Browsing by Author "French, Catherine E."

Now showing 1 - 9 of 9
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    Bond Behavior of Uncoated and Epoxy-Coated Reinforcement in Concrete
    (1992-05) Grundhoffer, Timothy M.; French, Catherine E.; Leon, Roberto T.
    This report summarizes an experimental program conducted to investigate the bond behavior of epoxy-coated and uncoated reinforcement in concrete. The objectives were to investigate the effect of bar surface (epoxy, uncoated), concrete strength (6, 10, 12, 14 ksi), addition of micro silica to concrete (6, 10, 12 and 14 ksi concrete with micro silica and 6 and 10 ksi concrete without micro silica), and bar size (No. 6, No. 8, No. 11). Undisturbed rebar strain distribution along the development length was determined for epoxy-coated and uncoated bars using strain gages embedded inside the rebar. This was the first time the strain distribution of epoxycoated rebar had been measured. Ninety-six inverted half-beam specimens were tested while monitoring load, initial cracking load, free-end slip, and loaded-end slip. Four of the 96 specimens (2 uncoated, 2 epoxy-coated) had test bars with internally embedded strain gages. All of the specimens were designed to fail in bond by splitting of the concrete. All of the bars were cast with at least 12 in. of concrete above the bar (bottom cast). The reinforcement of a particular size was from the same heat of steel with the N type deformation pattern. A bond failure hypothesis for epoxy-coated bars is presented. The results were evaluated and compared to current design codes and previous research.
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    Development Length of GFRP Reinforcement in Concrete Bridge Decks
    (Minnesota Department of Transportation, 2000-07-01) Hanus, Joe; Shield, Carol K.; French, Catherine E.
    This report summarizes an experimental program that investigated the developement length and variability in bond of glass-fiber-reinforced-polymer (GFRP) reinforcement in concrete. The variables in the study were manufacturer (Marshall Industries Composites, Inc. [M1] and Corrosion Proof Products/Hughes Brothers [M2]), bar size (No. 5 and 6), cover (2 and 3 bar diameters), and embedment length (10 through 47 in.). Eighty-four inverted half-beam bond specimens were tested while monitoring load, loaded-end slip, free-end slip, cracking, and acoustic emissions on the embedded bar and concrete. Neither bar was recommended for immediate use as reinforcement in bridge decks. The M1 rebar exhibited cracking and splitting along the outer coating of the bar which damaged bar deformations. Additionally these bars exhibited larger COVs for bar failures with average ultimate loads below the reported manufacturer's value. The M2 rebar exhibited a smaller COV for tensile test bar failures and a similar ultimate load average when compared to the manufacturer's reported strength. However, both GFRP rebar had 47.0 in. embedment length bond tests which exhibited bar failures with ultimate loads less than the tensile test average minus two standard deviations. Keywords: Bond, GFRP Rebar, Bridge Decks
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    Freeze-Thaw Durability of High-Strength Concrete
    (Minnesota Department of Transportation, 1998-01) Kriesel, Roxanne; French, Catherine E.; Snyder, Mark
    This report presents freeze-thaw durability results of anin vestigation regarding the application ofhigh performance concrete (HPC) to prestressed bridge girders. This study included a total of 30 concrete mixes and more than 130 specimens, with the following variables: aggregate type, round river gravel, partially-crushed gravel, granite, high-absorption limestone, and low-absorption limestone; cementitious material composition, Type III portland cement only, 20 percent fly ash, 7.5 percent silica fume, and combination of 20 percent fly ash with 7.5 percent silica fume replacement by weight of cement; and curing condition heat-cured or seven-day moist-cured. No air-entraining agents were used in the study's initial phase to simulate the production of precast/prestressed bridge girders. Results indicate that it is possible to produce portland cement concrete with high strength and freeze thaw durability without the use of air-entraining agents. Overall, the moist-cured concrete specimens exhibited better freeze-thaw durability than the heat-cured concrete specimens. The reference concrete mixes--containing only portland cement-performed better than the concrete containing pozzolan material of fly ash or silica fume. The low-absorption limestone aggregate concrete mixes exhibited the best freeze-thaw durability performance--in some cases, enduring more than 1,500 freeze-thaw cycles without failing. The study found that the moisture content of the coarse aggregate at the time of mixing had a significant impact on the concrete's freeze-thaw durability.
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    Instrumentation and Fabrication of Two High-Strength Concrete Prestressed Bridge Girders
    (Minnesota Department of Transportation, 1998-01) Kielb, Jeffrey; French, Catherine E.; Leon, Roberto T.; Shield, Carol K.
    This report describes the design, instrumentation, construction, and test set-up of two high-strength concrete prestressed bridge girders. The girder specimens were constructed to evaluate prestress transfer length, prestress losses, flexural fatigue, ultimate flexural strength, and ultimate shear strength. Each test girder was a 132.75-foot long, 46-inch deep, Minnesota Department of Transportation (Mn/DOT) 45M girder section reinforced with 46 0.6-inch diameter 270 ksi prestressing strands. The 28-day nominal compressive strength of the girders was 10,500 psi. Each girder was made composite with a 9-inch thick, 48-inch wide composite concrete deck cast on top with a nominal compressive strength of 4000 psi. Girder I used a concrete mix incorporating crushed limestone aggregate while Girder II utilized round glacial gravel aggregate in the mix with the addition of microsilica. In addition, the two test girders incorporated two different end patterns of prestressing--draping versus a combination of draping and debonding--and two different stirrup configurations--standard Mn/DOT U versus a modified U with leg extensions. More than 200 strain gages were imbedded in each girder during construction. Other reports present flexural and shear testing results.
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    Mechanical Properties of High Strength Concrete
    (Minnesota Department of Transportation, 1998-01) Mokhtarzadeh, Alireza; French, Catherine E.
    Researchers conducted an experimental program to investigate production techniques and mechanical properties of high-strength concrete and to provide recommendations for using these concretes in manufacturing precast/prestressed bridge girders. High-strength concretes with 28-day compressive strengths in the range of 8,000 to 18,600 psi (55.2 to 128 MPa) were produced. Test variables included total amount and composition ofcementitious material, portland cement, fly ash, and silica fume; type and brand of cement; type of silica fume, dry densified and slurry; type and brand of high-range water-reducing admixture; type of aggregate; aggregate gradation; maximum aggregate size; and curing. Testing determined the effects of these variables on changes in compressive strength and modulus of elasticity over time, on splitting tensile strength, on modulus of rupture, on creep, on shrinkage, and on adsorption potential as an indirect indicator of permeability. The study also investigated the effects of test parameters such as mold size, mold material, and end condition. More than 6,300 specimens were cast from approximately 140 mixes over a period of three years.
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    Reusability and Impact Damage Repair of Twenty-Year-Old AASHTO Type III Girders
    (1992-01) Olson, Steven A.; French, Catherine E.; Leon, Roberto T.
    Prestressed concrete has been used as a bridge construction method in the United States since 1949. Presently, there are thousands of pretensioned prestressed concrete bridges in service in North America. Each year, approximately 200 girders are damaged as a result of impact damage (primarily overheight vehicles striking a bridge from below). This thesis describes the results of a four girder test series which evaluated impact damage and repairs. The girders used for the study were fabricated in 1967 and placed in service. They were removed from service in 1984 as a result of a road realignment project. The objectives of the research project were: 1) to determine the effective prestress in the strands after 20 years, 2) to determine the influence of impact damage on girder performance, 3) to evaluate the performance of two impact damage repair schemes under static, fatigue, and ultimate loadings, and 4) to develop a model to estimate the strand stress ranges in damaged girders.
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    Self-Compacting Concrete (SCC) for Prestressed Bridge Girders
    (Minnesota Department of Transportation, 2008-10) Erkmen, Bulent; Shield, Carol K.; French, Catherine E.
    Researchers conducted an experimental program to investigate the viability of producing self-consolidating concrete (SCC) using locally available aggregate, and the viability of its use in the production of precast prestressed concrete bridge girders for the State of Minnesota. Six precast prestressed bridge girders were cast using four SCC and two conventional concrete mixes. Variations in the mixes included cementitious materials (ASTM Type I and III cement and Class C fly ash), natural gravel and crushed stone as coarse aggregate, and several admixtures. The girders were instrumented to monitor transfer length, camber, and prestress losses. In addition, companion cylinders were cast to measure the compressive strength and modulus of elasticity, and to monitor the creep and shrinkage over time. The viability of using several test methods to evaluate SCC fresh properties was also investigated. The test results indicated that the overall performance of the SCC girders was comparable to that of the conventional concrete girders. The measured, predicted, and calculated prestress losses were generally in good agreement. The study indicated that creep and shrinkage material models developed based on companion cylinder creep and shrinkage data can be used to reasonably predict measured prestress losses of both conventional and SCC prestressed bridge girders.
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    Shear Capacity of High-Strength Concrete Prestressed Girders
    (Minnesota Department of Transportation, 1998-05) Cumming, David A.; French, Catherine E.; Shield, Carol K.
    As part of a project at the University of Minnesota to investigate the application of high-strength concrete in prestressed girders, four shear tests were performed on high-strength concrete prestressed girders. Originally constructed in August 1993, the girders, Minnesota Department of Transportation (Mn/DOT) 45M sections were 45 inches deep. Each girder utilized 46 0.6-inch diameter prestressing strands on 2-inch centers. The girders were designed assuming a 28-day compressive strength of 10,500 psi. Later, a 4-foot-wide and 9-inch-thick composite concrete deck was added to each girder using unshored construction techniques. The shear test results were compared with predicted results from ACI 318-95 Simplified Method, ACI 318-95 Detailed Method (AASHTO 1989), Modified ACI 318-95 Procedure, Modified Compression Field Theory (AASHTO LRFD 1994), Modified Truss Theory, Truss Theory, Horizontal Shear Design (AASHTO 1989), and Shear Friction (AASHTO LRFD 1994). The calculated shear capacities were in all cases conservative compared to the actual shear capacity.
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    Transverse Cracking in Concrete Bridge Decks
    (Minnesota Department of Transportation, 1999-01-01) French, Catherine E.; Eppers, Laurice J.; Le, Quoc T.; Hajjar, Jerome F.
    This study sought to determine the dominant parameters that lead to premature transverse cracking in bridge decks and to make recommendations that help reduce cracking tendency in bridge decks. The project includes two main parts: a field study and a parametric study. The field study identified 72 bridges in the Minneapolis/St. Paul area and explored the correlation between the observed cracking of those bridges and available design, material, and construction-related data. The parametric study investigated the relative influence of the factors that affect transverse deck cracking through a controlled nonlinear analysis study. Variables included: shrinkage, end restraint, girder stiffness, supplemental steel bar cutoff, cross frames, splices, deck concrete modulus of elasticity, and temperature history. In addition, four bridges from the companion field study were modeled to compare the analytical results with the actual crack patterns. Based on these results and correlation with other research, the study identified the following dominant factors affecting transfer cracking: shrinkage, longitudinal restraint, deck thickness, top transverse bar size, cement content, aggregate type and quantity, air content, and ambient air temperature at deck placement. Recommended practical improvements to bridge deck construction, in order of importance, include: using additives to reduce shrinkage of the deck concrete, using better curing practices, and minimizing continuity over interior spans.