Browsing by Subject "Epoxy"

Now showing 1 - 3 of 3
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    Block copolymer modified epoxy: role of epoxy crosslink density.
    (2010-03) Thompson, Zachary John
    Epoxies of systematically varying crosslink density containing 5% by weight of a poly(ethylene oxide)-b-poly(ethylene-alt-propylene) (OP) block copolymer were prepared and characterized. The block copolymer self-assembled to form particles with diameters ranging from 15 to 100 nm. Transmission electron microscopy of the modified epoxies revealed that the block copolymer nanostructure can be altered by changing the epoxy crosslink density. The block copolymer structures displayed a decrease in surface curvature as the crosslink density was reduced. The strain energy release rate, Gc, of the block copolymer-modified epoxies, which can be related to fracture resistance, increased dramatically with a decrease in the epoxy network crosslink density and plateau at a value 13 times greater than the unmodified material. This trend was observed with both high and low molecular weight OP additives. The toughening behavior is dependent on the block copolymer nanostructure in highly crosslinked system while lightly crosslinked block copolymer-modified epoxies display similar fracture resistances for each block copolymer additive. Scanning electron microscopy of fracture surfaces revealed extensive voiding and plastic deformation near the crack tip of the modified epoxies. Addition of the block copolymer did not appreciably decrease the Young's modulus or glass transition temperature compared to the unmodified material. Epoxies with varying concentrations of block copolymer additive were prepared and further demonstrated the role of crosslink density on improving fracture resistance. Lightly crosslinked epoxies were able to maintain extraordinary toughness at block copolymer concentrations as low as 1 wt%. Increasing crosslink density decreases the toughening ability of the block copolymer and a higher concentration is required to provide adequate fracture resistance.
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    A Comprehensive Evaluation of High Friction Overlay Systems on Bridge Decks in Cold Climate Regions
    (2015-05) Kostick, Robert
    In recent history the Minnesota Department of Transportation has looked to improve the safety of bridge decks by installing high friction overlays (HFO). A comprehensive study researched four different proprietary HFO systems placed on fourteen bridge decks throughout Minnesota. Research was split into three separate tasks: (1) laboratory testing of aggregate properties, (2) field observations and testing, and (3) a comprehensive analysis of crash data investigated crash rates on bridges with HFO systems. Field observations and testing revealed that the use of snowplows quickly abrades HFO systems. Abrasion, among other factors, causes a reduction in surface friction values, and reduces the life of HFO systems. Furthermore, improving crash rate trends cannot be directly correlated to the installation of HFO systems. Research concludes that HFO systems should not be used in Minnesota. Other cold climate transportation agencies should conduct research emulated after this study to assess HFO systems in their jurisdiction.
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    Crack and Concrete Deck Sealant Performance
    (Minnesota Department of Transportation, 2009-03) Johnson, Karl; Schultz, Arturo E.; French, Catherine; Reneson, Jacob
    The objective of this project is 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 report includes the information generated from a literature review and survey which focused on current and significant studies in the field of deck and crack sealing. The intent of the survey was to determine common practices for the use and application of these sealers in different States throughout the United States. Based on the information collected from the literature review and the survey, the best sealant materials and application practices are recommended for use in Minnesota and throughout the Midwest. The report consists of four sections including: (1) a synthesis of the literature review on the background, application, and performance of concrete deck sealants and crack sealers; (2) a summary of the survey conducted by Mn/DOT to determine the current selection criteria, materials, application practices, and findings from different states in United States; (3) an assessment of selection criteria, materials, application practices, and performance; and (4) conclusions, recommendations and areas in need of further research.