Browsing by Subject "Concrete"
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Item Advancements in Imaging of Concrete Members Using Shear Waves(2018-12) Asadollahi, AzizThe emergence of linear array devices employing dry point contact transducers emitting horizontal shear waves significantly increased the efficiency of data acquisition and enabled using imaging techniques for nondestructive evaluation of concrete members. Reverse time migration (RTM) is a mechanics-based imaging technique that has gained the attention of researchers in the context of nondestructive testing (NDT) in recent years. RTM offers a better focusing over synthetic aperture focusing technique (SAFT), a well-established real-time imaging method for NDT of concrete members, and enables locating reflectors with steep slopes and the bottom boundaries of embedded objects. Despite all advantages, RTM suffers from some limitations. It is computationally costly and demands a massive memory. In addition, RTM algorithm generates images with high-amplitude artifacts and assigns amplitudes to the points of a reconstructed image that are not a true representative of the reflectivity of the scanned medium at those points. This dissertation develops an analytical approach to resolve the computational cost and memory demand bottlenecks of the RTM when dry point contact transducers emitting horizontal shear waves are used for data acquisition. Horizontal shear waves preserve more energy than longitudinal waves after emission allowing inspection of concrete members in deeper depths. However, the lower wavelength of shear waves increases the potential of scattering by aggregates and air voids that affects the quality of the reconstructed images. This dissertation develops a 3D numerical tool to study the scattering attenuation of shear waves in concrete. An efficient algorithm is introduced to generate non-overlapping aggregates and air voids to study the effect of size, shape, and material properties of aggregates as well as the porosity of concrete on the scattering attenuation of shear waves. Moreover, it develops novel techniques to mitigate the high-amplitude artifacts of RTM images and to adjust the amplitudes assigned to the points of an image reconstructed by RTM for homogeneous and concrete members.Item Anchorage of shear reinforcement in prestressed concrete bridge girders(2014-06) Mathys, Brian ThomasThe Minnesota Department of Transportation has typically used epoxy coated straight legged stirrups anchored in the tension zone as transverse reinforcement in prestressed concrete bridge girders. With the straight legs of the U-shaped stirrups anchored into the bottom flange of the girders, this configuration is readily placed after stressing the prestressing strands. American Concrete Institute (ACI) and American Association of State Highway and Transportation Officials (AASHTO) specifications require stirrups with bent legs that encompass the longitudinal reinforcement to properly anchor the stirrups. Such a configuration is specified to provide mechanical anchorage to the stirrup, ensuring that it will be able to develop its yield strength with a short anchorage length to resist shear within the web of the girder. AASHTO specifications for anchoring transverse reinforcement are the same for reinforced and prestressed concrete; however, in the case of prestressed concrete bridge girders, there are a number of differences that serve to enhance the anchorage of the transverse reinforcement, thereby enabling the straight bar detail. These include the precompression in the bottom flange of the girder in regions of web-shear cracking. In addition, the stirrup legs are usually embedded within a bottom flange that contains longitudinal strands outside of the stirrups. The increased concrete cover over the stirrups provided by the bottom flange and the resistance to vertical splitting cracks along the legs of the stirrups provided by the longitudinal prestressing reinforcement outside of the stirrups help to enhance the straight-legged anchorage in both regions of web-shear cracking and flexure-shear cracking. A two-phase experimental program was conducted to investigate the anchorage of straight legged epoxy coated stirrups that included bar pullout tests performed on 13 subassemblage specimens which represented the bottom flanges of prestressed concrete girders in a number of configurations to determine the effectiveness of straight legged stirrup anchorage in developing yield strains. Additionally, four girder ends were cast with straight legged stirrup anchorage details and tested in flexure-shear and web-shear. The straight leg stirrup anchorage detail was determined to be acceptable for Minnesota Department of Transportation M and MN shaped girders as nominal shear capacities were exceeded and yield strains were measured in the stirrups prior to failure during each of the tests.Item 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.Item Calibration of New Concrete Shrinkage and Creep Model for ACI Committee 209(2022-04) Clement, TimothyA new semi-empirical concrete shrinkage and creep model is proposed and calibrated in which creep ages according to solidification theory. The impetus for this CRC-funded research is to propose new creep and shrinkage design guidelines for ACI Committee 209; previous guidelines were published in 1982 and are no longer up to date with modern understanding of time-dependent behavior. The new model proposes a coupling between autogenous and drying shrinkage using a volume-average pore relative humidity and treats drying creep as an additional stress-dependent shrinkage, linking together all these phenomena. The proposed expressions are designed to facilitate traditional integral-type analysis, but also uniquely support rate-type calculations that can be leveraged by analysis software. Model calibration uses the Northwestern University (NU) database of creep and shrinkage tests to determine new model parameters. Profile likelihood curves for each individual mix in the database are computed to quantify the sensitivity of the fitting parameters to the available data and to mix design inputs.Item Concrete Overlays(Transportation Engineering and Road Research Alliance (TERRA), 2011-01) Transportation Engineering and Road Research Alliance (TERRA)This 2-page fact sheet provides information about concrete overlays, including their benefits and implementation.Item Corrosion of Coated and Uncoated Reinforcing Steel in Concrete(1992-05) Lorentz, Thomas E.; French, Catherine; Leon, Roberto T.An experimental program designed to investigate the effects of various material properties on the corrosion of reinforcing steel in concrete was conducted at the University of Minnesota. The test specimens were constructed to promote macrocell corrosion. A total of 96 prism and cracked slab specimens were subjected to an accelerated corrosion process for periods ranging from 35 to 48 weeks. The impact of the following variables on the corrosion of reinforcing steel in concrete was monitored in this program: 1) water/cementitious ratio; 2) addition of condensed silica fume; 3) percentage of entrained air in the concrete; 4) type of reinforcing steel and coating; 5) cracked concrete. The corrosion current, specimen resistance, driving potential, and CuCuS04 half-cell potential were monitored regularly to follow the corrosion process. The most significant variables determined in the University of Minnesota experimental program were the concentration levels (7.5% vs. 10%) of condensed silica fume (CSF), the significance of cracked concrete on the corrosion of reinforcing steel, and the lack of any notable corrosion resulting in concrete specimens containing bars with significantly damaged epoxy-coatings, despite high levels of chloride contamination.Item Crack and concrete deck sealant performance(2013-05) Johnson, Karl AndrewThe research objective of this project was to define the current state-of-the-art regarding the use of bridge deck sealants and crack sealers to extend the life of reinforced concrete bridge decks. The role of deck sealants and crack sealers is to prevent chloride ion ingress, originating from deicing materials spread on the road, from penetrating into the concrete bridge deck and corroding the reinforcing steel bars. The report includes the information generated from a literature review and survey. The literature review focused on current and significant studies in the field of deck and crack sealing. The intent of the survey is to determine common practices for the use and application of these sealers in different states throughout the United States. After all of the information is collected and compiled from the literature review and the survey, the best materials and practices are recommended for use in Minnesota and throughout the Midwest.Item The Effect of Composition on the Alkali-Silica Mitigation Potential of Fly Ash-Ground Glass Blends in Concrete(2019-08) Doolittle, NathanThis research investigates the use of ternary blends of Portland cement, ground glass and four different fly ashes as a mitigation method for alkali-silica reaction (ASR) in concrete. ASR is the reaction between select reactive aggregates and alkalis in the pore solution of concrete added by the hydration of portland cement. The inclusion of fly ash and waste glass has potential to reduce the deleterious expansive effect of ASR. Testing conducted involves measurement of length change, compressive strength and the fresh mix properties.Item Experimental Evaluation of Post-Cracking Deflection Behavior in Prestressed Concrete Beams(2022-08) Kulzer, AlexPrecast prestressed concrete beams are more efficient and effective than the traditional reinforced concrete beam, but their performance is more difficult to predict. This experimental thesis was run to quantitatively compare deflections between laboratory precast prestressed concrete beams to ACI 318-19 and PCI Design Handbook (8th edition) design methods. A full design and testing procedure is detailed for 12 rectangular beams with varying levels of partial prestressing to compare the effects of mild steel in prestressed beams. The rectangular beams are designed with uncracked, transition, and cracked sections at a constant service load. Testing procedures are detailed for full sized, typical double tee sections designed by Metromont. This research analyzed and commented on the performance of the different rectangular beams and double tees in relation to calculated deflection prediction curves. Additional comments are made on the cracking of the rectangular beams in relation to previous studies. Results from the rectangular beams deflections show a consistent low prediction in initial stiffness, varying results at service, and higher inaccuracy in post cracking predictions with increasing mild steel when using the effective moment of inertia and bilinear methods for predicting deflections. Cracking patterns show similar results from previous studies and vary when mild steel is introduced. Findings from this research conclude that the current methods for predicting deflections are not reliable in all situations.Item Freeze-Thaw Durability of High-Strength Concrete(Minnesota Department of Transportation, 1998-01) Kriesel, Roxanne; French, Catherine E.; Snyder, MarkThis 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.Item Impact resistance of filled concrete box sections(2013-08) Bruhn, Christopher MichaelThe purpose of this research is to analyze the effects of drop-weight impact tests on filled concrete box sections. Research in other areas of soil filled container walls has proved favorable in blast loading environments suggesting a concrete system may also work well. In the experiment, thirty different box sections were cast and broken via drop weight test with six different fill materials. The testing yielded that compacted sand is the most favorable fill material for the sections. The research results indicate that further testing and applications should use compacted sand as a fill material.Item 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.Item Nondestructive Evaluation Advancements for Damage Detection in Concrete(2016-06) Freeseman, KatelynWhile concrete is the most widely used civil engineering material, damage detection and progression in concrete structures have still proven to be difficult to address, especially when only one-sided access is available. New technological advances in nondestructive testing technology have created the opportunity to better utilize ultrasonic waves to aid in this damage detection process. However, interpretation of the signal data is a challenging task which often requires subjective assessments. This thesis addresses these limitations via the utilization of ultrasonic array technology for nondestructive damage detection purposes. The ultrasonic shear velocity array system used for this research is particularly advantageous because it can obtain measurements on virtually any concrete specimen, from columns and beams to concrete pavements, and provides a wealth of data from a single measurement. Novel signal interpretation methods were developed for several important concrete applications. Detection of load-induced damage in laboratory beams and a full-scale reinforced concrete column, as well as standard life-cycle damage in concrete pavements caused by freeze thaw or alkali-silica reaction degradation were considered. These investigations culminated in the development of successful and efficient quantitative damage detection methods. Finally, the development and refinement of a simulation program allowed for verification of the experimental investigation and a greater understanding of signal results.Item 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.Item Source, Winter 2008(University of Minnesota Extension, 2008) University of Minnesota ExtensionItem Ultrasonic linear array evaluation of concrete pavements(2013-06) Hoegh, Kyle EdwardNondestructive evaluation is an important tool for assurance of proper construction practices and selection of rehabilitation procedures for civil infrastructure. Improvements in technology for testing of concrete structures, such as the introduction of dry point contact ultrasonic arrays, allow for collection of repeatable and spatially diverse shear wave impulse time-histories. This dissertation deals with development of methods that can be used for quantitative evaluation of concrete pavement structures using ultrasound linear array systems. The synthetic aperture focusing technique was adapted to handle spatially diverse measurement pairs. Kirchoff migration and the Hilbert transform were utilized to correlate high intensity portions of the instantaneous amplitude time history envelopes to the physical location of changes in acoustic impedance of the tested medium. To mitigate the effect of limited aperture, the interpretation methods were generalized to accommodate virtual array systems and implemented to create two- and three-dimensional reconstructions of the subsurface concrete structure. This reconstruction analysis was applied for practical pavement problems such as reinforcement and layer boundary location, as well as stochastic flaw detection. Comprehensive ground truth validation on several full-scale concrete pavements confirmed the high resolution of the analytical tools developed in this dissertation.Item Wakota Bridge Thermal Monitoring Program Part I: Analysis and Monitoring Plan(Minnesota Department of Transportation, 2013-05) Scheevel, Christopher J.; Morris, Krista M.; Schultz, Arturo E.In this work, a common refined design method is evaluated with respect to a recently constructed bridge. Two finite element models of the Wakota Bridge in South St. Paul, Minnesota, were produced, one using a design level program (SAP2000) and the other using a research level program (ABAQUS). These models were verified with respect to each other using linearly elastic materials and were found to behave similarly. After this verification, an arbitrary temperature load was applied to each model and the refined design method was evaluated for accuracy of reduced section properties with respect to the more descriptive progressive cracking solution simulated by ABAQUS. The refined design method was employed using two, four, and six stiffness segments at which stiffness is evaluated along the height of the pier walls. It was seen that accuracy increased as the number of stiffness segments increased and that four segments seemed to balance accuracy and time-commitment by the engineer adequately. A staged construction model of the Wakota Bridge was also built, using the design level program, which incorporates all time-dependent effects of the construction sequence as well as locked-in forces. A pile analysis was performed and appropriate rotational springs were found for Foundations 2 and 3. A simplified method for the determination of the rotational springs is discussed, and a range of effective lengths was found for use with this procedure. The staged construction model is used for field data correlation in Part two of this report. The staged construction model was also used to evaluate the different design options as described in the AASHTO LRFD. The two options given for accounting for reduced section properties were evaluated and compared. The refined analysis option and gross section option were compared for the Wakota Bridge and are shown to correlate to within about 10%. The two temperature application methods (Procedure A and B in the AASHTO LRFD) were also compared. As expected, Procedure B produced much larger design moments than that of Procedure A.Item Wakota Bridge Thermal Monitoring Program Part II: Data Analysis and Model Comparison(Minnesota Department of Transportation, 2013-05) Morris, Krista M.; Schultz, Arturo E.In this work, a common refined design method is evaluated with respect to a recently constructed bridge. Two finite element models of the Wakota Bridge in South St. Paul, Minnesota were produced using a design level program (SAP2000). These models were analyzed and their results compared to the data collected from the bridge. The second half of this study concerned the comparison of the collected field data with the values produced by evaluating the design-level finite element models previously created in Phase I of the project, and calibrating these models to provide an accurate prediction of the future behavior of the bridge. This was done by calculating changes in axial force and moment from strain data collected from the Wakota Bridge and changing various parameters within the design level model (DLM) in order to calibrate the models to the field data. The model using the refined design method was shown to correlate to the superstructure field data to within 2 percent, while between 13 percent and 35 percent correlation was seen between the model deploying the gross section method and the field data. The pier behavior predicted by the two models showed much less correlation to the field data. After calibration, it was possible to predict the general trend of the pier behavior, but the values of changes in moment did not correspond to the field data. This was especially true in Pier 4. Further consideration of the model parameters is necessary to fully calibrate the models. The two temperature application methods (Procedure A and B in the AASHTO LRFD) were also compared. The internal concrete temperature ranges measured in the field were much closer to the range specified in Procedure A.