Civil & Environmental Engineering

Permanent URI for this communityhdl:10365/32547

Research from the Department of Civil & Environmental Engineering. The department website may be found at https://www.ndsu.edu/ce/

The Civilian is the newsletter for the Department of Civil Engineering and can be found at https://hdl.handle.net/10365/28260

Browse

Now showing 1 - 20 of 103

ADYTrack: A Model for Structural Analysis of Railroad Trackbed Using Random Finite Element Method
(North Dakota State University, 2019) Arshid, Asif
Railroads are playing pivotal role to the economic growth of United States and trackbeds ensure their safe and smooth operations. However, reliable trackbed performance prediction has always been challenging due to many reasons, for instance materials characterization, deteriorations of materials and geometries due to railways operation and environmental changes etc. All these factors exhibit varying levels of intrinsic variabilities and uncertainties. These variations and uncertainties are completely ignored in most of the state-of-the-practice problems due to lack of availability of robust models that can characterize variations in materials, geometries, and/or loadings. In this study, a Random Finite Element based three-dimensional numerical model, named ADYTrack, is developed for structural analysis of railroad trackbeds. Uniqueness of this model is the inclusion of materials’ intrinsic variabilities, geometric imperfections and/or uncertainties in axle loadings. The ADYTrack results, when compared with the analytical solution of a cantilever beam model, produced a maximum percentage difference of 0.7%; and 6% difference when compared with ANSYS software results for a single layer trackbed model; and a range of 5-20% difference was observed when validated against the actual field measurements. Sensitivity studies using RFEM based ADYTrack revealed that with the increasing variations in input parameters, measured by coefficient of variations (COV), the variations in output parameter also increased, and generally followed a bilinear trend with first linear component relatively insensitive up to around 30% COV of input parameters. However, beyond this limit, a considerable increase was observed in COVs of output parameters. For a COV of 80% in subgrade resilient modulus, a COV of 65% in vertical stress at the top of subgrade layer was observed. Additionally, the performance of any substructure layer found to be more sensitive to the variations in its own resilient modulus values. Furthermore, resilient modulus of subgrade layer was found to be the most influential input parameter, as revealed by many other studies, and so was its variations. To conclude, ADYTrack model can serve as a robust supplemental tool for railroad trackbed analysis, especially at locations that exhibit higher degrees of uncertainties and thus pose higher risk of public or infrastructure safety.
Alginate Encapsulated Nanoparticle-Microorganism System for Trichloroethylene Remediation
(North Dakota State University, 2012) Shanbhogue, Sai Sharanya
Nanoscale zero-valent iron (NZVI) particles were encapsulated in calcium alginate capsules for application in environmental remediation. TCE degradation rates for encapsulated and bare NZVI were similar indicating no adverse effects of encapsulation on degradation kinetics. Microorganisms were separately encapsulated and used along with encapsulated NZVI and co-encapsulated in calcium alginate capsules. Batch experiments were performed to test the efficacy of the combined iron-Pseudomonas sp. (PpF1) system. The combined system removed 100% TCE over the first three hours of the experiment followed by 70% TCE removal post TCE re-dosing. Complete reduction of TCE was achieved by NZVI between 0-3 h and the second phase of treatment (3-36 h) was mostly achieved by microorganisms. Experiments conducted with co-encapsulated NZVI-D.BAV1 achieved 100% TCE removal. During the first three hours of the experiment 100% TCE removal was achieved by NZVI, and 100% removal was achieved post re-dosing where D.BAV1 accomplished the treatment.
Analyses of Highway Project Construction Risks, Performance, and Contingency
(North Dakota State University, 2010) Diab, Mohamed F.
Past studies have highlighted the importance of risk assessment and management in construction projects and transportation industry, and have identified cost and time as the most important risks that transportation professionals want to understand and manage. The main focus of this study is to comprehensively analyze transportation construction risk drivers and identify the correlation of the significant risk drivers with project characteristics, cost growth, schedule growth, and project contingency. This study has adopted 31 relevant and significant programmatic and project-specific risk drivers from different past studies. These risk drivers have been analyzed and evaluated using survey responses from professionals in the context of highway transportation projects. Risk assessments including rating of the encountered risk drivers and their correlation with project characteristics have been carried out within the context of highway construction projects in the United States. Correlations of the construction project performance or risk measures, cost growth percentage, and schedule growth percentage, with the rating values of identified risk drivers values have enabled a better understanding of the impacts of risks and the risk assessment process for highway transportation projects. The impact of significant risk drivers on reported construction cost contingency amounts has also been analyzed. The purpose of this effort was to assess impact of ratings for cost impact, schedule impact, and relative importance of the identified risk drivers on contingency amounts. Predetermined method is the common way to calculate contingency amount in transportation projects. In this study parametric modeling has been used to analyze the relationship between predetermined contingency amounts in transportation projects with perceived risk rating values in order to understand how the expert judgments regarding risk ratings can be used in determination of contingency amounts.
Analyses of Highway Project Construction Risks, Performance, and Contingency
(North Dakota State University, 2010) Mohamed, Fahmy Diab
Past studies have highlighted the importance of risk assessment and management in construction projects and transportation industry, and have identified cost and time as the most important risks that transportation professionals want to understand and manage. The main focus of this study is to comprehensively analyze transportation construction risk drivers and identify the correlation of the significant risk drivers with project characteristics, cost growth, schedule growth, and project contingency. This study has adopted 31 relevant and significant programmatic and project-specific risk drivers from different past studies. These risk drivers have been analyzed and evaluated using survey responses from professionals in the context of highway transportation projects. Risk assessments including rating of the encountered risk drivers and their correlation with project characteristics have been carried out within the context of highway construction projects in the United States. Correlations of the construction project performance or risk measures, cost growth percentage, and schedule growth percentage, with the rating values of identified risk drivers values have enabled a better understanding of the impacts of risks and the risk assessment process for highway transportation projects. The impact of significant risk drivers on reported construction cost contingency amounts has also been analyzed. The purpose of this effort was to assess impact of ratings for cost impact, schedule impact, and relative importance of the identified risk drivers on contingency amounts. Predetermined method is the common way to calculate contingency amount in transportation projects. In this study parametric modeling has been used to analyze the relationship between predetermined contingency amounts in transportation projects with perceived risk rating values in order to understand how the expert judgments regarding risk ratings can be used in determination of contingency amounts.
Analysis and Evaluation of the Pedestrian Hybrid Beacon in School Zones
(North Dakota State University, 2010) Bittner, Michael Howard
Meeting dual objectives of pedestrian safety and motorist convenience at pedestrian crossings in school zones is an important and continuing challenge for all local communities. Pedestrian safety is influenced by pedestrian delays as well as motorist compliance of controls. Motorist convenience is influenced by the delay experienced by drivers. Conventional crosswalk control devices such as marked crosswalks and pedestrian signals are not always adequate or efficient in balancing these two crucial but conflicting objectives. The 2009 edition of the Manual on Uniform Traffic Control Devices (MUTCD) has paved the way for the use of a brand new crosswalk control device known as the pedestrian hybrid beacon (PHB). Previous research has provided evidence of this device's effectiveness in the area of motorist compliance and reduced motorist delay compared to traditional pedestrian signals. No prior research has been conducted on the PHB in the school zone context or on children pedestrians in general. This research has two objectives. The first objective was to analyze MUTCD Warrant 5 standards, which are designed for pedestrian signals in school zones, and the new PHB standards. This analysis will use pedestrian volume, vehicle volume, and gap availability on different test locations to conduct a comparative analysis of the two sets of standards. The purpose of this objective is to determine the transferability of the new MUTCD PHB standards in the school zone context. The second objective of this research was to evaluate three crosswalk control devices; marked crosswalks, pedestrian signals, and PHBs, for their ability to effectively address pedestrian safety and motorist convenience at school crossings. It was found that the PHB performed significantly better than traditional marked crosswalks but not markedly different than conventional pedestrian signals in the ability to balance the objectives of pedestrian safety and motorist convenience. The absence of improvements in performance of the PHB when compared to the pedestrian signal can be attributed to the fact that only 8.8% of motorists correctly utilized the PHB at the test location in Fargo, North Dakota. The most significant contribution of this thesis was finding that the current PHB standards in MUTCD are not transferable to the school zone context. For PHBs to be considered a viable option for engineers designing and controlling school crosswalks, it is essential that the MUTCD have school zone specific standards or guidance. The analysis carried out in this research provides insights into how such standards can be established and applied.
Analysis on Structural Modeling for Recycled Asphalt Pavement used as a Base Layer
(North Dakota State University, 2015) Noureldin, Ehab Magdy Salah
Reusing RAP in the base layer became a common practice in the last decade. However, some crucial issues must be resolved to succeed in using RAP satisfying the standard specifications as a base layer. The most important unknown factor is the mechanistic behavior of RAP. This question may be satisfied by understanding the role of RAP in terms of whether it just behaves as a black rock or has a stabilizing effect with traditional aggregates used for base layer. The first stage of this study is modeling the structural behavior of RAP via prediction MR. This stage then comprises comparing the predicted results to actual measured data under several field conditions. The second stage focuses on the modeling behavior of PD. This stage takes in consideration two sets of data, the first is for the measured PD data calculated from MR test. While another traditional set of measured data for PD from repeated tri-axial loading (RTL) test either single or multi-stage is collected for the same RAP sources used in the first stage. The third stage concerns on MR-PD relationship. It indicates the typical relationship for the MR-PD behavior that can be understood for the RAP in base layer. The fourth and last stage is essential to investigate the Poisson’s ratio of RAP blends and its effectiveness on both parameters MR and PD. This ratio is measured during un-confined compression test. Two main testing conditions: various water and RAP contents are taken in consideration during this measurement for different RAP/Aggregate sources. This study proves that both prediction models used in the MEPDG for prediction of both parameters MR and PD are totally significant for RAP/Aggregate blends used for pavement base layer. The prediction is at the highest accuracy at water content levels close to OMC%, MDD and with 50% to 75% RAP content. In addition, it is proved that Poisson’s ratio is an effective parameter on both MR and PD parameters especially with variation of water content. This conclusion recommends to take in consideration Poisson’s ratio as an effective parameter in MR and PD prediction models used in MEPDG software.
An Anisotropic Damage Mechanics Model for Concrete with Applications for Fatigue Loading and Freeze-Thaw Effects
(North Dakota State University, 2013) Reberg, Andrew Steven
It is well known that the formation and propagation of microcracks within concrete is anisotropic in nature, and has a degrading effect on its mechanical performance. In this thesis an anisotropic damage mechanics model is formulated for concrete which can predict the behavior of the material subjected to monotonic loading, fatigue loading, and freeze-thaw cycles. The constitutive model is formulated using the general framework of the internal variable theory of thermodynamics. Kinetic relations are used to describe the directionality of damage accumulation and the associated softening of mechanical properties. The rate independent model is then extended to cover fatigue loading cycles and freeze-thaw cycles. Two simple softening functions are used to predict the mechanical properties of concrete as the number of cyclic loads as well as freeze-thaw cycles increases. The model is compared with experimental data for fatigue and freeze-thaw performance of plain concrete.
Application of Damage Mechanics to Describe the Behavior of Concrete under Fatigue and Freeze-Thaw Processes
(North Dakota State University, 2015) Saboori, Ashkan
Concrete has been used in dams, bridges, and highway pavements in which freeze-thaw process and cyclic loading are important factors affecting its mechanical behavior. Damage caused by frost expansion is a primary concern when designing concrete structures in cold regions. The onset of damage within concrete can be accelerated when a freeze-thaw cycle occurs while a structure is subjected to an external loading. Also, concrete under fatigue loading gradually loses its strength with an increase in the number of load cycles. It is widely accepted that concrete shows more flexible behavior under freeze-thaw process and fatigue loading due to wide-spread microcracks occurred during both conditions. Therefore, concrete deteriorates under such processes and its mechanical properties such as strength, stiffness, and ultimate strain will change. In order to predict the mechanical behavior of concrete under such circumstances, a rate independent model is extended to cover fatigue loading and freeze-thaw cycles.
Artificial Intelligence-Empowered Structural Health Monitoring, Damage Diagnosis, and Prognosis of Metallic Structures
(North Dakota State University, 2022) Zhang, Zi
etallic structures are the key backbone of the society and economy, which are often subjected to different types of loadings resulting cracking, corrosion, and other material discontinuity, and affecting structural integrity and safety. Therefore, ultrasonic guided wave (UGW) has been widely used for structural health monitoring (SHM) to gain a deep understanding of structural performance, assess the current state of structural conditions, and avoid potential catastrophic events. Despite advances in technologies and methods in data process, microdamage detection still posts great challenges in their detectability. Different from conventional physics-based methods, artificial intelligence and machine learning (AI/ML) has recently fueled profound automation solutions toward signal process and data fusion, thereby dramatically overcoming the limits. Along this vein, this study aims to propose AI-empowered SHM framework by decoding the UGW to uncover complex interconnected information among data, models, uncertainty, and risk for enhanced structural diagnosis and prognosis to improve metallic structural integrity and safety. Several structural cases, from one-dimensional plates/rods to three-dimensional pipes, were deliberately selected to demonstrate the real-world applications. Three different levels of the AI/ML approaches, from shallow learning to deep learning, are used to explore the effectiveness of the data fusion and data representation. Meanwhile, noise interference and structurally initial nonlinearity as typical structural uncertainty are included in data collection to understand the effects of data quality and uncertainty on the robustness of the proposed methods. The results showed that the proposed method was an efficient and accuracy way to identify the damage characteristics. Results from the shallow learning demonstrated that different features had certain levels of sensitivity to damage, while the feature selection method in the shallow learning revealed that time-frequency features and wavelet coefficients exhibited the highest damage-sensitivity. However, with the increase of noise level, the shallow learning failed in detectability. By taking advantage of higher automation in feature extraction, the deep learning exhibited significant improvement in accuracy, robustness, and reliability for structural diagnosis and prognosis. Particularly, the higher-layer architecture could outperform the shallow learning in terms of higher effective and efficient data fusion, and enhanced their capability in decoding information over noise interference and structural uncertainty.
Assessment of Molecularly Imprinted Polymers as Phosphate Sorbents
(North Dakota State University, 2017) Ritt, Cody
Wastewater effluents and agricultural runoff are major sources of phosphorus overloading in surface waters. Phosphorus overloading ignites eutrophication, which devastates aquatic ecosystems. On the other hand, phosphorus, which is currently produced from phosphate rock, is a critical component of fertilizer mixes. However, the world is predicted to face a shortage of phosphate supply beyond 2033 due to unsustainable mining. This research aims to develop a polymeric sorbent that recovers low-concentration phosphorus for eutrophication prevention and fertilizer reuse. Available polymer-based products have underwhelmed expectations by having poor selectivity or lacking appropriate biodegradation rates. This research identified molecularly imprinted polymers (MIPs) as possible sorbents for overcoming the deficiencies of reported technologies. Screening of several MIPs resulted in one potentially feasible MIP for phosphate sorption. Further studies showed a sorption capacity of ~28 mg PO43--P/g and partial phosphate-selectivity. Potential phosphate removal mechanisms were identified, providing foresight into MIPs’ viability as phosphorus sorbents.
Bonding Performances of Epoxy-Based Composites Reinforced by Carbon Nanotubes
(North Dakota State University, 2022) Zhang, Dawei
Epoxy resin has been exclusively used in many civil engineering applications such as adhesive joints and anti-corrosive coatings, but most of the usages of epoxy resin highly rely on a solid adhesive bonding between the epoxy matrix and the substrate material. In order to improve the bonding performance of epoxy resin, carbon nanotubes (CNTs) are incorporated into the epoxy resin due to their extraordinary mechanical properties. Although CNTs are expected to be promising additives for epoxy resin, the reinforcing efficiency of CNTs is still far from satisfactory, the bonding performance of CNT reinforced epoxy composites remains an essential research issue. In this dissertation, a systematic study was carried out to investigate the bonding performances of epoxy-based composites reinforced using CNTs. The influences of two main influential parameters (surface roughness and bondline thickness) on the bonding performance of epoxy-based composites were examined. It was found that rougher steel substrates or thinner epoxy bondlines yielded better bonding performances for both unreinforced and CNT reinforced epoxy composites. However, according to the SEM image analyses, the reinforcing efficiency of CNTs was restricted by the non-uniform dispersion of CNTs in the epoxy matrix resulted from CNT agglomeration and entanglement. Given that the great variances of CNT geometries may inevitably result in extensive differences on CNT dispersion status and reinforcing efficiencies in CNT reinforced epoxy composites, the dispersion characterizations and bonding performance of CNT reinforced epoxy composites with different CNT geometries were studied. The experimental results indicated that CNTs with larger diameter (50-100 nm) had a greater ability to achieve more uniform dispersion which further led to better bonding performance. Although CNT length did not have an evident effect on the CNT dispersion, epoxy-based composites reinforced by normal-length CNTs (5-20 μm) had higher bonding strength and toughness than those by shorter CNTs (0.5-2 μm). To further improve the dispersion effectiveness of CNTs, a novel CNT mixing method using carboxymethyl cellulose (CMC) was proposed. It was proved that better CNT dispersion resulted from the CMC surface treatment significantly improved the bonding performance of CNT reinforced epoxy composites.
Bounding Surface Approach to the Fatigue Modeling of Engineering Materials with Applications to Woven Fabric Composites and Concrete
(North Dakota State University, 2011) Wen, Chao
It has been known that the nucleation and growth of cracks and defects dominate the fatigue damage process in brittle or quasi-brittle materials, such as woven fabric composites and concrete. The behaviors of these materials under multiaxial tensile or compression fatigue loading conditions are quite complex, necessitating a unified approach based on principles of mechanics and thermodynamics that offers good predictive capabilities while maintaining simplicity for robust engineering calculations. A unified approach has been proposed in this dissertation to simulate the change of mechanical properties of the woven fabric composite and steel fiber reinforced concrete under uniaxial and biaxial fatigue loading. The boundary surface theory is used to describe the effect of biaxial fatigue loading. A fourth-order response tensor is used to reflect the high directionality of the damage development, and a second-order response tensor is used to describe the evolution of inelastic deformation due to damage. A direction function is used to capture the strength anisotropic property of the woven fabric composite. The comparisons between model prediction results and experimental data show the good prediction capability of models proposed in this dissertation.
Building Envelope Containing Phase Change Materials for Energy-Efficient Buildings
(North Dakota State University, 2021) Li, Mingli
Energy consumption in the building sector has increased dramatically over the past two decades. The incorporation of phase change materials (PCMs) into building envelopes is considered as effective thermal energy storage to improve building thermal performance and reduce space heating/cooling load. Despite significant efforts in PCMs technologies and their application to buildings, how to select proper PCMs for buildings and maximize the activation of their latent heat to effectively improve building energy efficiency still post great challenges. The lack of systematic and comprehensive studies in these gaps hinders their broad applications in the building sector. This study aims to develop a holistic framework through experimental and numerical studies to gain a deep understanding of the thermal property of PCM and the heat transfer mechanism of the exterior wall integrated with PCM. A novel shape-stabilized paraffin/expanded graphite(EG) composite is prepared and its thermal behavior is investigated through thermal energy storage and heat transfer test. The impact of critical design parameters including the location, thickness, latent heat, melting point, and thermal conductivity of PCM on the thermal performance of a multilayer wall is explored using COMSOL Multiphysics® software. The thermal storage and heat transfer test show that EG can significantly enhance the heat transfer rate of paraffin. In addition, the paraffin/EG composite possesses favorable thermal energy storage ability to decrease the indoor temperature fluctuation and shift the peak load. Among the aforementioned design parameters, melting point of PCM is critical to significantly influence the building thermal performance. To effectively account for melting point of PCM and enhance the service efficiency of PCM, a new wall configuration containing PCM with hybrid melting points is proposed. The proposed wall assembly is found to benefit the indoor thermal comfort and the activation of the latent heat of PCM when the ambient temperature covers cold, mild, and hot loading conditions for the long term. Moreover, coupling vacuum insulation panels (VIP) with extremely low thermal conductivity and PCMs with a large amount of latent heat in the building envelope is another solution to further enhance building thermal performance due to the increased thermal insulation and thermal inertia.
Calibrating Smartphones for Monitoring Road Condition on Paved and Unpaved Roads
(North Dakota State University, 2018) Hu, Liuqing
Transportation agencies report the localization of roadway anomalies that could cause serious hazards to the traveling public. However, the high cost and limitations of present technical prevent scaling the road monitoring to all roadways. Especially the unpaved road, because of the complexity of unpaved road. Using smartphone application as road condition data collection tool offer an attractive alternative because of its potential to monitor all roadways in real time and its low cost. However, the sensor sensitivity and sampling frequency of different smartphones may vary significantly, which challenge the confidence of using smartphones for actual pavement condition assessment applications. This study tends to solve this challenge by calibrating different smartphones using two different calibrating methods including calibrating towards reference or average road roughness.
Carboxymethyl Cellulose Surface Treatment Method to Disperse Carbon Nanotubes in Smart Cementitious Materials
(North Dakota State University, 2019) Yang, Xinyuan
An innovative surface treatment method was proposed using carboxymethyl cellulose (CMC) to surface-treat carbon nanotubes (CNTs) for a consistent dispersion in cementitious materials to achieve high force detection sensitivity. This CMC surface treatment method was compared with two traditional methods, direct mixing and surfactant surface treatment, to validate dispersion effectiveness. Experimental results demonstrated that CMC and CNTs combined can increase force sensitivity of the smart cementitious material more than six times compared with direct mixing and more than three times compared with the surfactant surface treatment. CMC surface treatment significantly improved CNTs dispersion consistency. For CMC surface treatment, the comparison of 0.1%, 0.3% and 0.5% of CNTs by weight to cement demonstrated all percentages showed consistent laboratory dynamic force sensing results. Furthermore, CNTs percentage did not differ for force sensitivity. All experiments indicated the proposed CMC surface treatment method is an effective dispersion method for CNTs in smart cementitious materials.
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.
Characterization of Mechanical Adhesion Failure in Epoxy Nanocomposites by Acoustic Emission Method
(North Dakota State University, 2021) Pearson, Matthew William
Polymeric nanocomposite coatings are used to protect metallic components in a variety of civil structures from corrosive agents. The adhesion between a coating and its substrate is not yet fully understood. In this study, the relationship between mechanical delamination of epoxy coating systems and the acoustic noise generated during failure was explored using acoustic emission. Three metrics were compared: a) mechanical loading data, b) post-test image processing, and c) acoustic emission data to gain insight into the coating-substrate layer. Neat epoxy and three epoxy nanocomposite systems modified with carbon nanotubes (CNTs), graphene (GNPs), and silica (SiO2) were casted on mild steel at two different thicknesses via draw-down bar. Test results demonstrated that there was a correlation between mechanical adhesion/cohesion strength and resulting acoustic noise. The findings suggested that the higher thickness in the reinforced coatings provided for a greater cohesion failure area as well as higher volume of acoustic energy.
Characterization of Surface Microtopography and Determination of Hydrotopographic Properties
(North Dakota State University, 2012) Chi, Yaping
Spatial characterization of surface microtopography is important in understanding the overland flow generation and the spatial distribution of surface runoff. In this study, fractal parameters (i.e., fractal dimension D and crossover length l) and three hydrotopographic parameters, random roughness (RR) index, maximum depression storage (MDS), and the number of connected areas (NCA), have been applied to characterize the spatial complexity of microtopography. Clear and meaningful relationships have been established between these parameters. The RR was calculated as the standard deviation of the processed elevation, and the fractal parameters were calculated with the semivariogram method. The puddle delineation program was applied in this study to spatially delineate soil surface and to accurately determine MDS and NCA. It has been found that fractal parameters can better characterize surface microtopography. More importantly, fractal and anisotropic analyses can help to better understand the overland flow generation process.
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.
Coating of NZVI Particles With Modified Starch: Colloidal Stability and Nitrate Reduction Studies
(North Dakota State University, 2015) Pate, Mary Francis
Nanoscale-zero valent iron (NZVI) is an effective groundwater remediation media because it can quickly reduce and absorb contaminants. However, NZVI quickly agglomerates in aqueous systems, reducing its remediation capacity. This work investigated coating NZVI with native and modified rice, wheat, maize, and tapioca starches to improve colloidal stability. Colloidal stability studies were conducted with native and commercially available starches; tapioca starch modified with 2-Octen-l-ylsuccinic anhydride (OSA) was the best. Four concentrations of OSA-tapioca starch were prepared (3, 15, 35, and 50% w/w). NZVI coated with 35% OSA-modified tapioca starch (concentration = 10 g L-1) kept 66% of the coated particles suspended after 2 hours (compared to 4% of bare particles, p = 0.000). Bare NZVI reduced significantly more nitrate (20 mg L-1) than coated NZVI (p =0.000). Bare and coated NZVI provided the same nitrate reduction at 40 and 60 mg L-1 (p = 0.939 and p = 0.815, respectively).

Browse

Browsing Civil & Environmental Engineering by Title