative sample case studies were performed and Monte Carlo simulation was used to quantify the associated risks. The results from the case studies illustrate the need to use appropriate techniques to simulate tunnel costs and quantify the risks associated with the estimates. The findings of the study provide a methodology to estimate the costs of transportation tunnels and quantify the uncertainties and risks associated with the costs. The methodology developed in this research could help reduce the incidence of project cost underestimation and alleviate some of the controversies surrounding cost overruns in transportation tunnel projects.
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    Enhancing the Performance of Crumb Rubber Modified Asphalt through Controlling the Internal Network Structure Developed
    (North Dakota State University, 2016) Ragab, Mohyeldin
    Sustainability presents a pathway for future generations to have a better life. Cradle to cradle methodology is the essence of sustainability. In cradle to cradle approach, we aim to reuti-lize a given waste instead of disposing or landfilling it. Each year, millions of waste tires are dis-posed of in landfills. This poses a major challenge environmentally and economically. Environ-mentally, those tires become prone to fire hazards as well as being a place for rodents and mos-quitos to reside at. Economically, on the other hand, each tire has an average of about 50% valu-able polymers as well as oily components. One of the methods to utilize the valuable raw materi-als in waste tires is to recycle it in the form of ground tire rubber also known as crumb rubber modifier (CRM). Although CRM has been widely used as an asphalt modifier, however, due to the complexity of asphalt as well as the waste nature of CRM, the full understanding of the CRM modification mechanism with asphalt has not been fully understood. Understanding of the modi-fication mechanisms involved in the CRM interaction with asphalt would enable us to produce a crumb rubber modified asphalt (CRMA) with enhanced properties. In the current research work, an attempt is made to better understand the mechanism of interaction between CRM and asphalt and the nature of components from asphalt and CRM that take part in the interaction between them. In addition, we investigate the effectiveness of CRM as a modifier for asphalt on the mac-ro and microscale aspects. Another part of the current research work deals with a second waste material; used motor oil. Used motor oil (UMO) presents yet another challenge to environment. With the ever increas-ing motor vehicles produced with advanced technologies and increased advanced motor oil de-mand. This presents a burden on the environment, with the continuous production of UMO. In the current research work, we investigated the feasibility of utilizing UMO as a modifier for asphalt and CRMA. We also investigated the effect of UMO on the micro and macroscale aspects of asphalt.
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    Computational Biomechanics of Blast-Induced Traumatic Brain Injury: Role of Loading Directionality, Head Protection, and Blast Flow Mechanics
    (North Dakota State University, 2015) Sarvghad-Moghaddam, Hesam
    In this dissertation, blast-induced traumatic brain injury (bTBI) is studied with respect to the blast wave directionality, mitigation capability of helmet/faceshield, and blast flow mechanics using finite element (FE) and computational fluid dynamics (CFD) schemes. For the FE study, simulations are performed on a detailed FE head model using LS-DYNA, and CFD simulations are carried out using the ANSYS-CFX to examine the underwash development by analyzing the behavior of blast flow from different directions. The following tasks are conducted. First, the effects of the loading direction on the mechanical response of the head and brain is investigated through impact and blast induced loading on the head. Due to the differences in the shape, function, and tolerance of brain components, the response of the head/brain varies with the direction of the impact and blast waves. In identical situations, the head shows to have lower tolerance to side loading. Second, the inclusion of the faceshield as a potential head protective tool against blast threats is evaluated with respect to blast direction. The helmet-faceshield and helmeted assemblies are shown to be most efficient when the head is exposed to blast from the front and top sides, respectively. Faceshield is observed to be effective only in front blast as it might impose either adverse or no effects in other directions. The shockwaves are seen to form a high pressure region in head-helmet-faceshield gap (underwash effect) which induces elevated pressures on the skull. Third, the underwash effect’s mechanism is investigated through CFD simulations of supersonic shockwave flow around the helmeted head assemblies. CFD results reveals that the backpressure is produced due to the creation of a backflow in the exterior flow on the outgoing interior flow. The bottom and side shockwave directions predict the highest underwash overpressures, respectively. Finally, the ICP and shear stress of the brain is evaluated in case of underwash incidence. FEA results show that underwash overpressure greatly changes with the blast direction. It is concluded that underwash clearly altered the tissue response of the brain as it increases ICP levels at the countercoup site and imparts elevated skull flexure.
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    Brain Tissue Mechanical Characterization and Determination of Brain Response under Confined Blasts Explosions
    (North Dakota State University, 2015) Rezaei, Asghar
    Mechanical experimental tests including stress relaxation, simple monotonic ramps, and impact loads were performed on porcine brain tissues to investigate the response of the brain under different loading scenarios. Linear viscoelastic models were employed to determine the applicability and limitations of the linear mechanical models in tension. In addition the lowest and highest stress values, which can be possibly applied to the tissue due to change in the strain rates, were investigated using stress relaxation experiments to implicitly address the two levels of strain rates. Porcine brainstem samples were tested in six stress relaxation experimental settings at strain amplitudes ranging from 5% to 30% in compression. The lowest stress was directly measured from long-term responses of stress relaxation experiments when the stress values remained constant. The highest stress level was determined by using the quasi-linear viscoelasticity theory and estimating the instantaneous stress of the samples at six strain amplitudes. It was hypothesized that there is a correlation between the two pure elastic behaviors. The hypothesis was true as a strong linear correlation was found between the two elastic responses. The results showed that the instantaneous stress values were 11 times greater than the long-term stress values, practically similar across all strain amplitudes. In the second part of the thesis, a number of computational studies were conducted using a validated human head model. The head model included major components of human head and underwent different blast scenarios in open and confined spaces. The study investigated the effect of reflections from the walls. The results show that when the head was in the vicinity of the wall, the biomechanical parameters were dramatically increased, especially in the corners. Comparing brain biomechanical parameters in confined, semi-confined, and open spaces under blast loads, the brain sustained greater stress and strain values, with larger duration of the loads, in confined spaces. Also, a primary blast injury (PBI) with a tertiary blast injury (TeBI) in a confined space was compared. The results indicated that the PBI due to the incident shock wave was much more injurious than TeBI due to blunt impact.
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    Micromechanical Characterization of Brain White Matter with Bi-Directional Orientation of Axonal Fibers
    (North Dakota State University, 2015) Shankar, Saurav
    Axonal injury within the white matter of human brain and spinal cord has led to several diseases in the Central Nervous System (Karami and Shankar, [1]). Diffuse axonal injury, one of the forms of Traumatic Brain Injury is caused due to swelling and elongation of axons in case of explosions, small and severe accidents, falling from heights where the brain gets an impact due to sudden movement of skull or hit by an object. A brain tissue model with bidirectional orientation of axonal fibers within the white matter of human brain has been developed. This brain tissue represents a repeating unit cell (RUC) modeled in ABAQUS (finite element software) [2] which comprises of axons and extracellular matrix (Karami and Shankar, [1]). Hyperelastic material properties of white matter sheet corona radiata of a porcine brain with bidirectional orientation of axonal fibers within the extracellular matrix is considered (Karami and Shankar, [1]).