Browsing by Subject "Reinforcing bars"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Anchorage of Epoxy-Coated Rebar Using Chemical Adhesives(Minnesota Department of Transportation, 2019-02) Mills, Connor; Dymond, Benjamin Z.Post-installed reinforcement is used to connect a new concrete member to an existing concrete structure. Typically, uncoated rebar post-installed with a chemical adhesive is used in these applications, which may lead to corrosion. Departments of Transportation and local bridge owners have used and continue to use epoxy-coated rebar in post-installed applications due to its inherent corrosion resistance. Unfortunately, chemical adhesive manufacturers provide tensile strengths of their products for use with uncoated rebar and not epoxy-coated rebar. This work examined what effects the epoxy coating had on the tensile pullout strength and compared the results for epoxy-coated and uncoated rebar. Two slabs were constructed. One slab contained epoxy-coated rebar post-installed using four different chemical adhesive products and the other slab contained uncoated rebar post-installed using the same four different chemical adhesive products. Results indicated that the epoxy coating slightly reduced the tensile pullout strength of the post-installed rebar. The ratio of the tensile pullout strength of the epoxy-coated reinforcing bars to the tensile pullout strength of the uncoated reinforcing bars ranged from 0.94 to 1.05 and varied based on the chemical adhesive manufacturer. Results from t-test analyses indicated that differences in the tensile pullout strength for epoxy-coated rebar compared to uncoated rebar were statistically different when using three of the four chemical adhesives during installation. Recommendations were made to include a modification factor when calculating bond strength for an epoxy-coated reinforcing bar post-installed using chemical adhesives and to raise the MnDOT-specified uncracked bond stress (τuncr) of 1,000 psi or use the manufacturer published values for τuncr.Item 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).Item Deterioration of Mixed Rebar and Fiber-Reinforced Concrete Bridge Decks(Minnesota Department of Transportation, 2019-02) Treat, Corin; Dymond, Benjamin Z.Between 1973 and 1989, approximately 600 bridge decks were constructed in Minnesota with a top layer of epoxy-coated rebar and a bottom layer of uncoated rebar (i.e., mixed rebar deck) to potentially reduce corrosion in the top layer of rebar. In the last five years, at least 20 bridge decks were constructed with polypropylene fibers in the concrete mix to reduce the width and amount of cracking. This project investigated how mixed rebar or polypropylene fibers affected the rate of deterioration in bridge decks (e.g., spalling of underside of deck concrete or unsound concrete on the top wearing surface) compared to control structure decks of approximately the same age. Visual inspections were conducted on certain bridges to compare the visual degradation of the mixed rebar and fiber-reinforced decks with their control structure decks. The results were subdivided to indicate how the superstructure type, average daily traffic, route type, and wearing surface crack density affected the condition ratings and rate of deterioration. The mixed rebar decks reached worse condition states than the control structures when comparing the condition of the underside of the deck; steel superstructures had the largest negative affect on the deterioration. Recommendations included: create an inspection rating element for mixed rebar decks that quantifies the underside of deck crack density, use a robust crack sealing method on mixed rebar decks when they have been at NBE Element #12 CS2 for approximately 7 years, and continue comparing fiber-reinforced decks to control structure decks to analyze the deterioration over time.