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Yes / The presence of cracks has a negative impact on the durability of concrete by providing paths for corrosive materials to the embedded steel reinforcement. Cracks in concrete can be closed using shape memory polymers (SMP) which produce a compressive stress across the crack faces. This stress has been previously found to enhance the load recovery associated with autogenous selfhealing. This paper details the experiments undertaken to incorporate SMP tendons containing polyethylene terephthalate (PET) filaments into reinforced and unreinforced 500 × 100 × 100 mm structural concrete beam samples. These tendons are activated via an electrical supply using a nickelchrome resistance wire heating system. The set-up, methodology and results of restrained shrinkage stress and crack closure experiments are explained. Crack closure of up to 85% in unreinforced beams and 26%–39% in reinforced beams is measured using crack-mouth opening displacement, microscope and digital image correlation equipment. Conclusions are made as to the effectiveness of the system and its potential for application within industry. / EPSRC for their funding of the Materials for Life (M4L) project (EP/K026631/1) and Costain Group PLC for industrial sponsorship of the project and author

Typically, foundation piles are made of materials such as steel, concrete, and timber. Problems associated with use of these traditional pile materials in harsh marine environments include steel corrosion, concrete deterioration, and marine borer attack on timber piles. It has been estimated that the U.S. spends over $1 billion annually in repair and replacement of waterfront piling systems. Such high repair and replacement costs have led several North American highway agencies and researchers to investigate the feasibility of using composite piles for load bearing applications, such as bridge substructures. As used here, the term "composite piles" refers to alternative pile types composed of fiber reinforced polymers (FRPs), recycled plastics, or hybrid materials. Composite piles may exhibit longer service lives and improved durability in harsh marine environments, thereby presenting the potential for substantially reduced total costs. Composite piles have been available in the North American market since the late 1980's, but have not yet gained wide acceptance in civil engineering practice. Potential disadvantages of composite piles are high initial cost and questions about engineering performance. At present, the initial cost of composite piles is generally greater than the initial cost of traditional piles. Performance questions relate to driving efficiency, axial stiffness, bending stiffness, durability, and surface friction. These questions exist because there is not a long-term track record of composite pile use and there is a scarcity of well-documented field tests on composite piles. This research project was undertaken to investigate the engineering performance of composite piles as load-bearing foundation elements, specifically in bridge support applications. The objectives of this research are to: (1) evaluate the soil-pile interface behavior of five composite piles and two conventional piles, (2) evaluate the long-term durability of concrete-filled FRP composite piles, (3) evaluate the driveability and the axial and lateral load behavior of concrete-filled FRP composite piles, steel-reinforced recycled plastic composite piles, and prestressed concrete piles through field tests and analyses, and (4) design and implement a long-term monitoring program for composite and conventional prestressed concrete piles supporting a bridge at the Route 351 crossing of the Hampton River in Virginia. A summary of the main findings corresponding to each of these objectives is provided below. A laboratory program of interface testing was performed using two types of sands and seven pile surfaces (five composite piles and two conventional piles). The interface behavior of the different pile surfaces was studied within a geotribology framework that investigated the influence of surface topography, interface hardness, and particle size and shape. In general, the interface friction angles, both peak and residual, were found to increase with increasing relative asperity height and decreasing relative asperity spacing. The interface shear tests for the three pile types tested at the Route 351 bridge showed that, for medium dense, subrounded to rounded sand, with a mean particle size of 0.5 mm, the residual interface friction angles are 27.3, 24.9, and 27.7 degrees for the FRP composite pile, the recycled plastic pile, and the prestressed concrete pile, respectively. Interface shear tests on these same piles using a medium dense, subangular to angular sand, with a mean particle size of 0.18 mm, resulted in residual interface friction angles of 29.3, 28.8, and 28.0 degrees for the FRP composite pile, the recycled plastic pile, and the prestressed concrete pile, respectively. A laboratory durability study was completed for the FRP shells of concrete-filled FRP composite piles. Moisture absorption at room temperature caused strength and stiffness degradations of up to 25% in the FRP tubes. Exposure to freeze-thaw cycles was found to have little effect on the longitudinal tensile properties of saturated FRP tubes. Analyses were performed to investigate the impact of degradation of the FRP mechanical properties on the long-term structural capacity of concrete-filled FRP composite piles in compression and bending. The impact was found to be small for the axial pile capacity due to the fact that the majority of the capacity contribution is from the concrete infill. The impact of FRP degradation was found to be more significant for the flexural capacity because the FRP shell provides most of the capacity contribution on the tension side of the pile. Full-scale field performance data was obtained for two composite pile types (concretefilled FRP composite piling and steel-reinforced recycled plastic piling), as well as for conventional prestressed concrete piles, by means of load test programs performed at two bridge construction sites: the Route 351 bridge and the Route 40 bridge crossing the Nottoway River in Virginia. The field testing at the two bridges showed no major differences in driving behavior between the composite piles and conventional prestressed concrete piles. Pile axial capacities of the composite piles tested at the Route 351 bridge were between 70 to 75% of the axial capacity of the prestressed concrete test pile. The FRP and prestressed concrete piles exhibited similar axial and lateral stiffness, while the steel-reinforced plastic pile was not as stiff. Conventional geotechnical analysis procedures were used to predict axial pile capacity, axial load-settlement behavior, and lateral load behavior of the piles tested at the Route 351 bridge. The conventional analysis procedures were found to provide reasonable predictions for the composite piles, or at least to levels of accuracy similar to analyses for the prestressed concrete pile. However, additional case histories are recommended to corroborate and extend this conclusion to other composite pile types and to different soil conditions. A long-term monitoring program for composite and conventional prestressed concrete piles supporting the Route 351 bridge was designed and implemented. The bridge is still under construction at the time of this report, therefore no conclusions have been drawn regarding the long-term performance of concrete-filled FRP composite piles. The longterm monitoring will be done by the Virginia Department of Transportation. In addition to the above findings, initial cost data for the composite piles and prestressed concrete piles used in this research were compiled. This data may be useful to assess the economic competitiveness of composite piles. The initial unit cost of the installed composite piles at the Route 40 bridge were about 77 % higher than the initial unit cost for the prestressed concrete piles. The initial unit costs for the composite piles installed at the Route 351 bridge were higher than the initial unit cost of the prestressed concrete piles by about 289% and 337% for the plastic and FRP piles, respectively. The cost effectiveness of composite piles is expected to improve with economies of scale as production volumes increase, and by considering the life-cycle costs of low-maintenance composite piles. / Ph. D.

As fiber reinforced polymer matrix composites find greater use in markets such as civil infrastructure and ground transportation, the expectations placed on these materials are ever increasing. The overall cost and reliability have become the drivers of these high performance materials and have led to the disappearance of resins such as bismaleimides (BMI), cyanate esters and other high performance polyimides and epoxys. In their place polymers, such polyester and vinylester have arisen. The reinforcing fiber scenario has also undergone changes from the high quality and performance assured IM7 and AS4 to cheaper and hybrid systems consisting of both glass and low cost carbon. Manufacturing processes have had their share of changes too with processes such as pultrusion and other mass production techniques replacing hand lay-up and resin transfer molding. All of this has however come with little or no concession on material performance. The motivation of the present research has therefore been to try to improve the properties of these low cost composites by better understanding the constituent materials (fiber and matrix) and the region that lies in-between them namely the interphase. In order to achieve this, working with controls is necessary and the present discourse therefore deals with the AS4 fiber system from Hexcel Corporation and the vinyl ester resin, Derakane 441-400 from The Dow Chemical Company. The following eight chapters sum up the work done thus far on composites made with sized fibers and the above mentioned resin and fiber systems. They are in the form of publications that have either been accepted, submitted or going to be submitted to various peer reviewed journals. The sizings used have been poly(vinylpyrrolidone) PVP and Polyhydroxyether (Phenoxy) thermoplastic polymers and G' an industrial sizing material supplied by Hexcel. A number of issues have been addressed ranging from viscoelastic relaxation to enviro-mechanical durability. Chapter 1 deals with the influence of the sizing material on the fatigue response of cross ply composites made with the help of resin infusion molding. Chapter 2 describes the effects of a controlled set of interphase polymers that have the same chemical structure but differ from each other in polarity. The importance of the atomic force microscope (AFM) to view and perform nano-indentations on the interphase regions has been demonstrated. Finally, it attempts to tie everything together with the help of the fatigue response of the different composites. Chapter 3 deals only with the vinyl ester resin and examines the influence of network structure on the molecular relaxation behavior (cooperativity) of the glassy polymer. It also tries to make connections between structural features of the glass and fracture toughness as measured in its glassy state. Chapter 4 extends the results obtained in chapter 3 to examine the cooperativity of pultruded composites made with the different sizings. A correlation between strength and cooperativity is found to exist, with systems having greater cooperativity being stronger. Chapter 5 moves into the area of hygrothermal aging of Derakane 441-400 resin. It looks specifically at identifying a mechanism for the unusual moisture uptake behavior of the polymer subjected to a thermal-spiking environment. This it does by identifying the presence of hydrogen bonding in the resin. Finally, chapters 6 to 8 present experimental and analytical results obtained on PVP K90, Phenoxy and G' sized, AS4/Derakane 411-350 LI vinyl ester composites that were pultruded at Strongwell Inc., on their lab-scale pultruder in Bristol, Virginia. / Ph. D.

The use of water based adhesive primers in enhancing the durability of aluminum adhesively bonded with epoxy was studied. The effects of the thickness of both the aluminum oxide surface layer and the primer layer on bond durability were established. 5052 aluminum alloy was oxidized by phosphoric acid anodization prior to primer coating. The oxide layer thickness was controlled mainly by changing anodization voltage and directly measured using a HR-SEM (high resolution scanning electron microscope). The oxide layer was also examined by AES (Auger electron spectroscopy) and XPS (X ray photoelectron spectroscopy). The surface oxide layer was porous and the thickness varied from 0.2 to 2.2 μm. The anodized aluminum substrates contained 3 atomic % of phosphorus and were coated with several solid concentrations of water based adhesive primers. These primers contained non-reactive polyurethane emulsions, and were dried at room temperature. The primer thicknesses were measured by ellipsometry. The primer penetrated into the aluminum oxide pores, confirmed by observing the primer surface after the aluminum oxide was removed by dissolving in dilute NaOH aqueous solution. All adhesive bonding was done using the wedge test configuration with a structural epoxy adhesive, Naviloc® XY 0210, which was cured for 30 min. at 180°C. The wedge samples were immersed in 80°C water and crack lengths were monitored as a function of time. Both the initial crack length and crack propagation were minimized when the primer thickness was a little less than the aluminum oxide thickness. In a separate study, the aluminum oxide surfaces were aged in hot water or hot humid environment before bonding. The crack lengths of the aged samples for both 60°C water immersion and 70°C ≥95 %R.H. conditions were similar to those of non-aged sample. On the other hand, when the samples were aged in 80°C water, the oxide was hydrated and the crack length increased. The locus of failure also changed from cohesive failure in the adhesive for the lower temperature aged samples to a mixed mode of cohesive failure and aluminum oxide-primer interfacial failure for the 80°C aged samples. / Master of Science

The purpose of this study was to evaluate the physical properties of dental sealant resins under aging conditions to determine the critical factors controlling functional property loss with time. The effect of processing on the chemical and thermal properties of several different sealant formulations was evaluated. These processing parameters included the blue light exposure time for each light-curing system and time after illumination. The results indicate that the level of cure for each system was incomplete at the end of all processing procedures. Heating as well as further aging of the cured resin advanced the cure. Additionally, one of our goal was to model the curing characteristics of the sealant as a function of depth in the fissure to evaluate the thickness influence on the sealant mechanical properties. The strength and stiffness of the light-cured sealant varied as a function of depth in the fissure. This results in a gradient of deformation which could cause early fracture of the resin upon chewing. Incomplete resin conversion is important since dental adhesives have been shown to be leached by saliva and the elution products have been recently shown to be potentially estrogenic. Samples of differently processed commercial sealants were immersed in an ethanol/water solution and extractions were analyzed by HPLC. An inverse correlation between the degree of cure and the % of elution as well as high level of extraction was found. An <i>in vivo</i> study has been performed on fifteen pigs. The purpose of the experiment is to obtain data on <i>in vivo</i> sealing ability of the sealant. Low sealant retention rates have been found but interesting observations of sealed fissures were made and the pig can be considered like an acceptable model. / Master of Science

The effect of cyclic moisture infiltration on connections in light-frame wood buildings has received limited research attention. Specifically, the connections between wood-based sheathing materials (OSB, plywood) and solid wood studs are of interest. A comprehensive understanding of connection performance will enhance structure and material design, thereby improving the overall integrity and robustness of light-frame structures. The focus of this research project was to evaluate the strength and stiffness of wood-frame connections exposed to cyclic humidity conditioning. Nailed sheathing/stud connection samples were tested for lateral resistance following various periods of moisture exposure. Elastic stiffness, 5% offset yield load, maximum yield load, and failure yield were computed and analyzed using the data collected. The parameters were compared among connection specimens receiving either 0, 1, 5, 10, 15, 25, or 40 periods of cyclic moisture conditioning. In addition, the bearing resistances of the materials were investigated for application to the general dowel equations for calculating lateral connection values, the current basis for design of single dowel-type fastener connections between wood-based members. An x-ray density profilometer was used to observe the de-densification processes within the composite sheathing materials throughout the moisture conditioning regime. Results indicated moderate to extreme changes in the performance of cycled connections involving lower density sheathing materials. Higher density sheathing materials performed favorably at each cycle test period. Comparisons to the yield model were similar to the control results, but usually differed as cycling increased. Analysis of connection performance following cyclic moisture loading is a vital component in developing a holistic model for service-life prediction of nailed connections in light-frame residential construction. / Master of Science

The bond performance and surface energy of hygro-thermal compression densified wood were studied using comparisons to hygro-thermally treated and control yellow-poplar (Liriodendron tulipifera). Bond performance was studied using opening mode double cantilever beam fracture testing and cyclic boiling of one half of all fracture samples. Phenol formaldehyde film (PF-film) and polymeric diphenylmethane diisocyanate (pMDI) were the two different adhesives used to bond fracture samples. Hygro-thermal samples bonded with PF-film had significantly higher fracture toughness than control samples, while no difference was found for densified samples. Densified samples bonded with pMDI had significantly higher fracture toughness than control samples while no change was seen for hygro-thermal samples. Boil cycling reduced fracture toughness of hygro-thermal fracture samples only, irrespective of adhesive type. Surface energy was studied using sessile drop contact angle measurement and the Chang model of acid-base, surface energy component calculation. Water, glycerol, formamide, ethylene glycol, and &#61537;-Bromonapthalene were used as probe liquids. Densified and hygro-thermally treated yellow-poplar had significantly higher contact angles than control samples. The contact angle trends for densified and hygro-thermally treated wood were found to be the same. Total surface energy as well as the polar and acid components of surface energy decreased with hygro-thermal treatment. The dispersive and base components of surface energy increased with hygro-thermal treatment. / Master of Science