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11 Polymer Concrete Water Absorption Specimens made from the furnished resin and aggregate White and Montani (9) recommend that the water absorption need to be made and tested in accordance with the tests in PC be limited to a maximum of 1% by weight when tested shown in AASHTO Guide Specifications (6 ). The test in accordance with ASTM D570 (23). results should meet the minimum requirements in the table for the type of polymer used. Abrasion Gel Time White and Montani (9) recommend that overlays be tested at 125°F in accordance with ASTM D4060 (1,000 g load at The gel time needs to be monitored to ensure that the require- 1,000 cycles) (24) and maintain a wear index of less than 2.0. ments of AASHTO Guide Specifications (6 ) are met. Chloride Ion Penetration Application Rates White and Montani (9) recommend that when tested in The application rates need to be monitored to ensure that they accordance with AASHTO T277-07 (25) the "polymer and are in conformance with AASHTO Guide Specifications (6 ). system in place shall be required to register zero coulombs in the test to ensure chloride resistance." The AASHTO Guide Curing Specifications require that the permeability be a maximum of 100 coulombs at 28 days (6 ). The minimum curing time before opening to traffic is given in AASHTO Guide Specifications (6 ); however, a compres- Evaluation of Bridge Decks sive strength of 6.9 MPa (1,000 psi) based on field-cured cubes (ASTM C579, Method B) (20 ) might be obtained Carter (8) reports on the procedures used to evaluate many before opening to traffic (6 ). 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. TEST METHODS (specimens were pressurized from the bottom surface using the American Petroleum Institute Recommended Practices Shrinkage 40 test method); (3) bond strength tests using 75-mm (3-in.) cores taken randomly; (4) ultraviolet exposure tests using Many monomers and resins shrink during curing, particu- ASTM D638 (10 ) for measuring tensile strength and elonga- larly polyester-styrene and acrylics. Zalatimo (21) and Zala- tion (samples were lightly sprayed with water each day); and timo and Fowler (22) developed a test method for measuring (5) skid resistance tests done by a mobile skid trailer travel- shrinkage, including the effect of relaxation. A 150-mm × ing at 64.4 km/h (40 mi/h). 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 THIN POLYMER OVERLAY FIELD SECTIONS surface. A measuring device with a 250-mm (10-in.) gauge length is placed into the fresh PC; at different times after Many authors have reported results of TPO test sections, the PC has initially cured, one end of the unbonded sec- and some of the more significant tests are discussed in this tion is cut. Residual shrinkage stresses in the PC will cause section. In most cases, the information on the resins used the unbonded section to contract from the cut end. It has did not include tensile elongation or modulus of elasticity; been shown that when the time of cutting is increased, the rather, the generic resin type was given, for example, epoxy, measured shrinkage is reduced. For most materials tested, polyester-styrene, or methacrylate. including epoxies, polyester-urethane, and polyester-sty- rene, the shrinkage is generally nonexistent after 72 h, which Ohio Bridge Deck, 1983 indicates that relaxation has occurred. Dimmick (18) reports that a bridge deck in Ohio, constructed Tensile Elongation in 1962, had experienced transverse cracking and extensive wear. An epoxy TPO was selected primarily for the purpose White and Montani (9) recommend that cured resins have a of surface friction. The surface was shot blasted; because the minimum of 20% elongation at 40°F and 30% when tested at pH exceeded 13, the surface was acid etched to reduce the pH 73°F in accordance with ASTM D638. The AASHTO Guide to 9.2, although normally acid etching is not recommended Specifications have the requirement of 30% to 80% tensile for surface preparation. Cracks were not repaired. The sur- elongation for epoxy and polyesters (6 ). face was primed with neat epoxy. Polymer concrete consist-
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12 ing of silica sand and 10.5 (wt %) epoxy resin was batched In 1971, 16 test sections using different resins and aggre- in mixers and placed to a depth of 6 mm (0.25 in.). The sur- gates were installed. Epoxy asphalt and a combination face was finished with a wood screed to provide transverse of hard metagraywacke and soft, lightweight, synthetic irregular ridges. The area overlaid was 1,642 m2 (17,676 ft2). aggregate were selected for the overlay. In 1976 and 1977, After 10 years and 121 million vehicles, the surface was said the upper and lower decks were resurfaced with 256 m 2 to still have excellent anti-skid properties. About 2 m 2 (22 (2,760 ft2) of 19-mm-thick (0.75-in.-thick) epoxy asphalt ft2) of overlay had to be replaced because of delamination; using conventional asphalt paving machines followed by it was not known whether the delamination occurred in the compaction with rubber tired and steel drum rollers. In substrate or at the bond line. 1996, an inspection showed five types of distress: (1) small mechanical gouging depressions, (2) three locations of fire Post-Tensioned Parking Garage pitting owing to vehicular fires, (3) pot holes resulting from delamination of the lightweight concrete substrate or weak Post-tensioned slabs in a 6-year-old parking garage in Ten- bond to the epoxy coal tar chip seal (approximately 93 m 2 nessee had experienced severe freezing and thawing as a or 1,000 ft2), (4) joint crumbling that required six joints to result of an improper air void system (27 ). Tests on cores be repaired, and (5) reduced skid resistance that had not indicated concrete compressive strength of about 6,000 psi. been predicted by lab tests. Bond pull-off tests using ACI Some deformed bars and post-tensioning tendons were cor- 503R-93 (13) with 50-mm (2-in.) diameter cores gave ten- roded and exposed. The chloride ion content at a 12-mm sile bond strengths ranging from 0.84 to 2.45 MPa (122 to (0.5-in.) depth was three times the corrosion threshold level 356 psi). The performance was deemed a success for the of 0.77 kg/m3 (1.3 lb/yd3). Methyl methacrylate (MMA) PC 20-year life for a bridge experiencing 250,000 vehicles per was selected because of (1) the ability to place it in very thin day in both directions. 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 Gaul (11) gives a 25-year history of the use of epoxy allowed the garage to remain open during repairs. The dete- asphalt, including properties, manufacture, methods of use, riorated concrete was chipped out and the corroded bars and and list of applications. tendons were exposed. The surface was sandblasted and then primed with MMA primer. Deep spalls were filled with Alberta Overlays MMA PC that used pea gravel. All of the negative moment regions received a 6-mm-thick (0.25-in.-thick) MMA PC Initial Investigation overlay. Inspections were made at 1.5, 7, 10, and 13 years after repair. During the first inspection, very shallow 0.3- In an initial investigation, Carter (8) states that Alberta had mm (0.012-in.) deep crazing cracks were observed in areas waterproofed 66 bridges with TPOs. Many of the TPOs were exposed to sunlight and were attributed to the trowel finish- placed on dense concrete overlays that were heavily cracked ing that brought excess monomer to the surface, resulting owing to long-term drying shrinkage. The cracks appeared in additional shrinkage. No spalling, cracking, or delami- to propagate each year when subjected to vehicle loads in cold nation was observed until the last inspection; at that time, weather. Half-cell (copper sulfate electrode) and chloride some delamination associated with cracking in the surface content testing were performed on many of the decks, and was observed. Cracks over deformed bars and tendons were it was concluded that corrosion was continuing to develop associated with continued corrosion of the bars and tendons. and would likely reduce the service life and require a second Apparently, all of the contaminated concrete around bars major rehabilitation. An investigation of thin epoxy wearing and tendons had not been removed and corrosion had con- surfaces installed by agency crews in the 1960s showed that tinued at a slow rate. In areas where freezing and thawing some had performed well. Carter notes that on one bridge on had occurred and corrosion had not continued, the overlay which a coal tar epoxy overlay had been installed, 70% of the performed well. overlay was still intact and many of the failed areas appeared to have been caused by thermal incompatibility owing to an Epoxy Asphalt TPOs excessive thickness of epoxy having been applied. The San FranciscoOakland Bay Bridge was constructed Test Bridge in 1936, and ceramic tile embedded in mortar was used as permanent lane striping (11). In 1963 and 1964, the upper In 1984, a test bridge was selected and divided into eight and lower decks were resurfaced to cover the ceramic tile equal sections of 139.4 m2 (500 ft2) to test some of the avail- striping with a PC made of coal tar epoxy binder and quartz able membrane wearing surface systems, including some beach sand. The binder was sprayed on the surface and the parking garage membrane systems. These softer, more flex- sand was broadcast onto the binder. By 1968, the sand had ible materials performed poorly on the bridge. One system begun to polish and to be picked out, reducing the skid composed of coal tar epoxy was seeded with a very hard resistance, although the binder was in excellent condition. (Mohs hardness of 9) brittle slag aggregate. The aggregate
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13 disintegrated under tire impact, leaving tiny holes in the had increased to 2.0% at an average of 9 years. The original membrane. After 6 years, most of the membrane had worn installation had a 5-year warranty, so that at an age of 5 years away. Two other sections using silica sand embedded in the contractor had repaired all of the original defects. The epoxy resins became highly polished because of the poor amount of defective surface area in 1995 included the total wear resistance of the sand. One of these systems exhibited distress that had been repaired before and after the 5-year some debonding that was attributed to the well-graded fine warranty repairs. aggregate creating a brittle epoxyaggregate composite material that performed differently than the deck when sub- Thermal Incompatibility jected to live load and thermal stresses. The most durable of the eight systems was a flexible epoxy that used a poorly One bridge that was overlaid in 1991 experienced 10% graded basalt aggregate with a relatively high aluminum debonding in 2 years and 50% in 3 years (8). The failure oxide content. It had the highest bond strength and the best involved shear failure of the dense concrete just below the electrical resistivity readings. bond line. The thickness was 15 mm, greater than normal; that also leads to increased stress owing to thermal changes. Description of TPOs The initial strength of the polymer (the type of polymer was not given) was 25 MPa (3,600 psi), which was considerably The TPOs applied after 1985 usually consisted of two lay- higher than for other "well-performing resins that had been ers plus a tie coat, resulting in an average thickness of 6 used in Alberta." The strength increased to 30 MPa (4,350 mm (0.25 in.) (8). No primer was used. Each layer consisted psi) when exposed to ultraviolet light. The tensile elongation of liquid seeded with aggregate applied with squeegees of the polymer was found to have decreased significantly and rollers to seal the deck surface. Excess aggregate was from its original 30%. It was concluded that thermal incom- removed after the resin hardened. The tie coat consisted of patibility with the substrate caused the failure because of a thin layer of resin used to seal pinholes and voids in the loss of flexibility. composite layer. Aggregate In 1988, six bridges with low traffic volume were repaired with a less expensive system that had only one seeded layer A bridge placed in 1990 used red basaltic aggregate on applied on a nonseeded primer. Permeability tests indicated one side of the bridge and green trap rock on the other side better waterproofing than the system with two seeded layers (8). After 2 years, it was observed that more red aggregate and no primer (8). was accumulating in the gutter lines of the deck than green aggregate. Further testing using cores indicated that five In 1989, the two-layer system was changed by applying times as many empty sockets were left by red aggregate. The the tie coat first as a primer, followed by the two seeded lay- problem was attributed to the fact that the red aggregate was ers. Three bridges were repaired by using a premixed PC more rounded and had a lower fracture-face count. In addi- that was screeded; the main advantage is the speed at which tion, after 5 years of service, the amount of lost or debonded they can be placed on large bridges, resulting in labor sav- overlay was twice as much on the red side even though the ings and reduced closure time. A possible disadvantage is overlays were placed at the same time by the same contrac- the possibility of entrapped air at the bond line, which would tor. A study of other bridges that used the red, green, and a reduce bond strength (8). less frequently used black aggregate was conducted. It was found that under similar conditions of age and traffic, the Performance of 21 Bridges red overlays were debonding 25 times more rapidly than the black overlays and 19 times more rapidly than the green ones. Carter (8) reports on 21 TPOs of a total of more than 100 that Stressstrain tests on cylinders using the same polymer and had been placed in Alberta beginning in the 1960s. Typi- the three different aggregates showed that the polymer con- cally, it was found that the failure of TPOs resulted "from crete made with the red aggregate could absorb only 70% as the basic incompatibility of polymer concrete and portland much energy (area under the stressstrain curve) than the cement concrete, manifested as debonding or shearing of other materials (8). the overlay from the concrete." Many of the bridges had been overlaid previously with dense concrete that devel- Contractor Experience oped numerous cracks. Many of the bridges, especially the ones with the largest spans, had steel superstructures that A study of 71 bridges for durability also evaluated the per- were more flexible and developed more cracking and also formance of contractors (8). The overlays constructed by the received more deicing salt than the average deck. In 1990, most experienced TPO contractors (i.e., those who had done the accumulated damage to the TPOs was 0.6% of the total the most work) were significantly more durable than those 22,052 m 2 (237,000 ft2) installed on the 21 bridge decks constructed by contractors with lesser amounts of installa- between 1985 and 1987. By 1995, the failed surface area tion experience.
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14 Ability of TPOs to Protect Nondurable Concrete tic chip coats over aging TPOs to renew their skid resistance and to extend the life of the overlay (8). Carter reported that TPOs were applied to several bridges with concrete decks 56 bridges have been treated using inexpensive chip coats; of substandard quality and durability based on Carter's the results were satisfactory. experience (8 ). One bridge deck had little entrained air, and the surface was badly scaled on one side after one winter Virginia Multiple-Layer Overlays of service. Another bridge had a wavy surface owing to hand screeding, and the cover over the steel varied "sub- Virginia has used many TPOs over the years, and Sprinkel stantially." The bridge carried heavy traffic, received heavy (16 ) reported on 18 multiple-layer overlays and one single- applications of deicing salt, and had many freezing and layer overlay placed between 1981 and 1987. The binders for thawing cycles. A third bridge had a 1972 overlay that had the multiple-layer overlays included four polyester-styrenes, been placed with the expectation of providing 10 to 15 years one polyester amide alkyd, one MMA, three EP5-LV epox- of life. By 1986, the overlay was partially debonded and ies, and two flexible epoxies. A single-layer high-molecular- had moderate salt scaling. A single-layer TPO was placed weight methacrylate overlay was installed. After all major with the goal of providing 10 years of service life. It was spalls were repaired, the bridge decks were shot blasted, concluded that "the extension of deck service life result- except cleaning with compressed air was used in the high- ing from the thin overlays at these inferior concrete sites molecular-weight methacrylate single-layer overlay. The ini- appears to be from 5 to 12 years. Since the cost of deck or tiated and promoted resins were sprayed or broomed onto entire bridge placement is so much higher than the overlay the clean surface, and before the resin gelled, aggregate was cost, these polymer systems were successful in reducing broadcast onto the surface. After curing, the excess sand was life cycle costs." It was noted that the deck life was sig- broomed or vacuumed off the surface. The additional layer nificantly reduced when a significant amount of reflective or layers were applied in a similar manner. Three or four lay- cracking was present in the concrete. "Apparently, since the ers were applied for the polyesters; the epoxy overlays used polymer overlays did not effectively seal the wide, moving only two layers. The high-molecular-weight methacrylate cracks, deck deterioration proceeded below the overlay in overlay had only one layer. The aggregate was clean, dry, the cracked areas." angular silica sand. Effectiveness in Sealing Deck Cracks Tensile Bond Strength Carter (8) notes that it is difficult to know which cracks are Virginia requires a tensile bond strength test, based on ACI reflective cracks prior to installation of TPOs, and that it 503R (13) or ASTM C1583 (14), to ensure that the instal- may be better to install the overlay and then repair the cracks lation procedure would give the target strength of 1.7 MPa later. In his opinion, even when crack repairs are made, they (250 psi) or more. The contractor was required to install two may last only 5 to 10 years, but the life of the overlay is layers of an overlay, 0.3 m by 0.9 m (1 ft by 3 ft), on each likely to be 15 to 20 years (8). One bridge had about 1,500 span or 167 m2 (200 yd2), whichever was the smaller area. m (5,000 ft) of cracks in 1985 before installing the overlay. Their experience indicated that a typical standard deviation About 185 m (600 ft) of "apparently actively moving cracks" was 0.27 MPa (40 psi), and average bond strength of 1.52 were repaired by routing and using an epoxy caulking mate- MPa (220 psi) was required for satisfactory performance. rial. After 5 years, approximately 46 m (150 ft) of cracks had The tensile bond strengths were found to decrease with reflected through the overlay; after 10 years, it had increased time. Initially, failures were in the concrete substrate, but to 215 m (700 ft). It was thought that ultraviolet radiation had with time the failures were in adhesion or near the bond line. caused the polymer to lose flexibility over time. In bridges on which traffic was allowed on the shot-blasted surface before overlay application, the initial bond strengths Thickness of TPOs in Cold Climates were low (16 ). Carter (8) notes that TPOs are more durable in Alberta when Shear Bond Strength they are thin. The reduction in temperature [to as low as 40°C (40°F)] causes the polymer to become more brittle Guillotine shear strength tests were performed on cores at the same time that interfacial stresses are developing. The taken from the bridge decks (16 ). Some cores were thermally stress is proportional to the thickness of the polymer. Exces- cycled from -18°C to 38°C (0° to 100°F) three times each sive thickness can lead to bond failures. day. For some overlays, the thermal cycling gave good cor- relation with tensile bond strength test results from the field. Repair of TPOs It was concluded that environment had a greater effect on the bond strength for polyesters than for the epoxies, and that Because the service life of TPOs is affected by ultraviolet degradation of bond strength with time leads to delamina- radiation and traffic wear, Alberta began placing thin asphal- tion for some overlays within 10 years.
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15 Rapid Chloride Permeability tiple layer, slurry, and premixed overlays is given; proper- ties of epoxy, polyester, and methacrylate binders and PC All polyester and epoxy overlays displayed very low (100 to are presented with the appropriate test method for each prop- 1,000 coulombs) or negligible (<100 coulombs) permeabil- erty; and typical polymer concrete application rates for the ity initially; the high-molecular-weight methacrylate overlay three types of application methods are given. displayed low permeability (1,000 to 2,000 coulombs). After 1 year, the brittle polyester had a moderate permeability The 14 bridges were evaluated in 1991 and 1995. Three (2,000 to 4,000 coulombs). After 4 years, the stiffer epoxy overlays, each constructed with multiple-layer epoxy, multi- had the lowest permeability, and after 5 years, the flexible ple-layer epoxy urethane, premixed polyester, and methac- had the lowest, both being in the very low category. After rylate slurry, and two overlays installed with multiple-layer 100 thermal cycles in the laboratory, only the brittle polyes- polyester, were included in the evaluation. The overlays ter and the epoxies had a negligible permeability; the MMA, ranged in age from 6 to 19 years. high molecular weight, and some of the other polyesters had low or moderate values (16 ) Tensile Bond Strength Electrical Resistivity The tensile bond test was a modified version of Virginia Test Method 92. This method is similar to ACI 503R (13) but dif- Electrical resistivity tests (28 ) were performed to deter- fers by providing a swivel attachment to the cap and the top mine the presence and extent of microcracks. Only the flex- hook of the test device to minimize eccentricity. The results ible polyester had no significant cracks until 3 years after indicated little change in initial tensile bond strengths of placement; all others had extensive cracking after 1 year or more than 1.65 MPa (240 psi) for the multiple-layer epoxy, less. However, the permeability tests indicated that the other multiple-layer epoxy urethane, and the premixed polyester overlays were "providing significant protection against chlo- over the life of the overlays; the multiple-layer polyester ride penetration" (16 ). overlays had lost considerable bond strength [from over 2.0 MPa (300 psi) to about 0.50 MPa (75 psi)] and were projected Half-Cell Potential to fail within 10 years. There were insufficient data to evalu- ate the MMA slurry overlays (15). Copper sulfate half-cell potential readings (26 ) indicated that only four small areas on four spans had a 90% corrosion Permeability probability. Over a 6-year period, the half-cell readings did not change significantly (16 ). Permeability performance based on AASHTO T277-07 (25) tests in 1995 and from a previous project was given. The Skid Resistance results indicated that the lowest permeability (<100 cou- lombs) was provided by the methacrylate slurry, and that All overlays had adequate skid resistance at the time the negligible to very low permeability (<1,000 coulombs) was overlays were installed, and the values are reported in associated with the multiple-layer epoxy and epoxy ure- Sprinkle (16 ). The overlays made with the more rigid epoxy thane and the premixed polyester. Multiple-layer polyester showed a significant reduction in skid resistance after 1 year had greater increases in permeability but was predicted to of service; the reduction was because these overlays used provide good protection for 10 years (15). less resin and finer sand than the other overlays in the pro- gram. Virginia no longer uses this epoxy (16 ). Skid Resistance Wear Based on ASTM E524 (29) (smooth tire), acceptable skid numbers (<33 coulombs) were being maintained for all over- The most wear occurred in the travel lanes. The greatest lays except MMA slurries, which were showing a downward wear occurred for the brittle polyester-styrene (2.5 mm or trend (15). 0.10 in. in 5 years), but that rate is 23% of the wear reported for latex-modified concrete. The conclusion was that the Durability overlays would likely delaminate or exhibit an unacceptable skid resistance before the overlays wear through (16 ). Polymer concrete was tested for freezing and thawing in accordance with ASTM C666, Procedure A (30 ); modifi- Nineteen-Year Performance cation by the addition of 2% sodium chloride to the water had shown a durability factor of over 90% after 300 cycles, Sprinkel (15) provides a summary of performance of TPOs considerably greater than the minimum factor of 60% on bridge decks in California, Michigan, Ohio, Virginia, and generally accepted for concrete. Polymer concrete had Washington. A summary of aggregate gradations for mul- good resistance to wear. Projections based on tensile bond
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16 strengths, permeability, and skid resistance, for the over- (8,000 psi) and a tensile elongation of 5%. The surface was lays, with the exception of the MMA slurry and multiple- shot blasted and primed with either high-molecular-weight layer polyester overlays, indicated a service life of at least methacrylate or an unsaturated diaromatic glycol fumer- 20 years (15). ate. The aggregate was 12 mm (0.5 in.), with less than 25% crushed particles. The overlay was installed using a contin- Epoxy TPO Overlays uous screw-type mixer and a paving machine. Dry screen- ings were broadcast on the surface to provide improved The advantages of epoxy TPOs were given, including excel- skid resistance. The overlay was 3.6 mi in length and had a lent bond strength, unaffected by alkalinity of concrete, little 19-mm (0.75-in.) thickness. Krauss (33) states that, "Over shrinkage, low modulus, high strength-to-weight ratio, and 25 bridge decks have been overlaid with polyester-styrene not flammable. Epoxy PC consists of resin, hardener, and concrete overlays and all the overlays are performing aggregates. Nabar and Mendis (31) provide a list of key proj- well." He states that in 1988 there had been no delamina- ects using flexible epoxy binder that had been in service for tion on any polyester-styrene concrete overlay placed by 10 years. The authors provide a good summary of surface contract. No overlay since 1983 had shown signs of wear preparation, overlay application including multiple-layer or cracking. method or slurry method, and curing quality assurance pro- cedures, service life, trouble-shooting procedures, and loss Several Epoxy TPOs of skid resistance. Two epoxy overlay test sections were reported by Dimmick Evaluation results of four bridges in Michigan, Ohio, Vir- (34). ginia, and Washington are given. Toll Booth Lanes Fort Worth, Texas, Overlays Portland cement and epoxy polymer concrete were tested Zalatimo and Fowler (22) report on different resins used to side by side at toll booth lanes into Newark Airport in 1977. construct small overlay test sections on two bridges in Fort The portland cement had about 40 MPa (6,000) psi compres- Worth, Texas. One bridge used (1) high-molecular-weight sive strength. The epoxy concrete had 14% epoxy by weight. methacrylate, (2) four hybrid polyester-urethanes (three low The surface was primed and the hand-mixed epoxy concrete modulus and one high modulus), (3) experimental epoxy was placed on portland cement concrete slabs to a depth of with a high modulus, and (4) two commercially available 0.16 mm (0.625 in.) in the wheel paths. After 6 years, the epoxies. The PC was batch mixed and placed in a 12-mm portland cement concrete was badly worn to a depth of 13 to (0.5-in.) thickness with a vibrating screed. Additional aggre- 19 mm (0.5 to 0.75 in.) and had about 1 m 2 (10 ft2) of deeper gate was broadcast on the surface to obtain improved skid spalling. The portland cement concrete wore out after about resistance. The second bridge used two polyester-urethanes, 97 million vehicle passes. The epoxy polymer concrete had experimental polyester, and an experimental epoxy, which no surface defects and still had an excellent textured surface. were applied as multiple-layer overlays over a high-molec- After 15 years, the epoxy polymer concrete was still pro- ular-weight methacrylate primer. Two layers were applied, viding excellent skid resistance and had shown about 3-mm resulting in a thickness of about 9 mm (0.375 in.). The over- (0.12-in.) wear after 243 million vehicular passes. One small lays generally performed well, except that two of the hybrid patch had to made, and a small gouge had occurred in the resin overlays failed owing to the primer being allowed to surface about 12 mm (0.5 in.) deep. pond and form a thick layer. Because of thermal stresses, it failed within the first couple of months. The 5-year evalua- Bridge Deck Overlays for Skid Resistance tion found that most were in good condition, although some had polished on the surface owing to inadequate aggregate In 1983, the Ohio DOT found it necessary to overlay three seeding for texture. bridges to obtain improved skid resistance during times of rain, snow, and ice. The substrate had transverse structural California I-80 cracks, which exhibited spalling and grooves that were com- pletely worn down in many places. The surface was shot Maass (32) reports that the Donner Pass section of I-80 in blasted, the epoxy polymer concrete was mixed in drum California that was overlaid in 1986 has performed well. In mixers, and it was placed on a surface primed with neat 1983, the section of highway carried an average daily traf- epoxy to an average depth of 6 mm (0.25 in.). It was finished fic of 9,750 vehicles, of which 950 were trucks. The average with a wood screed to provide good texture. The total area annual rainfall is 1.54 m (61 in.) and the average snowfall of overlay placed was 1,637 m2 (17,676 ft2). After 10 years, is 10.4 m (410 in.). Two resins were used--one with a ten- 120.8 million vehicles had passed over the overlay. It still had sile strength of 17 MPa (2,500 psi) and a tensile elongation excellent skid resistance. Only 0.09 m2 (1 ft2) has had to be of 35%, and another that had a tensile strength of 55 MPa replaced; the cause of failure was unknown.
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17 Washington Overlays In 2007, the Materials Bureau evaluated 15 of the TPOs. Among the findings were Three epoxy and two MMA TPOs were installed and moni- tored. For all overlays, the decks were shot blasted prior to · The MMA overlay was the only one of the 15 to have placing the overlays. The epoxy overlays were placed using an failed. It had several spalls with about 90% of the over- epoxy primer, then a coat of epoxy followed by an application lay remaining and 80% to 90% of the friction aggre- of aggregate. After curing, the excess aggregate was removed gates intact. and an epoxy seal coat was applied. The MMA overlays used · The polyester overlay was in very good condition, with an MMA primer and a slurry application of MMA and aggre- some polishing observed. gate with the thickness controlled using gauge rakes. Addi- · The urethane overlay was in excellent condition. tional aggregate was broadcast on the surface. The results of · The 12 epoxy overlays were found to be performing the 10-year monitoring were reported in 1995 (35). acceptably although several distresses were noted: Short crack in one; Tensile Bond Strength One appeared to have been poorly installed and exhibited small spalls; 90% of the overlay was intact The average initial tensile bond strength was 2 MPa (297 psi) and 80% to 90% of the friction aggregate remained; for the epoxies, which was greater than the 1.72 MPa (250 Two were very thin owing to wear or installation, psi) specified. The average for the MMA was only 1.45 MPa with 75% to 95% of the overlay remaining; (211 psi). After 1 to 5 years of age for the overlays, follow-up One had small delaminations, with 90 to 95% of the testing was performed. For the epoxies, the average strength overlay remaining; and had reduced slightly to 1.89 MPa (274 psi), but for the MMA The other seven were in very good to excellent con- the strength had reduced to 0.98 MPa (143 psi). dition, with 90% or more of the overlay remaining. Frictional Resistance New York DOT conducts friction tests annually and uses ground-penetrating radar to determine whether TPOs For epoxies, the initial average skid number was 70 but waterproof the decks and retard the corrosion rate. It has reduced to 20 after 7 years. For the MMA, the initial aver- experimented with using one-coat overlays instead of two, age reading was 40, and it reduced only slightly to 39 after sandblasting in place of shot blasting, and using boiler slag 9 years. instead of the normally specified aggregates. Chloride Ion Alabama The average permeability to chloride ion as measured by Alabama placed four 6-mm (0.25-in.) polyurethane, twelve AASHTO T277-07 (25) was 0 for the MMA overlays and 3 9-mm (0.375-in.) polyester, two 19-mm (0.75-in.) low- coulombs for the epoxy overlays. modulus epoxy, and one 12- to 19-mm (0.5- to 0.75-in.) asphaltic-based Novachip overlays. The performance of the New York polyurethane was poor, the polyester was variable, the low- modulus epoxy was excellent after 8 years, and the Novachip In 1993, New York DOT performed a study of overlays was excellent after 3 years. that involved a survey of other states and an evaluation of its own TPOs that were 5 to 7 years old. It had placed Montana three different resin systems: polyester, MMA, and flex- ible epoxy. New York DOT concluded that the newer resin Four different overlays were installed on 13 bridges in Mon- systems "support optimism to suitability and durability." It tana; two portland cement concrete, one acrylic modified was further concluded that the overlays in the state appear concrete, and a low-modulus epoxy. On a single bridge, an to meet expectations. New York DOT recommended the use MMA overlay was installed. Both the epoxy and the MMA of TPOs for only two applications: (1) for bridges where exhibited limited cracking but no significant delamination weight was critical such as moveable spans and (2) bridges or dramatic loss of surface roughness after 2 years. The for which extended delays would be intolerable, such as in evaluation period was not long enough to make a thorough urban areas (36 ). assessment. Since 1999, New York DOT has installed 44 TPOs (37 ). Louisiana Thirty-eight were epoxy, and one each was MMA, polyurea, polyester, polyurethane, and vinyl ester. One was not identi- Four different epoxy TPOs were applied to a bridge in fied as to the resin type. The total area of bridges overlaid Louisiana in 1985 to evaluate their performance as fric- was 18,832 m2 (202,632 ft2). tion surfaces primarily and as sealers secondarily. After
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18 5 years, an evaluation showed the surface friction as mea- found to have chloride in excess of 11 lb/yd3, and the pur- sured by the British Portable Tester and ASTM E274 (38 ) pose of the overlay was to provide additional protection. skid trailer to be very good for two of the epoxies and less effective for the others. All remained bonded and resisted The popularity of the TPOs has resulted from the lower cracking (17 ). cost of the installation and traffic control because of much shorter periods of lane closures than for bonded cement Kansas overlays. Typically, for a silica fume overlay, the structure is closed overnight for 20 days and requires that temporary The Kansas Department of Transportation (KDOT) placed traffic signals be installed; in comparison, the TPO requires its first overlays in 1999. Four contractors placed approxi- flaggers for only 5 days and is open overnight (31). mately 100 linear feet (333 yd2) each on the same bridge. The four materials, all epoxies, had similar properties. The LaGuardia Airport, New York bridge deck was shot blasted using International Concrete Repair Institute (ICRI) Concrete Surface Preparation (CSP) The two runways at LaGuardia Airport in New York were Standards 5 to 7 for the desired texture. Flint rock was used constructed more than 30 years ago. Texture had been main- for the aggregate. In 2000, bond failure occurred in all four tained by cutting grooves in the concrete surface. But even- sections of overlays. The failure was determined to be caused tually, it was found to be structurally unacceptable to cut by the presence of a bond breaker (said to be a byproduct of away more of the section to reestablish the grooves. It was alcohol production) on the original concrete. Saw cuts were decided to place a TPO because of its projected service life made outside the delaminated areas, and the contaminated and the reduced time required to place the overlay and return concrete was removed by sandblasting and chipping. The the runways to service. The two runways accommodate overlays were replaced with the same materials and same more than 1,400 aircraft daily. procedures as used initially. After 9 years and approximately 21,000,000 vehicles, with 30% heavy trucks, no problems Test sections were placed using epoxy and MMA. Two have been experienced. The skid coefficient was found to be epoxy test sections were installed, one using the slurry 53 using a ribbed tire in 2003. method and the other using the broom-and-seed method. The slurry method consisted of mixing the aggregate and KDOT has placed more than 100 TPOs with the goal of resin and placing the slurry in one operation. The broom- minimizing water and chloride intrusion to preserve the and-seed method consisted of placing a layer of resin and structures. (In addition to the overlays placed by KDOT, then broadcasting aggregate having a nominal size of 1/8 four counties have placed 13 TPOs.) Some structures have in. into the resin. Four applications were placed to obtain the had minimal spalling, which was repaired. Many have had required ˝-in. overlay. Based on the test sections, the epoxy delaminated silica fume or high-density concrete overlays, resin applied by the broom-and-seed method was selected. and because the surface had not failed, the decks were shot Visual inspection showed the epoxy slurry method and the blasted before placing the TPOs. Where shallow delamina- MMA test sections did not have a uniform surface texture, tions had occurred, the loose concrete was removed, the with some areas having a glassy appearance. The broom- area repaired, the entire deck was shot blasted, and the and-seed method provided a uniform surface with excellent TPO placed. The intent of KDOT is to place the overlays frictional resistance. on decks that are not seriously deteriorated to preserve the structure. The repair work was initiated and represented the first major runways to be overlaid with an epoxy TPO. The work TPOs on three new bridge decks have been installed for was performed between 6 a.m. Saturday and 6 a.m. Monday, different construction errors. One deck had concrete that weather permitting. The surface was shot blasted to produce exhibited high permeability and low density because of minimum bond strength of 200 psi, and bond tests were per- concrete consistency problems. Another had reduced cover formed every weekend before application of resin to confirm because of a malfunction of the screed. A third had been con- that the substrate had adequate bond strength to achieve the structed with a corrosion-inhibiting admixture, and exten- specified strength. Bond tests were performed by bonding sive cracking in the deck occurred. The TPO was placed to 100-mm × 100-mm (4-in. × 4-in.) steel plates to the concrete seal the cracks. The first two bridges had TPOs applied using surface and pulling in direct tension in accordance with ACI 50% greater amounts of epoxy than the normal overlay. The 503R (13). The overlay was constructed by applying four third used a standard two-coat system. applications of epoxy resin and aggregate. One new bridge was designed for a TPO to be applied Prior to opening the runways to traffic, bond tests were before opening to traffic. The bridge is on a service road performed to determine whether the specified bond strength heavily trafficked by trucks hauling sand and salt and trucks of 1.4 MPa (200 psi) was met. The specified strength was accessing a KDOT shop. The previous bridge deck was met every weekend after 9 hours of cure time. The bond