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6 CHAPTER TWO LITERATURE FINDINGS AND SPECIFICATIONS A review of the literature that pertains to TPOs is presented. 7. Polymer wearing surfaces may lose toughness and Thin polymer overlays consist of a polymer binder and ductility as they age under ultraviolet exposure. The aggregates with a thickness not exceeding 25 mm (1 in.). application of a thin, asphaltic chip seal coat may be economically viable in order to extend the lives of TPOs by shielding them from ultraviolet exposure USES OF THIN POLYMER OVERLAYS and abrasive wear. Harper (7 ) observed that "epoxy polymer overlays are not a Sprinkel (4) states that the bridges that are the most likely `repair' for bridge decks. They are only a means of protect- candidates for TPOs (1) "are those that are in need of a skid- ing a deck that is in fairly good condition but is at risk for resistance wearing and protective surface but have peak- chloride and water penetration." Based on the experience in hour traffic volumes that are so high that it is not practical Alberta, Carter (8) states that-- to close a lane to apply the surface except during off-peak traffic periods" and (2) "are those in which increases in dead 1. TPOs properly applied can provide service lives of up load, reductions in overhead clearance, and modifications to to 20 years, but that maintenance will be required if joints and drains must be held to a minimum." the surface is intended to remain free of defects. Multiple-Layer Overlays 2. TPOs can be used in high salt environments to extend the lives of existing bridges containing noncoated According to Sprinkel (4), multiple-layer overlays are best steel even if some corrosion has begun prior to repair. used on decks that have good ride quality because the over- lays follow the contours of the deck surface. This is the result 3. TPOs are economically competitive with other of the layers being of uniform thickness, which results in repairs, especially when a minimum of repairs to the the overlays following the surface irregularities instead of deck are required and a minimum of resin is used, bringing the surface to a uniform grade. that is, the overlay thickness is less than 10 mm (0.40 in.). Slurry and Premixed 4. TPOs are more suited for preservation than for reha- Decks that have many surface irregularities are the best can- bilitation. Resins are too expensive to be used on didates for slurry and premixed TPOs (4). excessively rough or deteriorated concrete surfaces because considerable material would be required to bring the surface to grade. They can be used to extend PRE-OVERLAY EVALUATION the service lives of dense concrete overlays that are extensively cracked or to prevent freezing and thaw- The Missouri DOT performed an investigation of the cause ing damage to decks with inadequate entrained air of failures of the epoxy overlays that they had installed. void systems. Harper's (7 ) observations related to failures involving TPOs are as follows: 5. TPO installation requires specialized expertise. The primary failures observed in Alberta have been the Missouri recommends placing TPOs on decks that have result of workmanship or contractor-related errors. less than 5% of the deck requiring repairs. It is impor- tant that decks be tested for delamination, chloride lev- 6. Crack repairs are risky and are often a waste of els, and tensile strength of the concrete deck. Decks money. Most nonworking, nonrepaired cracks will that require less than 5% of surface to be repaired have not reflect through TPO wearing surfaces within 5 more likelihood of success. years. Many working cracks will eventually reflect Many of the failures appeared to be a failure of the top whether repaired or not. surface of the concrete deck instead of the polymer.