Cement stabilized material used for subbase or base pavement layers has been a widely accepted practice by many state Departments of Transportation (DOTs); particularly, for DOTs with limited access to quality crushed aggregates for pavement construction. Despite over 100 years of use, construction specifications governing cement stabilized pavement layers have largely remained the same and are primarily method based specifications (i.e. individual components evaluated and construction methods prescribed) rather than evaluating or testing mechanical properties of the end product. With the recent emergence of the Plastic Mold compaction Device (PM Device), multiple agencies are looking to depart from method based soil-cement specifications by implementing the PM Device for design and construction quality control and quality assurance (QC/QA) testing. Prior to this dissertation, PM Device protocols have been validated under lab conditions but only limited field validation had been performed. Additionally, time delay between initial mixing and compaction of cement stabilized soils is a known issue, which can affect compaction of PM Device specimens as well as construction target density values determined through AASHTO T134 Proctor testing. The main objectives of this dissertation are to investigate time delay effects on cement stabilized soil compactability during Proctor testing, develop a nationally recognized Standard Practice for PM Device specimen fabrication, and perform PM Device field evaluations for QC/QA testing. Lab experiments were conducted to investigate time delay effects and finalize PM Device Standard Practice protocols. Five field projects were evaluated to validate PM Device QC/QA applications and Standard Practice protocols in a construction environment. Time delay was observed to have a notable detrimental influence on compactability during AASHTO T134 Proctor testing and PM Device specimen fabrication. Recommended guidance was provided to characterize compaction delay effects. AASHTO PP92-19 was developed and published by AASHTO's Committee on Materials and Pavements to standardize specimen fabrication for the 3x6 inch and 4x8 inch versions of the PM Device. The PM Device fared well for construction activities when benchmarked relative to density, strength, and modulus of cores taken from constructed cement stabilized pavement layers. The PM Device was recommended for implementation consideration by state DOTs and other agencies.

Molecular dynamics simulations using the Embedded Atom Method were performed to describe the interparticle behavior of two single crystal spherical nickel nanoparticles during compaction based on applied strain rate, particle size, contact angle, and crystal orientation. The evolution of the contact surfaces was analyzed during the molecular dynamics simulation and an investigation of friction effects was conducted at the contact surfaces. The results from the current study were validated by comparing them to previous nanocrystalline research on bulk particle deformation and to previous studies of elasto-plastic contact laws between two macroscale spherical particles. These quantified friction effects give a better understanding of nanoparticle behavior and will be used to develop constitutive equations for larger scale models, such as finite element analysis.

Asphalt concrete pavements on commercial airports in the United States are constructed according to the Federal Aviation Administration Advisory Circular 150/5370-10B, Item P-401, “Plant Mix Bituminous Pavements.” This specification does not provide guidance for using the Superpave gyratory compactor in the design of asphalt mixtures. This thesis describes a laboratory study of hot mix asphalt (HMA) mix design for airport pavements that uses the Superpave gyratory compactor. These recommendations are based on comparisons of volumetric property measurements of HMA mixtures compacted using Marshall compaction and Superpave gyratory compaction.

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This work was performed under a cooporative research effort sponsored by the National Aeronautics and Space Administration (NASA) in conjunction with the aerospace industry and acedemia. One of the primary goals of NASA is to improve the safety and affordability of commercial air flight. Part of this goal includes research to reduce fuel consumption by developing lightweight carbon fiber, polymer matrix composites to replace existing metallic airframe structure. In the Twenty-first Aircraft Technology Program (TCAT) efforts were focused on developing novel processing methods to fabricate tailored composite airframe structure. The Vacuum Assisted Resin Transfer Molding (VARTM) processing technique offers a safer, more affordable alternative to manufacture large scale composite fuselages and wing structures. Vacuum assisted resin transfer molding is an infusion process originally developed for manufacturing of composites in the marine industry. The process is a variation of Resin Transfer Molding (RTM), where the rigid matched metal tooling is replaced on one side with a flexible vacuum bag. The entire process, including infusion and consolidation of the part, occurs at atmospheric pressure (101.5 kPa). High-performance composites with fiber volumes in the range of 45% to 50% can be achieved without the use of an autoclave. The main focus of the VARTM process development effort was to determine the feasibility of manufacturing aerospace quality composites with fiber volume fractions approaching 60%. A science-based approach was taken, utilizing finite element process models to characterize and develop a full understanding of the VARTM infusion process as well as the interaction of the constituent materials. Achieving aerospace quality composites requires further development not only of the VARTM process, but also of the matrix resins and fiber preforms. The present work includes an investigation of recently developed epoxy matrix resins, including the characterization of the resin cure kinetics and flow behaviors. Two different fiber preform architectures were characterized to determine the response to compaction under VARTM conditions including a study to determine the effect of thickness on maximum achievable fiber volume fraction. Experiments were also conducted to determine the permeabilities of these preforms under VARTM flow conditions. Both the compaction response and the permeabilities of the preforms were fit to empirical models which can be used as input for future work to simulate VARTM infusion using process models. Actual infusion experiments of these two types preforms were conducted using instrumented tools to determine the pressures and displacements that occur during VARTM infiltration. Flow experiments on glass tooling determined the fill-times and flow front evolution of preform specimens of various thicknesses. The results of these experiments can be used as validation of process model infusion simulations and to verify the compaction and permeability empirical models. Panels were infused with newly developed epoxy resins, cured and sectioned to determine final fiber volume fractions and part quality in an effort to verify both the infusion and compaction experimental data. The preforms characterized were found to have both elastic and inelastic compression response. The maximum fiber volume fraction of the knitted fabrics was dependent on the amount of stacks in the preform specimen. This relationship was found in the determination of the Darcy permeabilities of the preforms. The results of the characterization of the two epoxy resin systems the show that the two resins have similar minimum viscosities but significantly different curing behaviors. Characterization of the VARTM process resulted in different infusion responses in the two preform specimens investigated. The response of the saturated preform to a recompaction after infusion indicated that a significant portion of the fiber volume lost during infusion could be recovered. Fiber volume and void-content analysis of flat composite panels fabricated in VARTM using the characterized resins and preforms resulted in void-free parts with fiber volumes over 58%. Results in the idealized compaction tests indicated fiber volumes as high as 60% were achievable with the knitted fabric. The work over the presented here has led to a more complete understanding of the VARTM process but also led to more questions concerning its feasibility as an aerospace composite manufacturing technique. / Master of Science

Although many efforts and strategies have been implemented to reduce over-pumping of aquifer-systems, land subsidence is still a serious issue worldwide. Accurate aquifer characterization is critical to understand the response of an aquifer-system to prolonged pumping but is often difficult and expensive to conduct. The purpose of this thesis is to determine the validity of estimating aquifer-system parameters from a single cumulative compaction record and corresponding nested water-level data deconvolved into temporal components. Over a decade of compaction and water-level data were collected from an extensometer and multi-level piezometer at the Lorenzi site in Las Vegas Valley and when graphed yearly, seasonal, and daily signals are observed. Each temporal signal reflects different characteristics of the aquifer-system, including the distinction between aquifer and aquitard parameters, as the three temporal stresses influence the compaction record uniquely. Maximum cross-correlation was used to determine the hydrodynamic lag between changing water-levels and subsidence within the seasonal signal while principal components analysis was used to statistically verify the presence of the three temporal signals. Assumptions had to be made but nearly all estimated Lorenzi site aquifer-system parameters fell either within the reasonable range or were similar in magnitude to parameter values estimated in previous studies. Unfortunately, principal components analysis was unable to detect the three temporal signals. A cumulative compaction record may be difficult to obtain but analyzing the precision measurements of an extensometer results in precise aquifer-system parameters and as the precision of aquifer-system parameters increase so does the ability to sustainably manage groundwater. / Master of Science

The braided composite actuator is a pressure-driven muscle-like actuator capable of large displacements as well as large blocking forces. It consists of an elastomeric tube reinforced by a sleeve braided by high performance fibers. In addition to the actuation properties, this actuator can also exhibit a large change in stiffness through simple valve control when the working fluid has a high bulk modulus. Several analytical models have been previously developed that capture the geometrical and material nonlinearities, the compliance of the inner liner, and entrapped air in the fluid. The inter fiber yarn compaction in the fiber layer, which is shown to reduce the effective closed-valve stiffness, is studied. A new analytical model for uniformly deformed actuators is developed to capture the compaction effect. This model considers the inter fiber yarn compaction effect and the fiber extensibility as well as the material and geometric nonlinearities. Analysis and experimental results demonstrate that the new compaction model can improve the prediction of the response behavior of the actuator. The compaction model is improved by considering the yarn bending stiffness. The governing equations are derived and the solution algorithm is presented. / Ph. D.

Gutowski et al.'s model has been employed to describe the cure and consolidation of prepregs used for resin film infusion. Resin kinetics, rheology, flow and fiber deformation are considered. Resin kinetics are simulated with an isothermal autocatalytic-1 type relation. The non-Newtonian viscosity of the Cytec™ 754 resin is represented with a gel type expression. The one dimensional flow of resin through a deformable, partially saturated porous medium is studied. A nonlinear partial differential equation describing the spatial and temporal variation of the fiber volume fraction combining the continuity equation, Darcy's Law, and mat compressibility has been derived and solved numerically. Resin is assumed to be incompressible and inertial effects are neglected. Based on the resin content of regions where resin and fiber coexist, expressions for tracking resin flow through fully and partially saturated regions of fiber are given. Values of material parameters for the E-QX 3600-5 glass fabric are estimated from literature data involving compression of similar dry fabrics and through comparison of computed results with the experimental data. Results for the final thickness of the consolidated part agree with the experimental values, but those for the mass loss do not. / Master of Science