Browsing by Subject "Corrosion"

Now showing 1 - 9 of 9
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    Corrosion Investigation of Reinforcing Bars in Pavements and Bridge Decks Part II: Chloride Penetration/Rebar Corrosion Mechanisms
    (University of Minnesota, 1991-02-19) Jang, J.W.; Iwasaki, I.
    The main factors that influence the initiation and propagation of rebar corrosion in concrete are concrete properties, aggressive corrosive elements from the environment and concrete, and defects of the reinforcing material. The presence of chloride ion appears to be the dominant cause for rebar corrosion in concrete. Rebar corrosion is complex and the basic mechanisms of individual factors are not well understood because of the complex nature of physical and electrochemical factors and because of their interdependence. A visualization technique was developed for use in our laboratory for the determination of chloride ion distribution and concentration near the reinforcements in concrete. A galvanic current measurement technique was developed for estimating the corrosion rates of rebars in simulated concrete solutions and for investigating the effects of relevant parameters that may be responsible for macro-cell corrosion on rebars as a function of chloride ion concentration. The corrosion mechanism of rebars was explored by using the galvanic current measurement method as well as by using optical and scanning electron microscopy. The compounds that combine the properties of a corrosion inhibitor and a surfactant were explored for retardation of rebar corrosion. Organic compounds slowed the corrosion of rebars acting as an adsorption-type inhibitor. Organic compounds developed hydrophobic surfaces on concrete. Such an observation implies that salt solution may be prevented from penetrating the microcracks in concrete. Appendix I contains "Visualization of Chloride Distribution in Concrete," an abridgment submitted to the Transportation Research Board 70th Annual Meeting (1991). Appendix II contains "Rebar Corrosion under Simulated Concrete Conditions Using Galvanic Current Measurements," a paper submitted to the Transportation Research Board 70th Annual Meeting (1991).
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    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.
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    Crack and concrete deck sealant performance
    (2013-05) Johnson, Karl Andrew
    The 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.
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    Development of Best Practices for Inspection of PT Bridges in Minnesota
    (Minnesota Department of Transportation, 2012-04) Berg, Kyle Matthew; Schokker, Andrea J.
    This report focuses on post-tensioned bridges built in Minnesota prior to 2003. The scope is limited to providing a targeted check of bridges that are most likely to have grouting related corrosion problems based on a review of plans and inspection notes. The project consisted of three phases: 1) review of plans and inspection reports of 40 post-tensioned bridges constructed prior to 2003, 2) selection of 10 bridges for a limited onsite inspection of the exterior of the bridge, and 3) invasive inspection of three select bridges. The bridges were selected to represent different bridge construction types to provide a spot check of the post-tensioned bridge inventory in Minnesota. One of the three bridges has corrosion and voids due to poor grouting, one has major corrosion problem related to construction issues (but appears to have good grout), and one showed no tendon corrosion or grouting problems during the invasive spot checks. Recommendations are given at the end of the report specific to the bridges that were investigated as well as for a general inspection plan for post-tensioned bridges in Minnesota. A concise guide for bridge inspection staff is provided that is specific to post-tensioned bridges.
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    Effect of FRCM Repair on the Bond Behavior of Corroded Reinforced Concrete Beams Subjected to Static and Cyclic Loading
    (2017-08) Anderson, Miranda
    This paper presents the evaluation of the effectiveness of Fiber Reinforced Cementitious Matrix (FRCM) repair in improving the bond behavior of corroded reinforced concrete beams under both static and fatigue loading. The study consisted of 30 full-scale beams, both corroded and uncorroded. The variables used in this study were corrosion level based on mass loss, repair method used, type of loading (monotonic or repeated loading), and load range applied. Corrosion was found to reduce the fatigue strength of reinforced concrete beams by introducing internal stresses in the concrete that ultimately cause reduction in the bond between the reinforcement and the surrounding concrete. FRCM was found to increase the fatigue strength of corroded concrete beams by providing confinement, thus making it an effective method for repairing beams damaged from corrosion. The use of a cementitious substrate with FRCM allowed for easier monitoring of the cracks developed in the concrete while testing.
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    Effect of Reinforcing Bar Chemical Composition on Corrosion Resistance
    (Minnesota Department of Transportation, 1994-10) Leon, Roberto T.; Jeon, Moon-Gu
    This research report looks at the chemical composition of reinforcing bars, and the sulfur content in particular, and their influences on the corrosion resistance of rebar. The research supports the original hypothesis--which suggests that the reduction in sulfur inclusions would benefit corrosion resistance. The reduction could result in significant savings that would more than offset the higher initial costs for these bars. To test the hypothesis, the study examined the corrosion resistance of four kinds of steel reinforcing bars; ordinary, low sulfur, copper and tungsten, and nickel. As in other series in the past, this research indicates conflicting results for different measurement techniques used to quantify corrosion rates. In addition, the mechanism that results in low sulfur bars showing a three-fold increase in corrosion life are not clear and need more study. The report recommends a long-term follow-up study on the use of both small cube and slab specimens in the laboratory, as well as full-scale specimens in the field.
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    Fine-Scale Bacterial Community and Chemical Changes within Steel Corrosion Tubercles in the Duluth-Superior Harbor
    (2016-10) Thomas, Jo Jo
    Corrosion of steel structures in the Duluth-Superior Harbor (DSH) is a severe economic problem. This corrosion is characterized by deep pits covered by crusty, orange, blister-like structures called tubercles. Prior research demonstrated these tubercles contain both iron-oxidizing (IOB) and sulfate-reducing bacteria (SRB) but fine scale changes of bacterial community structure within these tubercles remain unknown. Experimental steel coupons were placed at four sites in the DSH in 2006 and 2012 and recovered in 2013 to measure chemical gradients and identify bacteria associated with young and old corrosion tubercles. Oxygen concentrations measured with microelectrodes decreased from saturation in the overlying water to nearly anoxic conditions at the surface of tubercles while ferrous iron (Fe2+) concentration increased with depth inside the tubercles. Bacterial DNA from different regions of the tubercles was sequenced using a next-generation sequencing technique to characterize the bacterial communities. Bacterial community composition changed within the tubercles. Families containing bacteria that oxidize iron and sulfur were consistently found on the outsides of tubercles and on non-tubercle steel. Families with bacteria that reduce iron and sulfur were found on the undersides of tubercles and in corrosion pits on the steel surface. Iron-oxidizing bacteria were more abundant after 0.8 years than 6.6 years and were distributed throughout tubercles while sulfate-reducing bacteria were most abundant in corrosion pits. Combined, these data are consistent with the cathodic depolarization (differential aeration cell model) and direct electron transfer theories of pitting corrosion, which provide explanations for the roles of bacteria in the accelerated corrosion of steel structures.
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    Image Analysis Of Corrosion Pit Initiation On ASTM Type A240 Stainless Steel And ASTM Type A 1008 Carbon Steel
    (2016-02) Nine, H M Zulker
    The adversity of metallic corrosion is of growing concern to industrial engineers and scientists. Corrosion attacks metal surface and causes structural as well as direct and indirect economic losses. Multiple corrosion monitoring tools are available although those are time-consuming and costly. Due to the availability of image capturing devices in today’s world, image based corrosion control technique is a unique innovation. By setting up stainless steel SS 304 and low carbon steel QD 1008 panels in distilled water, half-saturated sodium chloride and saturated sodium chloride solutions and subsequent RGB image analysis in Matlab, in this research, a simple and cost-effective corrosion measurement tool has identified and investigated.Additionally, the open circuit potential and electrochemical impedance spectroscopy results have been compared with RGB analysis to gratify the corrosion. Additionally, to understand the importance of ambiguity in crisis communication, the communication process between Union Carbide and Indian Government regarding the Bhopal incident in 1984 was analyzed.
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    Microbiological and chemical aspects of corrosion of sheet steel in the Duluth-Superior Harbor
    (2010-12) Bostrom, Jonathan Robert
    Steel structures in the Duluth-Superior harbor show unusual patterns of corrosion characterized by raised blister-like nodules called tubercles and pitted steel. This corrosion phenomenon could possibly decrease the integrity and the lifespan of the structures. Microbiological and chemical factors that may be influencing corrosion processes were examined in this study from 2007-2009. A laboratory microcosm experiment was designed to examine several microbiology and water quality parameters. Terminal-restriction fragment length polymorphism (T-RFLP) analyses showed that bacterial communities on steel were different from one another in microcosm treatments with different types of water (e.g. autoclaved Duluth-Superior harbor water vs. unaltered Duluth-Superior harbor water and Lake Superior water vs. Duluth-Superior harbor water). Coupons with different bacterial communities also showed differences in sulfate-reducing bacterial abundance and iron-oxidizing bacterial abundance. Further, coupons with higher abundances of sulfate-reducing bacteria and iron-oxidizing bacteria had higher inverse polarization resistance values. Inverse polarization resistance is frequently used to approximate the instantaneous rate of corrosion. Mass lost and pit depth were measured on steel in the microcosm, and these two measurements showed a positive correlation. Microbiological and corrosion measurements were also performed on steel in the Duluth-Superior harbor, and these measurements were compared to steel in the microcosm experiment. These experiments showed correlations among water chemistry, bacterial community, and populations of specific bacteria that are associated with corrosion in other ecosystems.