Long-Term Performance of Polymer Concrete for Bridge Decks (2012) / Chapter Skim
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Pages 8-27
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From page 8... ...
. PRE-OVERLAY EVALUATION The Missouri DOT performed an investigation of the cause of failures of the epoxy overlays that they had installed.
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From page 9... ...
Polymer Concrete Application Rates Typical PC application rates for the three different types of overlays are given in AASHTO Guide Specifications (6)
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From page 10... ...
and ASTM C1583 (14) could be used to determine whether the size of shot, flow of shot, traveling speed of machine, and number of passes are adequate to provide the required surface preparation to achieve a minimum tensile bond strength of 1.7 MPa (250 psi)
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A primer is usually applied to the surface at an approximate rate of 0.41 kg/m2 (0.75 lb/yd2) to improve the bond strength (Figure 5)
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. The required viscosity, gel time, tensile elongation, and bond strength are shown in AASHTO Guide Specifications (6)
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In most cases, the information on the resins used did not include tensile elongation or modulus of elasticity; rather, the generic resin type was given, for example, epoxy, polyester-styrene, or methacrylate. Ohio Bridge Deck, 1983 Dimmick (18)
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From page 14... ...
An investigation of thin epoxy wearing surfaces installed by agency crews in the 1960s showed that some had performed well. Carter notes that on one bridge on which a coal tar epoxy overlay had been installed, 70% of the overlay was still intact and many of the failed areas appeared to have been caused by thermal incompatibility owing to an excessive thickness of epoxy having been applied.
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From page 15... ...
reports on 21 TPOs of a total of more than 100 that had been placed in Alberta beginning in the 1960s. Typically, it was found that the failure of TPOs resulted "from the basic incompatibility of polymer concrete and portland cement concrete, manifested as debonding or shearing of the overlay from the concrete." Many of the bridges had been overlaid previously with dense concrete that developed numerous cracks.
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From page 16... ...
It was concluded that "the extension of deck service life resulting from the thin overlays at these inferior concrete sites appears to be from 5 to 12 years. Since the cost of deck or entire bridge placement is so much higher than the overlay cost, these polymer systems were successful in reducing life cycle costs." It was noted that the deck life was significantly reduced when a significant amount of reflective cracking was present in the concrete.
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From page 17... ...
but differs by providing a swivel attachment to the cap and the top hook of the test device to minimize eccentricity. The results indicated little change in initial tensile bond strengths of more than 1.65 MPa (240 psi)
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From page 18... ...
provide a list of key projects using flexible epoxy binder that had been in service for 10 years. The authors provide a good summary of surface preparation, overlay application including multiple-layer method or slurry method, and curing quality assurance procedures, service life, trouble-shooting procedures, and loss of skid resistance.
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From page 19... ...
• The 12 epoxy overlays were found to be performing acceptably although several distresses were noted: – Short crack in one; – One appeared to have been poorly installed and exhibited small spalls; 90% of the overlay was intact and 80% to 90% of the friction aggregate remained; – Two were very thin owing to wear or installation, with 75% to 95% of the overlay remaining; – One had small delaminations, with 90 to 95% of the overlay remaining; and – The other seven were in very good to excellent condition, with 90% or more of the overlay remaining. New York DOT conducts friction tests annually and uses ground-penetrating radar to determine whether TPOs waterproof the decks and retard the corrosion rate.
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Test sections were placed using epoxy and MMA. Two epoxy test sections were installed, one using the slurry method and the other using the broom-and-seed method.
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. Pennsylvania Pennsylvania DOT installed three TPOs: premixed polyester, an epoxy multiple layer, and an epoxy urethane multiple layer, each on two separate bridge decks.
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Laboratory tests sought to duplicate the application. The initial tensile bond tests gave good strengths, but when they were performed after several months on the same specimens, the specimens that had been primed with the high-molecularweight methacrylate had low bond strengths.
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The surface was shot blasted, the primary anode system was installed, and the polymer concrete was placed and screeded to a 12-mm (0.5-in.) thickness.
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22 FIGURE 12 Shear stresses in overlays for various thickness and modulus ratios. (For assumed values of ΔεT = 500 μ-in./in., Es = 4 × 106 psi.)
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Four overlays were placed on bridge decks on I-81 in September and October 2005: two two-layer deicing overlays and two one-layer VDOT epoxy overlays. The overlays were treated approximately every 2 weeks with deicing salt brine at a nominal rate of 70.5 L per lane-kilometer (30 gal per lane-mile)
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From page 26... ...
Five snow experiments using artificially applied snow and one using artificial "black ice" were conducted. The results of the tests using artificial snow indicated that both deicing and epoxy overlays would improve the friction of bare, tined concrete pavements or bridge decks in the early stages of a snow storm before the snow removal equipment can arrive.
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From page 27... ...
1. Guide Specifications for Polymer Concrete Bridge Deck Overlays, AASHTO-AGC-ARTBA Task Force 34, Washington, D.C., 1995 (6)
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