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Long-Term Performance of Polymer Concrete for Bridge Decks (2012)

Chapter: CHAPTER TWO Literature Findings and Specifications

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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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Suggested Citation:"CHAPTER TWO Literature Findings and Specifications." National Academies of Sciences, Engineering, and Medicine. 2012. Long-Term Performance of Polymer Concrete for Bridge Decks. Washington, DC: The National Academies Press. doi: 10.17226/14623.
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6 CHAPTER TWO LITERATURE FINDINGS AND SPECIFICATIONS A review of the literature that pertains to TPOs is presented. Thin polymer overlays consist of a polymer binder and aggregates with a thickness not exceeding 25 mm (1 in.). USES OF THIN POLYMER OVERLAYS Harper (7) observed that “epoxy polymer overlays are not a ‘repair’ for bridge decks. They are only a means of protect- ing a deck that is in fairly good condition but is at risk for chloride and water penetration.” Based on the experience in Alberta, Carter (8) states that— 1. TPOs properly applied can provide service lives of up to 20 years, but that maintenance will be required if the surface is intended to remain free of defects. 2. TPOs can be used in high salt environments to extend the lives of existing bridges containing noncoated steel even if some corrosion has begun prior to repair. 3. TPOs are economically competitive with other repairs, especially when a minimum of repairs to the deck are required and a minimum of resin is used, that is, the overlay thickness is less than 10 mm (0.40 in.). 4. TPOs are more suited for preservation than for reha- bilitation. Resins are too expensive to be used on excessively rough or deteriorated concrete surfaces because considerable material would be required to bring the surface to grade. They can be used to extend the service lives of dense concrete overlays that are extensively cracked or to prevent freezing and thaw- ing damage to decks with inadequate entrained air void systems. 5. TPO installation requires specialized expertise. The primary failures observed in Alberta have been the result of workmanship or contractor-related errors. 6. Crack repairs are risky and are often a waste of money. Most nonworking, nonrepaired cracks will not reflect through TPO wearing surfaces within 5 years. Many working cracks will eventually reflect whether repaired or not. 7. Polymer wearing surfaces may lose toughness and ductility as they age under ultraviolet exposure. The 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 and abrasive wear. Sprinkel (4) states that the bridges that are the most likely candidates for TPOs (1) “are those that are in need of a skid- resistance wearing and protective surface but have peak- hour traffic volumes that are so high that it is not practical to close a lane to apply the surface except during off-peak traffic periods” and (2) “are those in which increases in dead load, reductions in overhead clearance, and modifications to joints and drains must be held to a minimum.” Multiple-Layer Overlays According to Sprinkel (4), multiple-layer overlays are best used on decks that have good ride quality because the over- lays follow the contours of the deck surface. This is the result of the layers being of uniform thickness, which results in the overlays following the surface irregularities instead of bringing the surface to a uniform grade. Slurry and Premixed Decks that have many surface irregularities are the best can- didates for slurry and premixed TPOs (4). PRE-OVERLAY EVALUATION The Missouri DOT performed an investigation of the cause of failures of the epoxy overlays that they had installed. Harper’s (7) observations related to failures involving TPOs are as follows: • Missouri recommends placing TPOs on decks that have less than 5% of the deck requiring repairs. It is impor- tant that decks be tested for delamination, chloride lev- els, and tensile strength of the concrete deck. Decks that require less than 5% of surface to be repaired have more likelihood of success. • Many of the failures appeared to be a failure of the top surface of the concrete deck instead of the polymer.

7 Examinations of spalled material usually showed a layer of concrete beneath the epoxy PC. • Decks that were rated higher before overlay placement performed better based on an inspection rating system for both the deck and overlay. • Longer span bridges were more likely to have problems with overlays owing to the greater deflections that can cause deck or overlay cracking. More flexible epoxies are recommended for longer spans. Bridges with girders that were wide flange sections or post-tensioned I-beams had overlays with higher ratings than bridges with plate girders. REPAIRS Cracks TPO contracts in Alberta in the period 1985 to 1987 required flexural cracks to be repaired (8). Flexural cracks were dis- tinguished from shrinkage cracks by (1) straightness in con- trast to shrinkage cracks, which tend to be more curved and randomly oriented; (2) location in negative moment region; and (3) presence of stains on the bottom of the bridge, which indicated that the cracks were full depth. The cracks were routed and filled with a flexible epoxy that was said to have “probably performed as designed until exposed to very low temperatures.” In 1988, “band-aid” repairs were developed. These repairs involved debonding the wearing surface along the crack, strengthening the wearing surface with tensile reinforcement centered over the crack. One repaired bridge originally had about 600 lineal meters (2,000 ft) of flexural cracks and 6,000 lineal meters of shrinkage cracks; after 4 years, about 100 lineal meters (325 ft) of cracks have reflected through the TPO. Another repaired bridge had 3,000 lineal meters (10,000 ft) of crack repairs, and about 70% of the cracks have reflected through the TPO. Carter concludes that, “the extreme cold, as well as the flexibility and live load deflection of this deck, make crack repairs appear futile” (8). Sprinkel (4) states that “large cracks should be filled ahead of time with a gravity fill polymer that is compatible with the overlay.” Concrete It is important that concrete with chloride ion content greater than 0.77 kg/m3 (1.3 lb/yd3) at the level of reinforcing be removed and replaced before placing the overlay (4). MATERIALS USED IN OVERLAYS Resins Typical resins are epoxy, polyester, and methacrylate (4). The curing time is a function of the type and amount of ini- tiator or curing agent, curing temperature, and binder con- tent. AASHTO Guide Specifications (6) show the minimum times for curing that have been successfully used for TPOs. White and Montani (9) point out the importance of ten- sile elongation and note that polymers that have good tensile elongation at room temperature may have poor elongation at low temperatures. They recommend 20% elongation of the polymer at 40°F and 30% when tested at 73°F in accordance with ASTM D638 (10). Gaul (11) reports on the use of epoxy asphalts over the previous 25 years. He describes the properties of epoxy asphalt and provides guidance on proper installation. Aggregates It is important that aggregates used in TPOs be dry (less than 0.2% moisture), angular-grained silica sand or basalt, and free from dirt, clay, asphalt, and other organic compounds. AASHTO Guide Specifications (6) give recommended gradings for multiple-layer, slurry, and premixed overlays. Fontana et al. (12) indicate that an increase in aggregate moisture to 1% by weight can significantly decrease the strength of the PC from which it is made. They state that the addition of 1% silane coupling agent by weight of the monomer (methyl methacrylate) can significantly offset up to 1% moisture in the coarse aggregate in the reductions in strength and freezing and thawing that normally would be expected. Polymer Concrete Application Rates Typical PC application rates for the three different types of overlays are given in AASHTO Guide Specifications (6). INSTALLATION Surface Preparation Surface preparation procedures need to be approved only when test patches, 0.3 m by 0.9 m (1 ft by 3 ft), constructed with approved materials are shown to have a minimum aver- age tensile rupture strength of three tests per patch, based on the procedure in ACI 503R (13), of 1.7 MPa (250 psi) (4). If the failure in the concrete occurs at depths greater than 6.4 mm (0.25 in.) and at stresses less than 1.0 MPa (150 psi), it is important that the concrete be removed and replaced with higher quality concrete, followed by surface preparation and placement and testing of new test patches. When stresses at failure occur between 1 MPa (150 psi) and 1.7 MPa (250 psi), the overlay can be placed, but the engineer determines whether part or the entire base concrete needs to be replaced. A visual inspection needs to be made before the overlays are

8 placed to ensure that the surface is properly prepared, dry, and free of dust or other contaminants. Substrate Tensile Strength The deck must have a minimum rupture strength of 1.0 MPa (150 psi) based on the test method in ACI 503R (13) or ASTM C1583 (14) to receive an overlay; otherwise, the con- crete must be removed and replaced so that a sound substrate is available to bond to the TPO (15). Repair of Substrate The substrate concrete needs to be patched, and large cracks [greater than 1 mm (0.04 in.)] in width need to be repaired (15). It is important that concrete with chloride ion content greater than 0.77 kg/m3 (1.3 lb/yd3) at the level of the rein- forcing steel be removed and replaced before placing the overlay (16, 17). Surface Cleaning “The surface should be cleaned by shot blasting (Figure 1) and other approved cleaning practices to remove asphaltic material, oils, dirt, rubber, curing compounds, paint, car- bonation, laitance, weak surface mortar, and other detrimen- tal materials that may interfere with the bonding or curing of the overlay” (15). Along edges of the deck and other areas that cannot be cleaned by shot blasting, grit blasting might be used. Test for Adequacy of Surface Preparation The test method described in ACI 503R (13) 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 prepara- tion to achieve a minimum tensile bond strength of 1.7 MPa (250 psi) or a failure area at a depth of 64 mm (0.25 in.) or more into the base concrete greater than 50% of the test area. The test result might be based on the average of three tests on an overlay test patch of at least 0.3 m by 0.9 m (1 ft by 3 ft). One test result could be obtained for each span or 418 m2 (500 yd2) of deck surface, whichever is the smaller area, as shown in Figure 2. The cleaning procedure could be approved if the test requirements are met for each test panel (6, 17). Because the temperature of the overlay can affect the test result in that adhesion decreases at higher temperatures, the temperature of the overlay at the time of the test should be recorded (17). FIGURE 2 Apparatus for performing pull-off test to evaluate surface preparation or overlay bond strength. Methods of Application It is important that TPOs be placed the same day that the surface is shot blasted to ensure cleanness. Areas of the deck FIGURE 1 Shot-blast preparation of the surface.

9 that are not shot blasted the same day could be shot blasted again just prior to installing the overlay (4). Multiple-Layer Overlays Multiple-layer overlays are constructed by application of the binder (resin or monomer system) to the deck surface by spray, squeegee, or broom and broadcasting gap-graded aggregate to excess over the fresh binder-covered surface (Figure 3). After the binder has cured, the loose aggregate is removed from the deck and a second layer is applied. The first layer consists of approximately 1.1 kg/m2 (2 lb/yd2) of binder and 5.4 kg/m2 (10 lb/yd2) of aggregate. The second layer consists of approximately 2.2 kg/m2 (4 lb/yd2) of binder and 7.6 kg/m2 (14 lb/yd2) of aggregate. The resin content is approximately 25% by weight of the overlay. The thickness is about 6.4 mm (0.25 in.) (15). FIGURE 3 Workers spraying resin followed by application of aggregates in multiple-layer TPO. Slurry Overlays Slurry overlays are constructed by applying a primer of monomer or resin system at an approximate rate of 0.41 kg/ m2 (0.75 lb/yd2) followed by a slurry mixture of about 2.6 kg/ m2 (5 lb/yd2) of binder, 3.8 kg/m2 (7 lb/yd2) of silica sand, and kg/m2 (5.21 lb/yd2) of silica flour. This slurry mix is applied with a gauge rake to ensure proper depth of place- ment (Figure 4). Gap-graded aggregate (as used in multiple- layer overlays) is broadcast onto the surface. A binder seal coat at 0.68 kg/m2 (1.25 lb/yd2) is applied. The binder con- tent is approximately 24% by weight of the overlay (primer and seal coat). The thickness is about 7.9 mm (0.31 in) (15). FIGURE 4 Using gauge rakes to control thickness of slurry overlay. (Courtesy: Virginia Center for Transportation Innovation and Research.) Premixed Overlays Premixed overlays are installed by mixing about 12% binder with the aggregates. A primer is usually applied to the sur- face at an approximate rate of 0.41 kg/m2 (0.75 lb/yd2) to improve the bond strength (Figure 5). The polymer concrete is placed and a vibratory screed is used to strike off and con- solidate the PC (Figure 6). In some applications, continuous batching and paving equipment has been successfully used to place premixed PC (Figure 7). A suitable skid resistance can be achieved by placing grooves in the fresh PC (Figure 8) or by broadcasting aggregates onto the fresh PC surface (Figure 9). The thickness is about 13 mm (0.50 in.) (15). FIGURE 5 Priming deck with initiated high-molecular-weight methacrylate prior to placement of PPC. (Courtesy: American Civil Constructors.)

10 a power screed, a manual screed, or a static screed. He gives examples of each in his paper. FIGURE 9 Equipment used to blow aggregates onto overlay surface. QUALITY CONTROL TESTS Quality control tests and required test results according to Sprinkel (15) are as follows: Resin It is important that resin or monomer be sampled at the rate of one sample for each 3,785 L (1,000 gal). The required vis- cosity, gel time, tensile elongation, and bond strength are shown in AASHTO Guide Specifications (6) along with the appropriate test method. Samples are to be accepted only when the required properties are furnished. The curing time is a function of the type and amount of initiator or curing agent, curing temperature, and binder content. AASHTO Guide Specifications (6) show the minimum times for cur- ing that have been successfully used for TPOs. Aggregate An aggregate sample needs to be obtained for each 43,350 kg (100,000 lb) of aggregate used. The aggregate grading can be determined to be acceptable when meeting the grad- ing shown in AASHTO Guide Specifications (6). Aggre- gates subject to wear would be silica or basalt and have a Mohs scale hardness of about 7. Typically, DOTs specify noncarbonate aggregates or define aggregates with a specified acid insoluble residue (AI) minimum that ranges from 80% to 95% for coarse aggregates for long-term surface friction. The test method for AI is pro- vided in ASTM D3042-09 Standard Test Method for Insoluble Residue in Carbonate Aggregates (19). This is the basis for all individual state DOT test methods. AASHTO does not have a listing for this test method. Some states, including Missouri, list New York State DOT Method 28 for AI. FIGURE 6 Vibrating screed consolidates and strikes off PPC overlay. (Courtesy: Virginia Center for Transportation Innovation and Research.) FIGURE 7 Metered mixing and placement of mixed polyester polymer concrete from mobile concrete batching plant. (Courtesy: Gomaco.) FIGURE 8 Placement and finishing fresh PPC surface with modified laydown machine and conventional tining rake. (Courtesy: Gomaco.) Dimmick (18) describes two methods of mixing and three methods for placing premixed TPOs. He suggests mixing in containers with electric power drills with paint paddle mix- ers or in drum mixers. For placement, he suggests the use of

11 Water Absorption White and Montani (9) recommend that the water absorption in PC be limited to a maximum of 1% by weight when tested in accordance with ASTM D570 (23). Abrasion White and Montani (9) recommend that overlays be tested at 125°F in accordance with ASTM D4060 (1,000 g load at 1,000 cycles) (24) and maintain a wear index of less than 2.0. Chloride Ion Penetration White and Montani (9) recommend that when tested in accordance with AASHTO T277-07 (25) the “polymer and system in place shall be required to register zero coulombs in the test to ensure chloride resistance.” The AASHTO Guide Specifications require that the permeability be a maximum of 100 coulombs at 28 days (6). Evaluation of Bridge Decks Carter (8) reports on the procedures used to evaluate many bridges. They were (1) ASTM C876 (26) for corrosion activ- ity using a 1.2-m (4-ft) square grid pattern; (2) air permeabil- ity on 75-mm (3-in.) cores that were oven dried for 24 hours. (specimens were pressurized from the bottom surface using the American Petroleum Institute Recommended Practices 40 test method); (3) bond strength tests using 75-mm (3-in.) cores taken randomly; (4) ultraviolet exposure tests using ASTM D638 (10) for measuring tensile strength and elonga- tion (samples were lightly sprayed with water each day); and (5) skid resistance tests done by a mobile skid trailer travel- ing at 64.4 km/h (40 mi/h). THIN POLYMER OVERLAY FIELD SECTIONS Many authors have reported results of TPO test sections, and some of the more significant tests are discussed in this section. 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) reports that a bridge deck in Ohio, constructed in 1962, had experienced transverse cracking and extensive wear. An epoxy TPO was selected primarily for the purpose of surface friction. The surface was shot blasted; because the pH exceeded 13, the surface was acid etched to reduce the pH to 9.2, although normally acid etching is not recommended for surface preparation. Cracks were not repaired. The sur- face was primed with neat epoxy. Polymer concrete consist- Polymer Concrete Specimens made from the furnished resin and aggregate need to be made and tested in accordance with the tests shown in AASHTO Guide Specifications (6). The test results should meet the minimum requirements in the table for the type of polymer used. Gel Time The gel time needs to be monitored to ensure that the require- ments of AASHTO Guide Specifications (6) are met. Application Rates The application rates need to be monitored to ensure that they are in conformance with AASHTO Guide Specifications (6). Curing The minimum curing time before opening to traffic is given in AASHTO Guide Specifications (6); however, a compres- sive strength of 6.9 MPa (1,000 psi) based on field-cured cubes (ASTM C579, Method B) (20) might be obtained before opening to traffic (6). TEST METHODS Shrinkage Many monomers and resins shrink during curing, particu- larly polyester-styrene and acrylics. Zalatimo (21) and Zala- timo and Fowler (22) developed a test method for measuring shrinkage, including the effect of relaxation. A 150-mm × 150-mm × 0.9-m (6-in. × 6-in. × 36-in.) beam is overlaid with the PC with the center portion unbonded to the concrete substrate by means of plastic sheets placed on the concrete surface. A measuring device with a 250-mm (10-in.) gauge length is placed into the fresh PC; at different times after the PC has initially cured, one end of the unbonded sec- tion is cut. Residual shrinkage stresses in the PC will cause the unbonded section to contract from the cut end. It has been shown that when the time of cutting is increased, the measured shrinkage is reduced. For most materials tested, including epoxies, polyester-urethane, and polyester-sty- rene, the shrinkage is generally nonexistent after 72 h, which indicates that relaxation has occurred. Tensile Elongation White and Montani (9) recommend that cured resins have a minimum of 20% elongation at 40°F and 30% when tested at 73°F in accordance with ASTM D638. The AASHTO Guide Specifications have the requirement of 30% to 80% tensile elongation for epoxy and polyesters (6).

12 In 1971, 16 test sections using different resins and aggre- gates were installed. Epoxy asphalt and a combination of hard metagraywacke and soft, lightweight, synthetic aggregate were selected for the overlay. In 1976 and 1977, the upper and lower decks were resurfaced with 256 m2 (2,760 ft2) of 19-mm-thick (0.75-in.-thick) epoxy asphalt using conventional asphalt paving machines followed by compaction with rubber tired and steel drum rollers. In 1996, an inspection showed five types of distress: (1) small mechanical gouging depressions, (2) three locations of fire pitting owing to vehicular fires, (3) pot holes resulting from delamination of the lightweight concrete substrate or weak bond to the epoxy coal tar chip seal (approximately 93 m2 or 1,000 ft2), (4) joint crumbling that required six joints to be repaired, and (5) reduced skid resistance that had not been predicted by lab tests. Bond pull-off tests using ACI 503R-93 (13) with 50-mm (2-in.) diameter cores gave ten- sile bond strengths ranging from 0.84 to 2.45 MPa (122 to 356 psi). The performance was deemed a success for the 20-year life for a bridge experiencing 250,000 vehicles per day in both directions. Gaul (11) gives a 25-year history of the use of epoxy asphalt, including properties, manufacture, methods of use, and list of applications. Alberta Overlays Initial Investigation In an initial investigation, Carter (8) states that Alberta had waterproofed 66 bridges with TPOs. Many of the TPOs were placed on dense concrete overlays that were heavily cracked owing to long-term drying shrinkage. The cracks appeared to propagate each year when subjected to vehicle loads in cold weather. Half-cell (copper sulfate electrode) and chloride content testing were performed on many of the decks, and it was concluded that corrosion was continuing to develop and would likely reduce the service life and require a second major rehabilitation. 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. Test Bridge In 1984, a test bridge was selected and divided into eight equal sections of 139.4 m2 (500 ft2) to test some of the avail- able membrane wearing surface systems, including some parking garage membrane systems. These softer, more flex- ible materials performed poorly on the bridge. One system composed of coal tar epoxy was seeded with a very hard (Mohs hardness of 9) brittle slag aggregate. The aggregate ing of silica sand and 10.5 (wt %) epoxy resin was batched in mixers and placed to a depth of 6 mm (0.25 in.). The sur- face was finished with a wood screed to provide transverse irregular ridges. The area overlaid was 1,642 m2 (17,676 ft2). After 10 years and 121 million vehicles, the surface was said to still have excellent anti-skid properties. About 2 m2 (22 ft2) of overlay had to be replaced because of delamination; it was not known whether the delamination occurred in the substrate or at the bond line. Post-Tensioned Parking Garage Post-tensioned slabs in a 6-year-old parking garage in Ten- nessee had experienced severe freezing and thawing as a result of an improper air void system (27). Tests on cores indicated concrete compressive strength of about 6,000 psi. Some deformed bars and post-tensioning tendons were cor- roded and exposed. The chloride ion content at a 12-mm (0.5-in.) depth was three times the corrosion threshold level of 0.77 kg/m3 (1.3 lb/yd3). Methyl methacrylate (MMA) PC was selected because of (1) the ability to place it in very thin applications, (2) the ability to place the material in a range of −7°C (20°F) to 38°C (100°F), and (3) short cure time that allowed the garage to remain open during repairs. The dete- riorated concrete was chipped out and the corroded bars and tendons were exposed. The surface was sandblasted and then primed with MMA primer. Deep spalls were filled with MMA PC that used pea gravel. All of the negative moment regions received a 6-mm-thick (0.25-in.-thick) MMA PC overlay. Inspections were made at 1.5, 7, 10, and 13 years after repair. During the first inspection, very shallow 0.3- mm (0.012-in.) deep crazing cracks were observed in areas exposed to sunlight and were attributed to the trowel finish- ing that brought excess monomer to the surface, resulting in additional shrinkage. No spalling, cracking, or delami- nation was observed until the last inspection; at that time, some delamination associated with cracking in the surface was observed. Cracks over deformed bars and tendons were associated with continued corrosion of the bars and tendons. Apparently, all of the contaminated concrete around bars and tendons had not been removed and corrosion had con- tinued at a slow rate. In areas where freezing and thawing had occurred and corrosion had not continued, the overlay performed well. Epoxy Asphalt TPOs The San Francisco–Oakland Bay Bridge was constructed in 1936, and ceramic tile embedded in mortar was used as permanent lane striping (11). In 1963 and 1964, the upper and lower decks were resurfaced to cover the ceramic tile striping with a PC made of coal tar epoxy binder and quartz beach sand. The binder was sprayed on the surface and the sand was broadcast onto the binder. By 1968, the sand had begun to polish and to be picked out, reducing the skid resistance, although the binder was in excellent condition.

13 disintegrated under tire impact, leaving tiny holes in the membrane. After 6 years, most of the membrane had worn away. Two other sections using silica sand embedded in epoxy resins became highly polished because of the poor wear resistance of the sand. One of these systems exhibited some debonding that was attributed to the well-graded fine aggregate creating a brittle epoxy–aggregate composite material that performed differently than the deck when sub- jected to live load and thermal stresses. The most durable of the eight systems was a flexible epoxy that used a poorly graded basalt aggregate with a relatively high aluminum oxide content. It had the highest bond strength and the best electrical resistivity readings. Description of TPOs The TPOs applied after 1985 usually consisted of two lay- ers plus a tie coat, resulting in an average thickness of 6 mm (0.25 in.) (8). No primer was used. Each layer consisted of liquid seeded with aggregate applied with squeegees and rollers to seal the deck surface. Excess aggregate was removed after the resin hardened. The tie coat consisted of a thin layer of resin used to seal pinholes and voids in the composite layer. In 1988, six bridges with low traffic volume were repaired with a less expensive system that had only one seeded layer applied on a nonseeded primer. Permeability tests indicated better waterproofing than the system with two seeded layers and no primer (8). In 1989, the two-layer system was changed by applying the tie coat first as a primer, followed by the two seeded lay- ers. Three bridges were repaired by using a premixed PC that was screeded; the main advantage is the speed at which they can be placed on large bridges, resulting in labor sav- ings and reduced closure time. A possible disadvantage is the possibility of entrapped air at the bond line, which would reduce bond strength (8). Performance of 21 Bridges Carter (8) reports on 21 TPOs of a total of more than 100 that had been placed in Alberta beginning in the 1960s. Typi- cally, 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 devel- oped numerous cracks. Many of the bridges, especially the ones with the largest spans, had steel superstructures that were more flexible and developed more cracking and also received more deicing salt than the average deck. In 1990, the accumulated damage to the TPOs was 0.6% of the total 22,052 m2 (237,000 ft2) installed on the 21 bridge decks between 1985 and 1987. By 1995, the failed surface area had increased to 2.0% at an average of 9 years. The original installation had a 5-year warranty, so that at an age of 5 years the contractor had repaired all of the original defects. The amount of defective surface area in 1995 included the total distress that had been repaired before and after the 5-year warranty repairs. Thermal Incompatibility One bridge that was overlaid in 1991 experienced 10% debonding in 2 years and 50% in 3 years (8). The failure involved shear failure of the dense concrete just below the bond line. The thickness was 15 mm, greater than normal; that also leads to increased stress owing to thermal changes. The initial strength of the polymer (the type of polymer was not given) was 25 MPa (3,600 psi), which was considerably higher than for other “well-performing resins that had been used in Alberta.” The strength increased to 30 MPa (4,350 psi) when exposed to ultraviolet light. The tensile elongation of the polymer was found to have decreased significantly from its original 30%. It was concluded that thermal incom- patibility with the substrate caused the failure because of loss of flexibility. Aggregate A bridge placed in 1990 used red basaltic aggregate on one side of the bridge and green trap rock on the other side (8). After 2 years, it was observed that more red aggregate was accumulating in the gutter lines of the deck than green aggregate. Further testing using cores indicated that five times as many empty sockets were left by red aggregate. The problem was attributed to the fact that the red aggregate was more rounded and had a lower fracture-face count. In addi- tion, after 5 years of service, the amount of lost or debonded overlay was twice as much on the red side even though the overlays were placed at the same time by the same contrac- tor. A study of other bridges that used the red, green, and a less frequently used black aggregate was conducted. It was found that under similar conditions of age and traffic, the red overlays were debonding 25 times more rapidly than the black overlays and 19 times more rapidly than the green ones. Stress–strain tests on cylinders using the same polymer and the three different aggregates showed that the polymer con- crete made with the red aggregate could absorb only 70% as much energy (area under the stress–strain curve) than the other materials (8). Contractor Experience A study of 71 bridges for durability also evaluated the per- formance of contractors (8). The overlays constructed by the most experienced TPO contractors (i.e., those who had done the most work) were significantly more durable than those constructed by contractors with lesser amounts of installa- tion experience.

14 tic chip coats over aging TPOs to renew their skid resistance and to extend the life of the overlay (8). Carter reported that 56 bridges have been treated using inexpensive chip coats; the results were satisfactory. Virginia Multiple-Layer Overlays Virginia has used many TPOs over the years, and Sprinkel (16) reported on 18 multiple-layer overlays and one single- layer overlay placed between 1981 and 1987. The binders for the multiple-layer overlays included four polyester-styrenes, one polyester amide alkyd, one MMA, three EP5-LV epox- ies, and two flexible epoxies. A single-layer high-molecular- weight methacrylate overlay was installed. After all major spalls were repaired, the bridge decks were shot blasted, except cleaning with compressed air was used in the high- molecular-weight methacrylate single-layer overlay. The ini- tiated and promoted resins were sprayed or broomed onto the clean surface, and before the resin gelled, aggregate was broadcast onto the surface. After curing, the excess sand was broomed or vacuumed off the surface. The additional layer or layers were applied in a similar manner. Three or four lay- ers were applied for the polyesters; the epoxy overlays used only two layers. The high-molecular-weight methacrylate overlay had only one layer. The aggregate was clean, dry, angular silica sand. Tensile Bond Strength Virginia requires a tensile bond strength test, based on ACI 503R (13) or ASTM C1583 (14), to ensure that the instal- lation procedure would give the target strength of 1.7 MPa (250 psi) or more. The contractor was required to install two layers of an overlay, 0.3 m by 0.9 m (1 ft by 3 ft), on each span or 167 m2 (200 yd2), whichever was the smaller area. Their experience indicated that a typical standard deviation was 0.27 MPa (40 psi), and average bond strength of 1.52 MPa (220 psi) was required for satisfactory performance. The tensile bond strengths were found to decrease with time. Initially, failures were in the concrete substrate, but with time the failures were in adhesion or near the bond line. In bridges on which traffic was allowed on the shot-blasted surface before overlay application, the initial bond strengths were low (16). Shear Bond Strength Guillotine shear strength tests were performed on cores taken from the bridge decks (16). Some cores were thermally cycled from −18°C to 38°C (0° to 100°F) three times each day. For some overlays, the thermal cycling gave good cor- relation with tensile bond strength test results from the field. It was concluded that environment had a greater effect on the bond strength for polyesters than for the epoxies, and that degradation of bond strength with time leads to delamina- tion for some overlays within 10 years. Ability of TPOs to Protect Nondurable Concrete TPOs were applied to several bridges with concrete decks of substandard quality and durability based on Carter’s experience (8). One bridge deck had little entrained air, and the surface was badly scaled on one side after one winter of service. Another bridge had a wavy surface owing to hand screeding, and the cover over the steel varied “sub- stantially.” The bridge carried heavy traffic, received heavy applications of deicing salt, and had many freezing and thawing cycles. A third bridge had a 1972 overlay that had been placed with the expectation of providing 10 to 15 years of life. By 1986, the overlay was partially debonded and had moderate salt scaling. A single-layer TPO was placed with the goal of providing 10 years of service life. It was concluded that “the extension of deck service life result- ing 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 sig- nificantly reduced when a significant amount of reflective cracking was present in the concrete. “Apparently, since the polymer overlays did not effectively seal the wide, moving cracks, deck deterioration proceeded below the overlay in the cracked areas.” Effectiveness in Sealing Deck Cracks Carter (8) notes that it is difficult to know which cracks are reflective cracks prior to installation of TPOs, and that it may be better to install the overlay and then repair the cracks later. In his opinion, even when crack repairs are made, they may last only 5 to 10 years, but the life of the overlay is likely to be 15 to 20 years (8). One bridge had about 1,500 m (5,000 ft) of cracks in 1985 before installing the overlay. About 185 m (600 ft) of “apparently actively moving cracks” were repaired by routing and using an epoxy caulking mate- rial. After 5 years, approximately 46 m (150 ft) of cracks had reflected through the overlay; after 10 years, it had increased to 215 m (700 ft). It was thought that ultraviolet radiation had caused the polymer to lose flexibility over time. Thickness of TPOs in Cold Climates Carter (8) notes that TPOs are more durable in Alberta when they are thin. The reduction in temperature [to as low as –40°C (–40°F)] causes the polymer to become more brittle at the same time that interfacial stresses are developing. The stress is proportional to the thickness of the polymer. Exces- sive thickness can lead to bond failures. Repair of TPOs Because the service life of TPOs is affected by ultraviolet radiation and traffic wear, Alberta began placing thin asphal-

15 tiple layer, slurry, and premixed overlays is given; proper- ties of epoxy, polyester, and methacrylate binders and PC are presented with the appropriate test method for each prop- erty; and typical polymer concrete application rates for the three types of application methods are given. The 14 bridges were evaluated in 1991 and 1995. Three overlays, each constructed with multiple-layer epoxy, multi- ple-layer epoxy urethane, premixed polyester, and methac- rylate slurry, and two overlays installed with multiple-layer polyester, were included in the evaluation. The overlays ranged in age from 6 to 19 years. Tensile Bond Strength The tensile bond test was a modified version of Virginia Test Method 92. This method is similar to ACI 503R (13) but dif- fers 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) for the multiple-layer epoxy, multiple-layer epoxy urethane, and the premixed polyester over the life of the overlays; the multiple-layer polyester overlays had lost considerable bond strength [from over 2.0 MPa (300 psi) to about 0.50 MPa (75 psi)] and were projected to fail within 10 years. There were insufficient data to evalu- ate the MMA slurry overlays (15). Permeability Permeability performance based on AASHTO T277-07 (25) tests in 1995 and from a previous project was given. The results indicated that the lowest permeability (<100 cou- lombs) was provided by the methacrylate slurry, and that negligible to very low permeability (<1,000 coulombs) was associated with the multiple-layer epoxy and epoxy ure- thane and the premixed polyester. Multiple-layer polyester had greater increases in permeability but was predicted to provide good protection for 10 years (15). Skid Resistance Based on ASTM E524 (29) (smooth tire), acceptable skid numbers (<33 coulombs) were being maintained for all over- lays except MMA slurries, which were showing a downward trend (15). Durability Polymer concrete was tested for freezing and thawing in accordance with ASTM C666, Procedure A (30); modifi- cation by the addition of 2% sodium chloride to the water had shown a durability factor of over 90% after 300 cycles, considerably greater than the minimum factor of 60% generally accepted for concrete. Polymer concrete had good resistance to wear. Projections based on tensile bond Rapid Chloride Permeability All polyester and epoxy overlays displayed very low (100 to 1,000 coulombs) or negligible (<100 coulombs) permeabil- ity initially; the high-molecular-weight methacrylate overlay displayed low permeability (1,000 to 2,000 coulombs). After 1 year, the brittle polyester had a moderate permeability (2,000 to 4,000 coulombs). After 4 years, the stiffer epoxy had the lowest permeability, and after 5 years, the flexible had the lowest, both being in the very low category. After 100 thermal cycles in the laboratory, only the brittle polyes- ter and the epoxies had a negligible permeability; the MMA, high molecular weight, and some of the other polyesters had low or moderate values (16) Electrical Resistivity Electrical resistivity tests (28) were performed to deter- mine the presence and extent of microcracks. Only the flex- ible polyester had no significant cracks until 3 years after placement; all others had extensive cracking after 1 year or less. However, the permeability tests indicated that the other overlays were “providing significant protection against chlo- ride penetration” (16). Half-Cell Potential Copper sulfate half-cell potential readings (26) indicated that only four small areas on four spans had a 90% corrosion probability. Over a 6-year period, the half-cell readings did not change significantly (16). Skid Resistance All overlays had adequate skid resistance at the time the overlays were installed, and the values are reported in Sprinkle (16). The overlays made with the more rigid epoxy showed a significant reduction in skid resistance after 1 year of service; the reduction was because these overlays used less resin and finer sand than the other overlays in the pro- gram. Virginia no longer uses this epoxy (16). Wear The most wear occurred in the travel lanes. The greatest wear occurred for the brittle polyester-styrene (2.5 mm or 0.10 in. in 5 years), but that rate is 23% of the wear reported for latex-modified concrete. The conclusion was that the overlays would likely delaminate or exhibit an unacceptable skid resistance before the overlays wear through (16). Nineteen-Year Performance Sprinkel (15) provides a summary of performance of TPOs on bridge decks in California, Michigan, Ohio, Virginia, and Washington. A summary of aggregate gradations for mul-

16 (8,000 psi) and a tensile elongation of 5%. The surface was shot blasted and primed with either high-molecular-weight methacrylate or an unsaturated diaromatic glycol fumer- ate. The aggregate was 12 mm (0.5 in.), with less than 25% crushed particles. The overlay was installed using a contin- uous screw-type mixer and a paving machine. Dry screen- ings were broadcast on the surface to provide improved skid resistance. The overlay was 3.6 mi in length and had a 19-mm (0.75-in.) thickness. Krauss (33) states that, “Over 25 bridge decks have been overlaid with polyester-styrene concrete overlays and all the overlays are performing well.” He states that in 1988 there had been no delamina- tion on any polyester-styrene concrete overlay placed by contract. No overlay since 1983 had shown signs of wear or cracking. Several Epoxy TPOs Two epoxy overlay test sections were reported by Dimmick (34). Toll Booth Lanes Portland cement and epoxy polymer concrete were tested side by side at toll booth lanes into Newark Airport in 1977. The portland cement had about 40 MPa (6,000) psi compres- sive strength. The epoxy concrete had 14% epoxy by weight. The surface was primed and the hand-mixed epoxy concrete was placed on portland cement concrete slabs to a depth of 0.16 mm (0.625 in.) in the wheel paths. After 6 years, the portland cement concrete was badly worn to a depth of 13 to 19 mm (0.5 to 0.75 in.) and had about 1 m2 (10 ft2) of deeper spalling. The portland cement concrete wore out after about 97 million vehicle passes. The epoxy polymer concrete had no surface defects and still had an excellent textured surface. After 15 years, the epoxy polymer concrete was still pro- viding excellent skid resistance and had shown about 3-mm (0.12-in.) wear after 243 million vehicular passes. One small patch had to made, and a small gouge had occurred in the surface about 12 mm (0.5 in.) deep. Bridge Deck Overlays for Skid Resistance In 1983, the Ohio DOT found it necessary to overlay three bridges to obtain improved skid resistance during times of rain, snow, and ice. The substrate had transverse structural cracks, which exhibited spalling and grooves that were com- pletely worn down in many places. The surface was shot blasted, the epoxy polymer concrete was mixed in drum mixers, and it was placed on a surface primed with neat epoxy to an average depth of 6 mm (0.25 in.). It was finished with a wood screed to provide good texture. The total area of overlay placed was 1,637 m2 (17,676 ft2). After 10 years, 120.8 million vehicles had passed over the overlay. It still had excellent skid resistance. Only 0.09 m2 (1 ft2) has had to be replaced; the cause of failure was unknown. strengths, permeability, and skid resistance, for the over- lays, with the exception of the MMA slurry and multiple- layer polyester overlays, indicated a service life of at least 20 years (15). Epoxy TPO Overlays The advantages of epoxy TPOs were given, including excel- lent bond strength, unaffected by alkalinity of concrete, little shrinkage, low modulus, high strength-to-weight ratio, and not flammable. Epoxy PC consists of resin, hardener, and aggregates. Nabar and Mendis (31) provide a list of key proj- ects 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 pro- cedures, service life, trouble-shooting procedures, and loss of skid resistance. Evaluation results of four bridges in Michigan, Ohio, Vir- ginia, and Washington are given. Fort Worth, Texas, Overlays Zalatimo and Fowler (22) report on different resins used to construct small overlay test sections on two bridges in Fort Worth, Texas. One bridge used (1) high-molecular-weight methacrylate, (2) four hybrid polyester-urethanes (three low modulus and one high modulus), (3) experimental epoxy with a high modulus, and (4) two commercially available epoxies. The PC was batch mixed and placed in a 12-mm (0.5-in.) thickness with a vibrating screed. Additional aggre- gate was broadcast on the surface to obtain improved skid resistance. The second bridge used two polyester-urethanes, experimental polyester, and an experimental epoxy, which were applied as multiple-layer overlays over a high-molec- ular-weight methacrylate primer. Two layers were applied, resulting in a thickness of about 9 mm (0.375 in.). The over- lays generally performed well, except that two of the hybrid resin overlays failed owing to the primer being allowed to pond and form a thick layer. Because of thermal stresses, it failed within the first couple of months. The 5-year evalua- tion found that most were in good condition, although some had polished on the surface owing to inadequate aggregate seeding for texture. California I-80 Maass (32) reports that the Donner Pass section of I-80 in California that was overlaid in 1986 has performed well. In 1983, the section of highway carried an average daily traf- fic of 9,750 vehicles, of which 950 were trucks. The average annual rainfall is 1.54 m (61 in.) and the average snowfall is 10.4 m (410 in.). Two resins were used—one with a ten- sile strength of 17 MPa (2,500 psi) and a tensile elongation of 35%, and another that had a tensile strength of 55 MPa

17 Washington Overlays Three epoxy and two MMA TPOs were installed and moni- tored. For all overlays, the decks were shot blasted prior to placing the overlays. The epoxy overlays were placed using an epoxy primer, then a coat of epoxy followed by an application of aggregate. After curing, the excess aggregate was removed and an epoxy seal coat was applied. The MMA overlays used an MMA primer and a slurry application of MMA and aggre- gate with the thickness controlled using gauge rakes. Addi- tional aggregate was broadcast on the surface. The results of the 10-year monitoring were reported in 1995 (35). Tensile Bond Strength The average initial tensile bond strength was 2 MPa (297 psi) for the epoxies, which was greater than the 1.72 MPa (250 psi) specified. The average for the MMA was only 1.45 MPa (211 psi). After 1 to 5 years of age for the overlays, follow-up testing was performed. For the epoxies, the average strength had reduced slightly to 1.89 MPa (274 psi), but for the MMA the strength had reduced to 0.98 MPa (143 psi). Frictional Resistance For epoxies, the initial average skid number was 70 but reduced to 20 after 7 years. For the MMA, the initial aver- age reading was 40, and it reduced only slightly to 39 after 9 years. Chloride Ion The average permeability to chloride ion as measured by AASHTO T277-07 (25) was 0 for the MMA overlays and 3 coulombs for the epoxy overlays. New York In 1993, New York DOT performed a study of overlays that involved a survey of other states and an evaluation of its own TPOs that were 5 to 7 years old. It had placed three different resin systems: polyester, MMA, and flex- ible epoxy. New York DOT concluded that the newer resin systems “support optimism to suitability and durability.” It was further concluded that the overlays in the state appear to meet expectations. New York DOT recommended the use of TPOs for only two applications: (1) for bridges where weight was critical such as moveable spans and (2) bridges for which extended delays would be intolerable, such as in urban areas (36). Since 1999, New York DOT has installed 44 TPOs (37). Thirty-eight were epoxy, and one each was MMA, polyurea, polyester, polyurethane, and vinyl ester. One was not identi- fied as to the resin type. The total area of bridges overlaid was 18,832 m2 (202,632 ft2). In 2007, the Materials Bureau evaluated 15 of the TPOs. Among the findings were • The MMA overlay was the only one of the 15 to have failed. It had several spalls with about 90% of the over- lay remaining and 80% to 90% of the friction aggre- gates intact. • The polyester overlay was in very good condition, with some polishing observed. • The urethane overlay was in excellent condition. • 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 con- dition, 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. It has experimented with using one-coat overlays instead of two, sandblasting in place of shot blasting, and using boiler slag instead of the normally specified aggregates. Alabama Alabama placed four 6-mm (0.25-in.) polyurethane, twelve 9-mm (0.375-in.) polyester, two 19-mm (0.75-in.) low- modulus epoxy, and one 12- to 19-mm (0.5- to 0.75-in.) asphaltic-based Novachip overlays. The performance of the polyurethane was poor, the polyester was variable, the low- modulus epoxy was excellent after 8 years, and the Novachip was excellent after 3 years. Montana Four different overlays were installed on 13 bridges in Mon- tana; two portland cement concrete, one acrylic modified concrete, and a low-modulus epoxy. On a single bridge, an MMA overlay was installed. Both the epoxy and the MMA exhibited limited cracking but no significant delamination or dramatic loss of surface roughness after 2 years. The evaluation period was not long enough to make a thorough assessment. Louisiana Four different epoxy TPOs were applied to a bridge in Louisiana in 1985 to evaluate their performance as fric- tion surfaces primarily and as sealers secondarily. After

18 found to have chloride in excess of 11 lb/yd3, and the pur- pose of the overlay was to provide additional protection. The popularity of the TPOs has resulted from the lower cost of the installation and traffic control because of much shorter periods of lane closures than for bonded cement overlays. Typically, for a silica fume overlay, the structure is closed overnight for 20 days and requires that temporary traffic signals be installed; in comparison, the TPO requires flaggers for only 5 days and is open overnight (31). LaGuardia Airport, New York The two runways at LaGuardia Airport in New York were constructed more than 30 years ago. Texture had been main- tained by cutting grooves in the concrete surface. But even- tually, it was found to be structurally unacceptable to cut away more of the section to reestablish the grooves. It was decided to place a TPO because of its projected service life and the reduced time required to place the overlay and return the runways to service. The two runways accommodate more than 1,400 aircraft daily. 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. The slurry method consisted of mixing the aggregate and resin and placing the slurry in one operation. The broom- and-seed method consisted of placing a layer of resin and then broadcasting aggregate having a nominal size of 1/8 in. into the resin. Four applications were placed to obtain the required ½-in. overlay. Based on the test sections, the epoxy resin applied by the broom-and-seed method was selected. Visual inspection showed the epoxy slurry method and the MMA test sections did not have a uniform surface texture, with some areas having a glassy appearance. The broom- and-seed method provided a uniform surface with excellent frictional resistance. The repair work was initiated and represented the first major runways to be overlaid with an epoxy TPO. The work was performed between 6 a.m. Saturday and 6 a.m. Monday, weather permitting. The surface was shot blasted to produce minimum bond strength of 200 psi, and bond tests were per- formed every weekend before application of resin to confirm that the substrate had adequate bond strength to achieve the specified strength. Bond tests were performed by bonding 100-mm × 100-mm (4-in. × 4-in.) steel plates to the concrete surface and pulling in direct tension in accordance with ACI 503R (13). The overlay was constructed by applying four applications of epoxy resin and aggregate. Prior to opening the runways to traffic, bond tests were performed to determine whether the specified bond strength of 1.4 MPa (200 psi) was met. The specified strength was met every weekend after 9 hours of cure time. The bond 5 years, an evaluation showed the surface friction as mea- sured by the British Portable Tester and ASTM E274 (38) skid trailer to be very good for two of the epoxies and less effective for the others. All remained bonded and resisted cracking (17). Kansas The Kansas Department of Transportation (KDOT) placed its first overlays in 1999. Four contractors placed approxi- mately 100 linear feet (333 yd2) each on the same bridge. The four materials, all epoxies, had similar properties. The bridge deck was shot blasted using International Concrete Repair Institute (ICRI) Concrete Surface Preparation (CSP) Standards 5 to 7 for the desired texture. Flint rock was used for the aggregate. In 2000, bond failure occurred in all four sections of overlays. The failure was determined to be caused by the presence of a bond breaker (said to be a byproduct of alcohol production) on the original concrete. Saw cuts were made outside the delaminated areas, and the contaminated concrete was removed by sandblasting and chipping. The overlays were replaced with the same materials and same procedures as used initially. After 9 years and approximately 21,000,000 vehicles, with 30% heavy trucks, no problems have been experienced. The skid coefficient was found to be 53 using a ribbed tire in 2003. KDOT has placed more than 100 TPOs with the goal of minimizing water and chloride intrusion to preserve the structures. (In addition to the overlays placed by KDOT, four counties have placed 13 TPOs.) Some structures have had minimal spalling, which was repaired. Many have had delaminated silica fume or high-density concrete overlays, and because the surface had not failed, the decks were shot blasted before placing the TPOs. Where shallow delamina- tions had occurred, the loose concrete was removed, the area repaired, the entire deck was shot blasted, and the TPO placed. The intent of KDOT is to place the overlays on decks that are not seriously deteriorated to preserve the structure. TPOs on three new bridge decks have been installed for different construction errors. One deck had concrete that exhibited high permeability and low density because of concrete consistency problems. Another had reduced cover because of a malfunction of the screed. A third had been con- structed with a corrosion-inhibiting admixture, and exten- sive cracking in the deck occurred. The TPO was placed to seal the cracks. The first two bridges had TPOs applied using 50% greater amounts of epoxy than the normal overlay. The third used a standard two-coat system. One new bridge was designed for a TPO to be applied before opening to traffic. The bridge is on a service road heavily trafficked by trucks hauling sand and salt and trucks accessing a KDOT shop. The previous bridge deck was

19 FAILURES Alberta Lessons Learned from Failures Carter (8) provides observations on lessons learned from TPOs installed in Alberta, but states that his comments may not always be in agreement with experiences in other areas. 1. Failures are usually the result of constructability rather than materials. If the in-place material is defec- tive, it is usually because of improper proportioning or mixing. Using different colors for multicomponent systems would help reduce proportioning errors. 2. The moisture content of the deck is important in achieving good bond strength of the TPO to the deck. Some parts of the deck, including low areas, other areas that drain slowly, and gutters, dry slower owing to ponding. The moisture may prevent adequate bond strength development. 3. Deck repair patches made with portland cement con- crete need to be wet cured to reduce shrinkage and subsequent debonding. The patches should be allowed to dry sufficiently to achieve good bond to the TPO. In Alberta, the maximum depth for mortar patches is 15 mm (0.67 in.) because deeper patches may develop cracks around the perimeter at low temperatures. 4. The more the surface is prepared and roughened, the greater the bond strength will be. Shot blasting pro- vides a more uniformly prepared surface than does sandblasting. 5. In cold climates, thicker TPOs will fail faster than thinner ones because of the different thermal coef- ficients of expansion of the concrete and the PC. 6. Thin TPOs cannot be expected to provide a smooth surface on a rough deck surface. Deck patching must be done carefully to prevent the creation of a rough surface. Bumps in the surface of the TPO will shorten the life, particularly when snowplows are used. 7. Aggregate type and grading are important for wear resistance, flexibility, toughness, and crack-bridging ability of the wearing surface, particularly when high-modulus polymers are involved. 8. The method of seeding aggregate into the resin is important in preventing surface ripples, wicking, strengths averaged 1.8 MPa (270 psi) for deck surface prep- aration and 2.6 MPa (390 psi) for the overlay bond strength for the project. The Port Authority modified its contract requirements and bidding procedures in order to obtain the best possible wearing surface. Epoxy resins were tested for conformance to specifications prior to soliciting bids. Four resin suppli- ers were approved with no substitutions. The resin suppliers were then formally requested to select a contractor that could provide a joint warranty with them. The warranty required the contractor to repair any defects within 5 years of instal- lation. The resin supplier was required to have a full-time representative on the site when work was being done. The purpose for the contract requirements was to provide the contractor and material supplier the incentive to take joint responsibility for the installation. The contract required the finish surface to have a mini- mum surface friction number of 60 as determined by the British Pendulum Tester. The average friction number obtained for the project was 71. Grooves 6 mm × 6 mm (¼ in. × ¼ in.) were cut 37 mm (1.5 in.) apart, center to center, in the transverse direction several days after the overlays were placed. No complaints have been received from airlines for excessive rubber wear on tires. The overlays were completed for one runway in 1998 and the other in 1999. The overlays have performed well, with only minor repairs required. Most of the delamina- tions occurred at structural expansion joints and at locations where the overlay was very thick, about 1 in. The airport management and the airlines have been pleased with the per- formance of the overlays (39). Pennsylvania Pennsylvania DOT installed three TPOs: premixed polyes- ter, an epoxy multiple layer, and an epoxy urethane mul- tiple layer, each on two separate bridge decks. The decks were rehabilitated after being evaluated for chloride ion content, corrosion activity using half-cell tests, and delami- nation using chain drag. Problems were encountered dur- ing construction with the premixed polyester resulting in a resin-rich mixture that made it susceptible to oxidation and ultraviolet light degradation. A 5-year evaluation indicated significant moderate spalling, cracking, and debonding in the polyester overlay. The two epoxy multiple-layer overlays provided good long-term performance as evidenced by the excellent protection against chloride and moisture intrusion. As a result of the performance, the use of epoxy and epoxy urethane multiple-layer TPOs was recommended for future use by Pennsylvania DOT (39).

20 high porosity, and resin-rich areas that are not ther- mally compatible with the concrete. It is important that the aggregate be allowed to spread out and fall downward into the resin, with the dust and fines car- ried off in the air. In hot weather, it is important that aggregate not be introduced too quickly; rather, it needs to be slowly and evenly built up on the surface until no wet spots are visible. 9. Static mixers and paddle mixers are not foolproof. The viscosity of the resin components are affected by temperature and hot or cold weather may affect the mixing process. Routine calibration checks must be made. Case History of a Failure Carter (8) reports that a bridge overlaid in 1985 had many problems even though only experienced contractors were allowed to bid for the job. The contractor provided a 5-year warranty, but problems occurred quickly. The surface prepa- ration by the contractor was rejected twice; the final sur- face preparation was a compromise. The contractor did not notify the resin manufacturer until the job was well under- way, the contractor’s workmanship was poor, and there was little input from the manufacturer. The warm weather that lowered the viscosity of the resin combined with improper seeding methods resulted in a glassy, resin-rich surface that varied in thickness by as much as 6 mm (0.25 in.) across a 75-mm (3-in.) core. Water had infiltrated some of the resin drums. After 3 years, 180 m2 (1936 ft2) of surface had debonded, beginning in the first winter. Of the 180 m2 that were repaired, 40 m2 (430 ft2) have since failed along with 60 m2 of additional TPO. Texas Two short overlay test sections in Texas failed within a short time of installation because the high-molecular-weight methacrylate primer was allowed to pond near the edge of a sloping deck and form a thick film. The thick film had a very high coefficient of thermal expansion, and it delami- nated over a large area, requiring replacement with an epoxy overlay (22). Panama, Canal Zone The Bridge of the Americas was overlaid with epoxy slurry TPO. High-molecular-weight methacrylate was used to seal the cracks on the bridge before installing the TPO. After 1 or 2 years, a considerable portion of the overlay had delaminated based on visual observations. Laboratory tests sought to duplicate the application. The initial tensile bond tests gave good strengths, but when they were per- formed after several months on the same specimens, the specimens that had been primed with the high-molecular- weight methacrylate had low bond strengths. Anecdotal experiences of others confirmed that some epoxies tend to lose bond with time when placed over a high-molecular- weight methacrylate. STRESSES IN OVERLAYS Analytical Method for Calculating Thermal Stresses Choi et al. (40) present a method for calculating interfa- cial stresses and axial stresses in TPO overlays because of changes in temperature. The method assumes (1) that there are linearly elastic stresses in overlay and substrate, (2) that the effect of the very thin adhesive layer is negli- gible, and (3) that the composite beam (overlay and sub- strate concrete) is subjected to a uniform temperature change and the difference in the thermal coefficients for the overlay and concrete remain constant during the tem- perature change. The governing differential equations and solution are presented. The three types of stresses that can be determined from this analysis are the interfacial shear and normal stress and the axial stress in the overlay shown in Figure 10. The shear and normal stresses are maximized near the end or boundary, which can be the edge of the overlay, a crack or a joint, which explains why delamina- tion always starts near one of these boundaries as shown in Figure 11. The axial stress in the overlay starts at zero stress at the boundary and within a short distance from the boundary reaches its maximum stress. The stresses are shown to be a function of the ratio of the coefficient of thermal expansion of overlay to concrete, the temperature change, the ratio of overlay thickness to sub- strate thickness, and the ratio of modulus of elasticity of the overlay to the substrate. As each of these increases, the shear, normal, and axial stresses increase. Thus, overlays that are thinner and less stiff will produce smaller stresses with the same temperature change. Graphs are provided to simplify the determination of stresses, and examples are given to illustrate the method in Figures 12, 13, and 14. The graphs are developed for differential strain because of temperature change, ΔεT = 500 × 10-6 in./in., and a given substrate modu- lus, Es = 4 × 106 psi. In the graphs, to is the overlay thickness, ts is the substrate thickness, and Eo is the overlay modulus. ΔεT is the difference in the coefficients of thermal expan- sion for the two materials, overlay and substrate, times the change in temperature. The analytical values are compared with experimentally determined stresses. Examples are shown in Appendix B. Letsch (41) shows measured stresses resulting from dif- ferential strains in the substrate and the overlay and indicates that curing, shrinkage, and thermal changes can result in stresses in the overlay and substrate. Strains were measured with a cracking frame.

21 tection TPO used to overlay a bridge in Virginia. Two resin systems were used on separate lanes: (1) modified vinyl ester and (2) polyester. Each was used with an aggregate consist- ing of 50% calcined coke breeze (an electrically conductive aggregate) and 50% silica sand. The surface was shot blasted, the primary anode system was installed, and the polymer con- crete was placed and screeded to a 12-mm (0.5-in.) thickness. SPECIAL APPLICATIONS Cathodic Protection Cathodic protection overlays have been developed and used for bridges subject to or experiencing corrosion activity in the reinforcing steel. Fontana et al. (12) describe a cathodic pro- FIGURE 10 Stresses in overlays. FIGURE 11 Shear and normal stresses near boundary (for normal stresses + = tension).

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.) FIGURE 13 Normal stresses in overlays for various thickness and modulus ratios. (For assumed values of ΔεT = 500 μ-in./in., Es = 4 × 106 psi.)

23 About 25% of the first system had to be replaced because of delamination. A current of 1 mA/ft2 was applied. It has been shown that cathodic protection overlays can be sprayed on horizontal and vertical surfaces (12). A PC made of vinyl ester and about 60% by weight of calcined coke breeze can provide a non-sag material for overhead. Wet Surfaces Ahn and Fowler (42) found that the addition of zinc diacry- late, in the range of 5% to 15% by weight of MMA, resulted in an increase in tensile bond to wet concrete by up to 50% compared with no zinc diacrylate. The addition of the same amount to polyester-styrene also produced a very good increase in tensile bond, including smooth, wet surfaces. Calcium diacrylate worked much better with epoxies, giving up to 20% increase in strength. Although this has not been used in TPOs, it is a viable solution. Deicing Overlays Virginia Department of Transportation (VDOT) conducted an evaluation of a patented deicing overlay system designed to prevent frost formation and the bonding of ice and snow to the deck surface (43). The 9-mm-thick (3/8-in.-thick) overlay consists of epoxy binder and limestone aggregate that the manufacturer states acts like a rigid sponge that stores salt-brine deicing solution, which is released when needed. Silica or basalt aggregates that are typically used to construct TPOs do not have the required absorption. Four overlays were placed on bridge decks on I-81 in Sep- tember 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) using a spray bar. Four overlays were placed on Smart Road in September 2006: two two-layer deic- ing overlays and two two-layer epoxy overlays. The two deicing overlays were pretreated with salt brine at a rate of 70.5 L per lane-kilometer (30 gal per lane-mile). One of the epoxy overlays was pretreated at the same rate and the other was untreated (43). I-81 Overlays The aggregates used in the deicing overlays had significantly higher absorption (1.70%) compared with the quartz (0.72%) and basalt (0.45%) aggregates used in the epoxy overlays. The soundness loss for the deicing aggregates was much higher (6.0% to 21.6%) compared with the loss for the epoxy overlays (1.1% to 1.9%). It can be noted that the report indi- cated that the deicing overlay aggregates reported in this study are no longer being used. FIGURE 14 Axial stresses in overlays for various thickness and modulus ratios. (For assumed values of ΔεT = 500 μ-in./in., Es = 4 × 106 psi.)

24 Bond strength tests were performed in February 2006. The thicknesses for the deicing overlays were 12 mm (0.49 in.) and 11 mm (0.46 in.), whereas the epoxy overlays were 2.5 mm (0.10 in.). The bond strengths were 1.41 and 1.50 MPa (205 and 218 psi) for the deicing overlays and 1.59 and 1.89 MPa (230 and 274 psi) for the epoxy overlays. The per- meabilities to chloride ion when tested in February 2006 were 23 and 246 coulombs for the deicing overlays and 1,226 and 1,367 for the epoxy overlays. The bare tire skid numbers for travel lanes on the bare concrete were 27 and 28 in June 2004 before the deicing overlays were installed; in October 2005, after overlay installation, the skid numbers were 59 and 60. In December 2005, the numbers dropped to 46 and 53 for the deicing over- lays. For the epoxy overlays, the skid numbers were 22 and 26 before overlay installation in June 2004. In the October after installation, the numbers were 57 and 49. No values were reported for December. Inconclusive results were obtained for ice and melting snow performance on I-81 because insufficient ice and snow events had occurred at the time of the evaluation (43). Smart Road Overlays Permeability and bond tests were not reported for the Smart Road overlays. Skid tests were performed in November and December 2006 and January 2007. All skid numbers were 57 or higher. Snow was applied artificially to the Smart Road overlays. Friction tests were performed on the pavements: 4 passes on dry surfaces, 8 with snow, 4 after the first plow, and 12 after the second plow. 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 fric- tion of bare, tined concrete pavements or bridge decks in the early stages of a snow storm before the snow removal equipment can arrive. However, no consistent conclusions could be drawn after the initial plowing for the snow and traffic conditions occurring during the tests. The difficulties encountered in obtaining a uniform coverage with “natural” quality snow and accurately defining the location of the fric- tion measurements precluded more accurate comparisons of performance of the two overlay systems (43). SERVICE LIFE Sprinkel (4) states that projections suggest that, with the exception of the methacrylate slurry and the multiple-layer polyester overlays, TPOs constructed in accordance with AASHTO specifications (6) should have a service life of 25 years. Carter (8) states that TPOs properly applied can pro- vide service lives of up to 20 years, but that maintenance will be required if the surface is intended to remain free of defects. WARRANTIES Alberta In the Province of Alberta, each TPO contract requires a 5-year warranty signed by both the contractor and material supplier (8). Bankruptcy of either party leaves the other party wholly responsible. The warranty covers failure of the wearing surface exposed to normal traffic; it does not cover failures of the substrate. Repairs of distress that occur after the work was approved by the province are required to be made at the end of the 5-year period, except that large failures, defined as more than over 5% of the deck, must be repaired within 60 “good weather days” of notification, regardless of when the accu- mulated 5% distress developed. Carter (8) notes that this has happened only twice. Even with the warranty, the contractor’s work is subject to approval by the province, and the contractor is compensated only for work that has been approved. LaGuardia Airport, New York The warranty used in the construction of LaGuardia Airport is shown in Appendix C. The warranty was executed jointly by the material supplier and the contractor. The warranty required that the contractor repair any defects that occurred within 5 years of installation. RELATIVE COST Sprinkel (4) reports that the cost of epoxy overlays, based on 1994 and 1995 bid tabulations in Virginia, was 25% of the hydraulic cement concrete overlays based on total initial cost, and 36% if based on life-cycle cost assuming a 15-year life for the epoxy TPO and 30-year life for the hydraulic cement concrete. However, the life-cycle cost for the epoxy is even lower if a 25-year life is assumed. Kansas DOT reported that the cost of milling and placement for TPOs between 2001 and 2008 was about 20% less than for silica fume overlays. Traffic control costs are much lower for TPOs because of the much shorter cure time (5 days versus 2 days) and the elimination of overnight lane closures. For a four-lane structure, traffic control for a TPO would be approxi- mately 12% of that required for a silica fume overlay (44). SPECIFICATIONS National organizations have prepared three specifications for the installation of TPOs:

25 3. Specification for Type ES (Epoxy Slurry) Polymer Overlay for Bridge and Parking Garage Decks, An ACI Standard, Reported by ACI Committee 548, ACI 548.9-08, American Concrete Institute, Farmington, Hills, Mich., 2008 (45). 1. Guide Specifications for Polymer Concrete Bridge Deck Overlays, AASHTO-AGC-ARTBA Task Force 34, Washington, D.C., 1995 (6). 2. Specification for Type EM (Epoxy Multi-Layer) Poly- mer Overlay for Bridge and Parking Garage Decks, An ACI Standard, Reported by ACI Committee 548, ACI 548.8-07, American Concrete Institute, Farm- ington Hills, Mich., 2007 (2).

Next: CHAPTER THREE Performance of Overlays from Surveys and Interviews »
Long-Term Performance of Polymer Concrete for Bridge Decks Get This Book
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TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 423: Long-Term Performance of Polymer Concrete for Bridge Decks addresses a number of topics related to thin polymer overlays (TPOs).

Those topics include previous research, specifications, and procedures on TPOs; performance of TPOs based on field applications; the primary factors that influence TPO performance; current construction guidelines for TPOs related to surface preparation, mixing and placement, consolidation, finishing, and curing; repair procedures; factors that influence the performance of overlays, including life-cycle cost, benefits and costs, bridge deck condition, service life extension, and performance; and successes and failures of TPOs, including reasons for both.

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