Browsing by Author "Dymond, Benjamin Z."
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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 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.Item Load Rating Assessment of Three Slab-Span Bridges Over Shingle Creek(Minnesota Department of Transportation, 2022-08) Hill, Kendall A.; Dymond, Benjamin Z.; Hedegaard, Brock D.; Linderman, Lauren E.Three slab-span bridges crossing Shingle Creek in Brooklyn Center, Minnesota, have poor American Association of State Highway and Transportation Officials (AASHTO) load rating factors for certain truck configurations. Characterization of load distribution is useful for determining the load rating of bridges, but results in the literature have shown that the AASHTO code results in conservative load rating factors. The focus of this study was to determine if the load rating of the three concrete slab-span bridges was conservative and could be improved using results from live load testing and finite element analysis. Field testing used a suite of instrumentation that included displacement transducers, strain gauges, accelerometers, and tiltmeters. A three-dimensional solid-element finite element model was used to determine an expected range of behaviors and corroborate the field data regarding how load distributed when placed near and away from a barrier. In addition, a method for developing a simple plate model of slab span bridges was developed considering in-situ material properties and effects of secondary elements such as barriers. Results indicated that the AASHTO load rating was conservative, and an improved rating factor could be obtained considering the field test data and computational modeling results.