Browsing by Author "Weyers, Richard E."

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    Analytical modeling of hybrid composite beams
    Bhutta, Salman Ahmed (Virginia Tech, 1993-12-06)
    The main objective of this study is to develop an analytical model to explain the behavior of a hybrid structure under different loading conditions. The model developed for a simply supported beam on moment capacity, stiffness, and deflection can be generalized to deal with any type of material combination. The dependence of moment capacity of the hybrid beam on the thickness of the composite sheet was investigated. The inherent property of a high Young's modulus and strain-to-failure properties of the composite material increased the moment capacity of the RC beam dramatically. The moment model showed a percentage increase of 284% for KFRP while on the other hand the percentage increases for CFRP and GFRP were 191% and 174% respectively when using a FRP sheet of thickness 0.025 mm. KFRP showed the highest increase in moment capacity because of its high strain-to-failure. CFRP on the other hand has a high Young's modulus, but its strain to failure is low, causing it to lie in the middle range. The analytical model is that the ability of a beam to handle moment is strongly dependent on the strength characteristics and the thickness of the FRP sheet.
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    Assessment of Commercial Corrosion Inhibiting Admixtures for Reinforced Concrete
    Brown, Michael Carey (Virginia Tech, 1999-11-11)
    Corrosion of reinforcing steel in concrete exposed to chloride-laden environments is a well-known and documented phenomenon. The need for cost effective systems for protection against corrosion has become increasingly clear since the first observations of severe corrosion damage to interstate bridges in the 1960's. As one potential solution to the mounting problem of corrosion deterioration of structures, corrosion-inhibiting admixtures have been researched and introduced into service. This report conveys the results of a three-part laboratory study of corrosion inhibiting admixtures in concrete. The commercial corrosion inhibiting admixtures for concrete have been analyzed by three evaluation methods, including: • Conventional concrete corrosion cell prisms under ponding, • Black steel reinforcing bars immersed in simulated concrete pore solutions, • Electrochemical screening tests of special carbon steel specimens in electrochemical corrosion cells containing filtered cement slurry solution. The purposes of the study include: • Determining the influence of a series of commercially available corrosion inhibiting admixtures on general concrete handling, performance and durability properties not related to corrosion. • Determining the effectiveness of corrosion inhibiting admixtures for reduction or prevention of corrosion of reinforcing steel in concrete, relative to untreated systems, under laboratory conditions. • Conducting a short-term pore solution immersion test for inhibitor performance and relating the results to those of the more conventional long-term corrosion monitoring techniques that employ admixtures in reinforced concrete prisms. • Determining whether instantaneous electrochemical techniques can be applied in screening potential inhibitor admixtures. Concrete properties under test included air content, slump, heat of hydration, compressive strength, and electrical indication of chloride permeability. Monitoring of concrete prism specimens included macro-cell corrosion current, mixed-cell corrosion activity as indicated by linear polarization, and ancillary temperature, relative humidity, and chloride concentration documentation. Simulated pore solution specimens were analyzed on the basis of weight loss and surface area corroded as a function of chloride exposure. Electrochemical screening involved polarization resistance of steel in solution. Results include corrosion potential, polarization resistance and corrosion current density.
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    Assessment of Infrared Thermography for NDE of FRP Bridge Decks
    Miceli, Marybeth (Virginia Tech, 2000-12-11)
    Statistics released in the fall 1989 showed that 238,357 (41%) of the nation's 577,710 bridges are either structurally deficient or functionally obsolete. New materials, such as fiber reinforced polymeric composites (FRP), are being suggested for use in bridge systems to solve some of the current problems. These materials are thought to be less affected by corrosive environmental conditions than conventional civil engineering materials. Therefore they may require less maintenance and provide longer life spans. More specifically, glass fiber reinforced vinyl ester matrix composites are considered possible replacements for deteriorating conventional bridge decks due to their durability, decreased weight, and relative affordability. In order to facilitate rapid acceptance of FRP structural components into the world of civil structural engineering, effective and efficient NDE techniques must be explored and documented in these situations. This thesis will discuss the use of Infrared Thermography (IRT) as a means of detecting debonds and voids caused by conditions encountered both in fabrication and in the field. As forced convective hot air is applied within the bridge deck, debonds between bridge deck components near the riding surface appear cold while imperfections near the bottom of the deck give rise to concentrations of heat. These variations in thermal propagation patterns are observed by the infrared camera and indicate possible structural deficiencies. Results of experimentation and thermal analyses from laboratory studies of a model bridge deck and some from in situ full-scale investigations are presented.
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    Automated Characterization of Bridge Deck Distress Using Pattern Recognition Analysis of Ground Penetrating Radar Data
    Scott, Michael L. (Virginia Tech, 1999-08-02)
    Many problems are involved with inspecting and evaluating the condition of bridges in the United States. Concrete bridge deck inspection and evaluation presents one of the largest problems. The deterioration of these concrete decks progresses more rapidly than any other bridge component, which leads to early concrete deck replacements that must be done before the bridge superstructure needs to be replaced. The primary cause of deterioration in these concrete bridge decks is corrosion-induced concrete cracking, which frequently results in delaminations. Delamination distress increases the life cycle cost of maintaining a concrete bridge deck, particularly when it is not detected early on. Early detection of delamination distress can facilitate economical repair and rehabilitation work, but bridge engineers must recommend deck replacement if repairs are delayed too long or inspection tools cannot detect delaminations early enough. The Federal Highway Administration has responded to the need for a better bridge deck inspection tool by contracting Lawrence Livermore National Laboratory to develop two new prototype ground penetrating radar systems. These two systems generate three-dimensional data that provide a representation of features that lie below the bridge deck surface. Both of these systems produce large amounts of data for an individual bridge deck, which makes automated data processing very desirable. The primary goal of the automated processing is to characterize bridge deck distress represented in the data. This study presents data collected from sample bridge deck sections using one of the prototype systems. It also describes the development and implementation of appropriate methods for automating data processing. The automated data processing is accomplished using image processing and pattern recognition algorithms developed in the study.
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    Bridge Deck Service Life Prediction and Costs
    Williamson, Gregory; Weyers, Richard E.; Brown, Michael C.; Sprinkel, Michael M. (Virginia Center for Transportation Innovation and Research, 2007-12-01)
    The service life of Virginia's concrete bridge decks is generally controlled by chloride-induced corrosion of the reinforcing steel as a result of the application of winter maintenance deicing salts. A chloride corrosion model accounting for the variable input parameters using Monte Carlo resampling was developed. The model was validated using condition surveys from 10 Virginia bridge decks built with bare steel. The influence of changes in the construction specifications of w/c = 0.47 and 0.45 and w/cm = 0.45 and a cover depth increase from 2 to 2.75 inches was determined. Decks built under the specification of w/cm = 0.45 (using slag or fly ash) and a 2.75 inch cover depth have a maintenance free service life of greater than 100 years, regardless of the type of reinforcing steel. Galvanized, MMFX-2, and stainless steel, in order of increasing reliability of a service life of greater than 100 years, will provide a redundant corrosion protection system. Life cycle cost analyses were conducted for polymer concrete and portland cement based overlays as maintenance activities. The most economical alternative is dependent on individual structure conditions. The study developed a model and computer software that can be used to determine the time to first repair and rehabilitation of individual bridge decks taking into account the time for corrosion initiation, time from initiation to cracking, and time for corrosion damage to propagate to a state requiring repair.
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    Characterization and deterioration detection of Portland cement concrete using electromagnetic waves over a wideband of frequency
    Haddad, Rami H. (Virginia Tech, 1996-01-05)
    An experimental program was conducted to establish a better understanding of the effect of Portland cement concrete's (PCC' s) basic properties on its dielectric properties over a wideband of frequency (0.1 MHz-10 GHz). Other parameters that may influence measured dielectric properties were investigated. These include chlorides presence in PCC, deterioration (due to alkali silica reaction [ASR] and freezing and thawing [Fff] damage), delamination, and segregation. In addition, the effect of different sizes of delaminated areas (filled with water) was evaluated using measured dielectric properties and waveform amplitude. Three different electromagnetic wave (EM) setups were used to conduct those measurements: parallel plate capacitor (0.1-40 MHz), coaxial transmission line (100 MHz to 1 GHz), and TEM antenna (0.5-10 GHz). The setups were designed and built by engineers from the Civil and Electrical Engineering Departments at Virginia Tech as a part of the overall research study. Testing results indicated the feasibility of using EM to detect changes in the basic properties of PCC over low RF using the parallel plate capacitor. This included the effect of curing time, water to cement (w/c) ratio, aggregate type, cement type, and air entrainment. The effect of curing time on the complex dielectric constant of PCC was quantitatively determined. However, the success in detecting changes in the PCC basic properties was limited at the microwave frequency range of 100 MHz to 10 GHz. Changes in the complex dielectric constant due to chloride intrusion into PCC were quantitatively significant only over the low radio wave frequency. The ASR in PCC was successfully identified by measured complex dielectric constant over the low RF, especially less than 20 MHz. Insignificant changes in the complex dielectric constant over the frequency range of 0.1 MHz to 1 GHz was noted when PCC was exposed to FIT cycles. Complex dielectric constant and waveform amplitude measurements of pce slabs over frequency range of 1 to 10 GHz showed significant changes with water content (in PCC); due to further hydration or injecting of water into empty delaminated areas. Waveform amplitude showed significant sensitivity to delamination and chlorides and low sensitivity to segregation. After testing several mixture theories to identify the most appropriate theory that is capable of predicting the dielectric constant of PCC (based on the dielectric properties of its components), Bruggemenn mixture theory was found to be the most feasible.
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    Characterization and Modeling of a Fiber-Reinforced Polymeric Composite Structural Beam and Bridge Structure for Use in the Tom's Creek Bridge Rehabilitation Project
    Hayes, Michael David (Virginia Tech, 1998-12-12)
    Fiber reinforced polymeric (FRP) composite materials are beginning to find use in construction and infrastructure applications. Composite members may potentially provide more durable replacements for steel and concrete in primary and secondary bridge structures, but the experience with composites in these applications is minimal. Recently, however, a number of groups in the United States have constructed short-span traffic bridges utilizing FRP members. These demonstration cases will facilitate the development of design guidelines and durability data for FRP materials. The Tom's Creek Bridge rehabilitation is one such project that utilizes a hybrid FRP composite beam in an actual field application. This thesis details much of the experimental work conducted in conjunction with the Tom's Creek Bridge rehabilitation. All of the composite beams used in the rehabilitation were first proof tested in four-point bending. A mock-up of the bridge was then constructed in the laboratory using the actual FRP beams and timber decking. The mock-up was tested in several static loading schemes to evaluate the bridge response under HS20 loading. The lab testing indicated a deflection criterion of nearly L/200; the actual field structure was stiffer at L/450. This was attributed to the difference in boundary conditions for the girders and timber panels. Finally, the bridge response was verified with an analytical model that treats the bridge structure as a wood beam resting upon discrete elastic springs. The model permits both bending and torsional stiffness in the composite beams, as well as shear deformation. A parametric study was conducted utilizing this model and a mechanics of laminated beam theory to provide recommendations for alternate bridge designs and modified composite beam designs.
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    Chemical treatment of corroding steel reinforcement after removal of chloride contaminated concrete
    Collins, William D. (Virginia Tech, 1991-06-12)
    The increasing use of deicing salts has caused the accelerated deterioration of bridge decks due to cracking and spalling from chloride induced corrosion of steel reinforcement. One method being considered as a possible corrosion abatement measure is the removal of chloride contaminated concrete and the chemical treatment of the partially exposed rebar through ponding and/or placement of chemically treated mortar. Reinforced concrete specimens were cast and subjected to repeated exposure to NaCl solution. Half-cell potential, corrosion rate, and chloride ion concentration measurements were conducted until the indication of active reinforcement corrosion. Chloride contaminated concrete was removed to the rebar level through a grooving process. The grooves were chemically treated through solution pondings and backfilling with treated mortar. Seventeen treatments and combination of treatments were evaluated including corrosion inhibitors, polymer sealers, and a possible chloride ion scavenging mineral. The treatment effects were monitored using half-cell potential and corrosion rate measurements. In addition, mortar cubes were cast containing various treatment concentrations and were subsequently tested for compressive strength and change in resistivity over time. Based on the electrochemical and mortar cube measurements, DCI (calcium nitrite) when applied as a ponding and mortar treatment, was determined most effective in abating corrosion after concrete removal. In addition, Alox 901, Cortec 1337, Cortec 1609, sodium tetraborate, and Zinc borate were also found effective in mitigating rebar corrosion after concrete removal; however, both the borate compounds cause set retardation of portland cement. These chemicals were recommended as candidate treatments for further evaluation in both large-scale and field experimentation.
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    Comparison and Analysis of the Strength, Stiffness, and Damping Characteristics of Concrete with Rubber, Latex, and Carbonate Additives
    Bowland, Adam Gregory (Virginia Tech, 2011-06-27)
    This dissertation presents the results of a study performed to investigate methods for increasing the damping capacity of concrete. A variety of additives, both particle and latex based, were added to standard concrete mixtures by replacing up to 20% of the fine aggregate to measure their effects on strength, stiffness, damping, and air content. The additives included rubber particles from recycled tires, calcium carbonate particles, styrene butadiene rubber (SBR) latex, and a commercially available product named ConcreDamp which contains vegetable gum suspended in styrene butadiene latex. An initial investigation resulted in the observation that all of the additives with the exception of the SBR latex would both increase air content and decrease compressive strength. As a result, combinations of additives were investigated to see if both the mechanical and dynamic properties could be improved. The addition of steel fibers to mixtures with ground rubber were found to significantly increase air content which offset any gains in compressive strength. The combination of ground rubber and latex was shown to improve both increase compressive strength and reduce air content. The study advanced to investigate the effects of rubber size on air content, strength, and damping. It was found that for the same volume of rubber, a larger rubber particle would decrease air content, decrease compressive strength, and improve damping. The results of this study show that the best performing additive was the vegetable gum latex which improved the concrete damping by a factor of 2 when added as 15% of the fine aggregate. Additionally, an equation is presented for calculating a strength reduction factor for concrete containing rubber particles of different sizes. Finally, two full scale footbridge laboratory specimens were tested to investigate the effect of increased material damping at the structural level. One footbridge was constructed using a base concrete mixture without damping admixtures. The second was constructed with a concrete mixture that contained a replacement of 15% of the fine aggregate with ground rubber. The results were used to create a finite element model in SAP2000 that was used to predict the effects that high damping concretes would have on the footbridge specimen.
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    Compressive Creep of a Lightweight, High Strength Concrete Mixture
    Vincent, Edward Creed (Virginia Tech, 2003-01-10)
    Concrete undergoes volumetric changes throughout its service life. These changes are a result of applied loads and shrinkage. Applied loads result in an instantaneous recoverable elastic deformation and a slow, time dependent, inelastic deformation called creep. Creep without moisture loss is referred to as basic creep and with moisture loss is referred to as drying creep. Shrinkage is the combination of autogeneous, drying, and carbonation shrinkage. The combination of creep, shrinkage, and elastic deformation is referred to as total strain. The prestressed concrete beams in the Chickahominy River Bridge have been fabricated with a lightweight, high strength concrete mixture (LTHSC). Laboratory test specimens have been cast using the concrete materials and mixture proportions used in the fabrication of the bridge beams. Two standard cure and two match cure batches have been loaded for 329 and 251 days, respectively. Prestress losses are generally calculated with the total strain predicted by the American Concrete Institute Committee 209 recommendations, ACI 209, or the European design code, CEB Model Code 90. Two additional models that have been proposed are the B3 model by Bazant and Baweja, and the GL2000 model proposed by Gardner and Lockman. The four models are analyzed to determine the most precise model for the LTHSC mixture. Only ACI 209 considered lightweight aggregates during model development. GL2000 considers aggregate stiffness in the model. ACI 209 was the best predictor of total strain and individual time dependent deformations for the accelerated cure specimens. CEB Mode Code 90 was the best predictor of total strain for the standard cure specimens. The best overall predictor of time dependent deformations was the GL2000 model for the standard cure specimens.
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    Compressive Creep of Prestressed Concrete Mixtures With and Without Mineral Admixtures
    Meyerson, Richard (Virginia Tech, 2001-02-16)
    Concrete experiences volume changes throughout its service life. When loaded, concrete experiences an instantaneous recoverable elastic deformation and a slow inelastic deformation called creep. Creep of concrete is composed of two components, basic creep, or deformation under load without moisture loss and drying creep, or deformation under drying conditions only. Deformation of concrete in the absence of applied load is often called shrinkage. The deformation due to creep is attributed to the movement of water between the different phases of the concrete. When an external load is applied, it changes the attraction forces between the cement gel particles. This change in the forces causes an imbalance in the attractive and disjoining forces. However, the imbalance is gradually eliminated by the transfer of moisture into the pores in cases of compression, and away from the pores in cases of tension. Designs typically use one of the two code models to estimate creep and shrinkage strain in concrete, ACI 209 model recommended by the American Concrete Institute or the CEB 90 Eurocode 2 model recommended by the Euro-International Committee. The ASSHTO LRFD is based on the ACI 209 model. Three other models are the B3 model, developed by Bazant; the GZ model, developed by Gardner; and the SAK model developed by Sakata. The development of concrete performance specifications that limit the amount of compressive creep of concrete mixtures used by the Virginia Department of Transportation, specifically concrete mixtures used for prestressed members (A-5 Concrete) were assessed, along with determining the accuracy and precision of the creep models presented in the literature. The CEB 90 Eurocode 2 model for creep and shrinkage is the most precise and accurate predictor. The total strain for the VDOT portland cement concrete mixtures discussed in this study were found to be between 1200 ± 110 microstrain at 28 days, and 1600 ± 110 microstrain at 97 days, at a five percent significant level.
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    Correlation of corrosion measurements and bridge conditions with NBIS deck rating
    Ramniceanu, Andrei (Virginia Tech, 2004-10-11)
    Since the use of epoxy coated steel has become mandatory starting in the 1980s, recent studies have shown that epoxy coating does not prevent corrosion, but instead will debond from the steel reinforcement in as little as 4 years (Weyers RE et al, 1998) allowing instead a much more insidious form of corrosion to take place known as crevice corrosion. Therefore, it is important to determine if the nondestructive corrosion activity detection methods are applicable to ECR as well as institute guidelines for interpreting the results. Since the corrosion of reinforcing steel is directly responsible for damage to concrete structures, it is surprising that nondestructive corrosion assessment methods are not part of regular bridge inspection programs such as PONTIS and NBIS. Instead, the inspection and bridge rating guidelines of federally mandated programs such as NBIS are so vague as to allow for a relatively subjective application by the field inspectors. Clear cover depths, resistance, corrosion potentials, linear polarization data, as well as environmental exposure and structural data were collected from a sample of 38 bridge decks in the Commonwealth of Virginia. These structures were further divided in three subsets: bridge decks with a specified w/c ratio of 0.47, bridge decks with a specified w/c ratio of 0.45 and bridge decks with a specified w/cm ratio of 0.45. This data was then correlated to determine which parameters are the most influential in the assignment of NBIS condition rating. Relationships between the non-destructive test parameters were also examined to determine if corrosion potentials and linear polarization are applicable to epoxy coated steel. Based on comparisons of measurements distributions, there is an indication that corrosion potential tests may be applicable to structures reinforced with epoxy coated steel. Furthermore, these conclusions are supported by statistical correlations between resistivity, half cell potentials and linear polarization measurements. Unfortunately, although apparently applicable, as of now there are no guidelines to interpret the results. Based on the linear corrosion current density data collected, no conclusion can be drawn regarding the applicability of the linear polarization test. As far as the NBIS deck rating is concerned, since the inspection guidelines are so vague, age becomes a very easy and attractive factor to the field personnel to rely on. However, this conclusion is far from definitive since the very large majority of structures used in this particular study had only two rating values out of theoretically ten and realistically five possible rating values.
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    Corrosion Assessment for Failed Bridge Deck Closure Pour
    Abbas, Ebrahim K. (Virginia Tech, 2011-12-02)
    Corrosion of reinforcing steel in concrete is a significant problem around the world. In the United States, there are approximately 600,000 bridges. From those bridges 24% are considered structurally deficient or functionally obsolete based on the latest, December 2010, statistic from the Federal Highway Administration (FHWA). Mainly, this is due to chloride attack present in deicing salts which causes the reinforcing steel to corrode. Different solutions have been developed and used in practice to delay and prevent corrosion initiation. The purpose of this research is to investigate the influence of corrosion on the failure mechanism that occurred on an Interstate 81 bridge deck. After 17 years in service, a 3ft x3ft closure pour section punched through. It was part of the left wheel path of the south bound right lane of the bridge deck. The bridge deck was replaced in 1992 as part of a bridge rehabilitation project, epoxy coated reinforcement were used as the reinforcing steel. Four slabs from the bridge deck, containing the closure, were removed and transported to the Virginia Tech Structures and Materials Research Laboratory for further evaluation. Also, three lab cast slabs were fabricated as part of the assessment program. Corrosion evaluation and concrete shrinkage characterization were conducted in this research. The corrosion evaluation study included visual observation, clear concrete cover depth, concrete resistivity using single point resistivity, half-cell potential, and linear polarization using the 3LP device. Shrinkage characteristics were conducted on the lab cast slabs only, which consisted of monitoring shrinkage behavior of the specimens for 180 days and comparison of the data with five different shrinkage models. Based on the research results, guidance for assessment of other bridge decks with similar conditions will be constructed to avoid similar types of failures in the future.
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    Corrosion inhibiting repair and rehabilitation treatment process for reinforced concrete structures
    (United States Patent and Trademark Office, 1995-06-27)
    A repair and rehabilitation treatment process for reinforced concrete structures involves the removal of concrete from above rebar or other metal reinforcement material in the concrete structure. After removal of concrete, the metal reinforcement materials are saturated with corrosion inhibiting agents. Saturation is best achieved by multiple spray applications of the corrosion inhibitor. The cavity in the concrete structure with the treated rebar or other metal reinforcement materials is then backfilled and/or overlaid with repair concrete. Preferably, the repair concrete includes corrosion inhibitors which will diffuse to the rebar over time or is a low permeability concrete that reduces the rate of diffusion of chloride corrosion causing agents to the rebar. The repair and rehabilitation process significantly increases the concrete structure's service life.
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    Corrosion Protection Service Life of Epoxy Coated Reinforcing Steel in Virginia Bridge Decks
    Brown, Michael Carey (Virginia Tech, 2002-05-03)
    The corrosion protection service life extension provided by epoxy-coated reinforcement (ECR) was determined by comparing ECR and bare bar from 10 bridge decks built between 1981 and 1995. The objective was to determine the corrosion protection service life time extension provided by ECR field specimens with various degrees of coating adhesion: disbonded, partially disbonded, and wholly bonded coatings. The size and length distributions of cracks in Virginia bridge decks were investigated to assess the frequency and severity of cracks. Correlation of cracks with chloride penetration was used to characterize the influence of cracking on deck deterioration. Cracks influence the rate of chloride penetration, but the frequency and width distributions of cracks indicate that cracks are not likely to shorten the overall service life of most bridge decks in Virginia. Altogether, 141 drilled cores, 102 mm (4 inches) in diameter, were employed in this study. For each of the decks built with ECR, 10 to 12 cores were drilled through a top reinforcing bar adjacent to the previous study core locations. In addition, approximately 3 cores were drilled through a top reinforcing bar at a surface crack location. Laboratory testing involved nondestructive monitoring using advanced electrochemical techniques to periodically assess the corrosion state of the steel bars during cyclic exposure to chloride-rich solution over 22 months of treatment. Time of corrosion initiation and time of cracking (where applicable), as well as chloride content of the concrete before and after treatment, were used in the analysis. Less than 25 percent of all Virginia bridge decks built under specifications in place since 1981 is projected to corrode sufficiently to require rehabilitation within 100 years, regardless of bar type. The corrosion service life extension attributable to ECR in bridge decks was found to be approximately 5 years beyond that of bare steel.
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    Corrosion Protection Service Life of Epoxy-Coated Reinforcing Steel in Virginia Bridge Decks
    Brown, Michael C.; Weyers, Richard E.; Megan C. Wheeler (Virginia Center for Transportation Innovation and Research, 2003-09-01)
    The corrosion protection service life extension provided by epoxy-coated reinforcement (ECR) was determined by comparing ECR and bare steel bars from 10 Virginia bridge decks built between 1981 and 1995. The objective was to determine the corrosion protection service life time extension provided by ECR field specimens with various degrees of coating adhesion: disbonded, partially disbonded, and wholly bonded coatings. The size and length distributions of cracks in Virginia bridge decks were investigated to assess the frequency and severity of cracks. Correlation of cracks with chloride penetration was used to characterize the influence of cracking on deck deterioration. Cracks influence the rate of chloride penetration, but the frequency and width distributions of cracks indicate that cracks are not likely to shorten the overall service life of most bridge decks in Virginia. Altogether, 141 drilled cores, 102 mm (4 inches) in diameter, were employed in this study. For each of the decks built with ECR, 10 to 12 cores were drilled through a top reinforcing bar adjacent to the previous study core locations. In addition, approximately 3 cores were drilled through a top reinforcing bar at a surface crack location. Laboratory testing involved nondestructive monitoring using advanced electrochemical techniques to periodically assess the corrosion state of the steel bars during cyclic exposure to chloride-rich solution over 36 months of treatment. Time of corrosion initiation and time of cracking (where applicable), as well as chloride content of the concrete before and after treatment, were used in the analysis. Analysis of the epoxy coating after treatment showed the presence of micro cracks in the surface of some coatings, and moisture uptake and glass transition temperatures, as related to curing of the coatings, were investigated. Less than 25 percent of all Virginia bridge decks built under specifications in place since 1981 is projected to corrode sufficiently to require rehabilitation within 100 years, regardless of bar type. The corrosion service life extension attributable to ECR in bridge decks was found to be approximately 5 years beyond that of bare steel and, therefore, ECR is not a cost-effective method of corrosion prevention for bridge decks. Deleting the requirement for ECR in decks would save Virginia approximately $845,000 per year.
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    Corrosion Testing and Modeling of Chloride-Induced Corrosion Deterioration of Concrete Bridge Decks
    Govindarajan Balakumaran, Soundar Sriram (Virginia Tech, 2012-03-01)
    Modeling of chloride-induced deterioration of bridge decks by using Fick's Second Law of diffusion was performed. The objective of this study is to select suitable input parameters for the model to estimate the service life of bridge decks. Five bridge decks, one in each of the following states, Virginia, Florida, New Jersey, New York, and Minnesota were evaluated. Data collection process involved visual inspections, damage surveys, corrosion testing including continuity, one-point resistivity, four-point resistivity, half-cell potentials, and three-electrode linear polarization, reinforcement cover depths, chloride samples. The Virginia bridge deck was built with epoxy-coated reinforcement as top reinforcement mat and black bar as the bottom mat. The Florida bridge is a segmental prestressed box girder structure built with black bar. The New Jersey bridge deck was overlaid with latex modified concrete. The New York bridge deck, which was built in 1990, is six inch concrete topping over prestressed adjacent box beams structure with epoxy-coated bar in the negative moment area. The Minnesota bridge was rebuilt in 1984. The deck was rebuilt with epoxy coated reinforcing steel in the top and bottom mats. The probabilistic Fickian model requires reinforcement cover depths, surface chloride concentration, chloride initiation concentration, and diffusion coefficients as input parameters. The chloride initiation concentration was input via parametric bootstrapping, while the other parameters were input as simple bootstrapping. Chloride initiation concentration was determined from the chloride concentration at the reinforcement bar depths. The modeling results showed that the deterioration of the Virginia bridge deck was corrosion controlled and the bridge will undergo increasingly severe damage in the future. Florida bridge deck is not undergoing corrosion and will not experience corrosion damage within 100 years. New Jersey bridge deck's service life has been most likely extended by the overlay. Deterioration of the New York bridge was not corrosion controlled, but was related to longitudinal cracking of the topping at match lines of adjacent box beams. Minnesota bridge deck is delaminated and contained a large number of cracks that should be included in service life modeling; otherwise the service life estimate is underestimated. In addition to service life corrosion performance modeling, analyses were conducted on the relationships and interrelations of resistivity, corrosion potential, corrosion current and chloride at the reinforcing bar depth.
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    Creep and Shrinkage of a High Strength Concrete Mixture
    Townsend, Bradley Donald (Virginia Tech, 2003-05-08)
    In addition to immediate elastic deformations, concrete undergoes time-dependent deformations that must be considered in design. Creep is defined as the time-dependent deformation resulting from a sustained stress. Shrinkage deformation is the time-dependent strain that occurs in the absence of an applied load. The total strain of a concrete specimen is the sum of elastic, creep, and shrinkage strains. Several test beams for the Pinner's Point Bridge have been produced by Bayshore Concrete Products Corp., in Cape Charles, VA. These beams feature high strength concrete mix designs with specified 28-day compressive strengths of 55.2 MPa (8,000 psi) and 69.0 MPa (10,000 psi). These test beams were equipped with thermocouples to track interior concrete temperatures, and vibrating wire gages placed at the center of prestressing to record changes in strain. Laboratory creep and shrinkage testing was conducted on specimens prepared with identical materials and similar mixture proportions to those used at Bayshore. The temperature profile from the test beams during steam curing was used to produce match-cured specimens for laboratory testing. Two match cure batches were produced, along with two standard cure batches. Creep specimens from each batch were placed in the creep room and loaded to 30 percent of their after-cure compressive strength. The creep room had a temperature of 23.0 ± 1.7 °C (73.4 ± 3 ºF) and relative humidity of 50 ± 4 %. Companion shrinkage specimens were also placed in the creep room. Measurements were taken on the creep and shrinkage specimens using a Whittemore gage. Four cylinders were also equipped with embedded vibrating wire gages (VWGs) so that the interior and exterior strains could be compared. The Whittemore and VWG elastic and creep strains were similar, while the VWGs recorded significantly less shrinkage. The measured creep and shrinkage strains were compared to seven different models to determine which model was the most accurate. The models considered were ACI 209, ACI 209 modified by Huo, CEB Model Code 90, AASHTO-LRFD, Gardner GL2000, Tadros, and Bazant B3. The ACI 209 modified by Huo was most accurate in predicting time-dependent strains.
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    Creep of high-strength normal and lightweight concrete
    Edward C. Vincent; Bradley D. Townsend; Weyers, Richard E. (Virginia Center for Transportation Innovation and Research, 2004-05-01)
    In addition to immediate elastic deformations, concrete undergoes time-dependent deformations that must be considered in design. Creep is defined as the time-dependent deformation resulting from a sustained stress. Shrinkage deformation is the time-dependent strain that occurs in the absence of an applied load. The total strain of a concrete member is the sum of elastic, creep, and shrinkage strains. Test beams for the Pinner's Point Bridge were produced by Bayshore Concrete Products Corp. using a high-strength normal weight concrete (HSC) mixture and the Chickahominy River Bridge beams using a high-strength lightweight concrete (LTHSC) mixture. The test beams and the Chickahominy River Bridge beams were fabricated with thermocouples to track interior concrete temperatures, and vibrating wire gages (VWGs) were placed at the center of prestressing to record changes in strain. Laboratory creep and shrinkage testing was conducted on specimens prepared with identical materials and similar mixture proportions in the casting of the bridge beams. The temperature profile from the beams during steam curing was used to produce match-cured specimens for laboratory testing. Two match-cured batches were produced, along with two standard cured batches. The creep room had a temperature of 23.0 1.7C (73.4 3F) and a relative humidity of 50 4%. Companion shrinkage specimens were also placed in the creep room. Measurements were taken on the creep and shrinkage specimens using a Whittemore gage. Four HSC cylinders were also equipped with embedded VWGs so that the interior and exterior strains could be compared. The Whittemore and VWG elastic and creep strains were similar, while the VWGs recorded significantly less shrinkage. The measured creep and shrinkage strains were compared to different prediction models to determine which model was the most accurate. The models considered were ACI 209, ACI 209 modified by Huo, CEB Model Code 90, AASHTO-LRFD, Gardner GL2000, Tadros, and Bazant B3. The ACI 209 modified by Huo was the most accurate in predicting time-dependent strains for the HSC mixture. The best overall predictor for the LTHSC time-dependent deformations was the Gardner GL 2000 model for the standard cure LTHSC specimens, whereas the ACI 209 model was the best predictor of the total stains and individual time-dependent deformations for the match-cured LTHSC mixture.
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    Design and Behavior of Precast, Prestressed Girders Made Continuous — An Analytical and Experimental Study
    Newhouse, Charles David (Virginia Tech, 2005-04-21)
    Over the past fifty years, many states have recognized the benefits of making precast, prestressed multi-girder bridges continuous by connecting the girders with a continuity diaphragm. Although there is widespread agreement on the benefits of continuous construction, there has not been as much agreement on either the methods used for design of these systems or the details used for the continuity connections. To aid designers in choosing the most appropriate method, an analytical and experimental study was undertaken at Virginia Tech. Analyses were done to compare the differences in the predicted continuity moments for different design methods and assumptions over a range of commonly used systems of Precast Concrete Bulb Tee (PCBT) girders and cast-in-place slabs. The results of the analyses were used to develop three continuity connection details for testing during the experimental study. Three different continuity connections were tested using full depth PCBT 45 in. deep girders made continuous with a 6 ft wide slab. The bottom of the ends of the girders were made continuous with the continuity connection by extending prestressing strands for one test and extending 180 degree bent bars for the other test. Both connections adequately resisted service, cyclic, and ultimate loads. But, the test with the extended bars remained stiffer during cyclic loading and is recommended for use. A third test was performed on a system using only a slab cast across the top of the girders. Two primary cracks formed above the ends of the girders at the joint during service testing, after which no significant increase in damage took place. Results from the analytical study indicate that the predicted positive thermal restraint moments may be significant, similar in magnitude to the actual positive cracking moment capacities. Results from the experimental study indicate that restraint moments develop early due to thermal expansion of the deck during curing and subsequent differential shrinkage; however, the magnitudes of the early age restraint moments are much less than conventional analyses predict.