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

Chapter: CHAPTER FOUR Proven Practices

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Suggested Citation:"CHAPTER FOUR Proven Practices." 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 FOUR Proven Practices." 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 FOUR Proven Practices." 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 FOUR Proven Practices." 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 FOUR Proven Practices." 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 FOUR Proven Practices." 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 FOUR Proven Practices." 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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32 CHAPTER FOUR PROVEN PRACTICES Based on the findings from the literature and the agency surveys, the following practices have been found to be useful. These are not intended to be specifications; rather, they summarize the important preservation methods that agencies/owners have found to produce long-lasting, durable TPOs. CANDIDATES FOR OVERLAYS Sprinkel (15) states that the bridges that are the most likely candidates “(1) are those that are in need of a skid-resistant 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, reduc- tions in overhead clearance, and modifications to joints and drains must be held to a minimum.” Harper (7) concludes, “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. Decks that have more than 5 to 10% of area that is unsound have been found to continue to experience problems after the overlay is placed.” Sprinkel (15) 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 (1) 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. (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, espe- cially 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 preventive maintenance than for rehabilitation. Resins are too expensive to be used on excessively rough or deterio- rated concrete surfaces. OVERLAY TYPES The types and recommended uses for each are as follows: Multiple-Layer Overlays Multiple-layer overlays are best used on decks that have good ride quality because the overlays follow the contours of the deck surface (15). Slurry and Premixed Decks that have many surface irregularities are the best can- didates for slurry and premixed TPOs (15). MATERIALS Binders Many polymer-based binder systems have been developed for protecting bridge decks. Epoxies (including modified epoxy urethanes), polyester-styrenes, and MMAs have been the most widely used. Earliest attempts to seal decks from ingress of water and waterborne deicing chlorides with poly- meric membranes emphasized the need for including aggre- gates to provide skid resistance in wet or freezing weather. To accommodate this need, three overlay methods evolved. The first, the multiple-layer method, emulated asphaltic seal coats, and the second, the premixed, as well as the third, slurries, emulated asphalt concrete overlays. Multiple-Layer Overlay The multiple-layer PC overlay is thinly applied and often used to seal the bridge deck while masking any unsightly repairs under a well-bonded, uniform, durable, skid-resis- tant cover. This method is often referred to as “broom-and- seed” because the method involves spreading the somewhat viscous resin system over the deck and then immediately seeding the surface with the aggregate. After the first appli- cation has set, a second broom-and-seed operation is per- formed and allowed to cure. It may be repeated again as needed or done only one time if adequate skid resistance or waterproofing can be achieved.

33 A binder system is required that has a viscosity suffi- ciently low to spread easily, and relatively thinly, over the deck, bonding well to the deck and to the aggregates that are dispersed into the surface. Additionally, the binder system must be low enough in solvents and nonpolymerizing chemi- cals to preclude pinholes or permeability. Finally, the cure system for the binder must provide adequate working time to apply the binder wherever needed and to adequately broad- cast and bond the aggregate into the binder before becoming too viscous, and then curing relatively quickly. The recom- mended binder for multiple-layer overlays is epoxy. Premixed Polymer Overlay The premixed TPO is typically specified for thicker over- lays, typically 75 mm (0.75 in.) and up, used for accommo- dating uneven or rough riding surfaces, or where the thicker, lower modulus polymer concrete can resist the stress and impact of tire chains. Epoxy and polyester-styrene are the recommended resins for premixed overlays. The requirements of the binder for the premixed TPO are not necessarily different from the binders used in the mul- tiple-layer system. However, because the premixed system incorporates the aggregates into the resin before placement on the deck, resin viscosity and rheology would permit a low percentage of resin while permitting good workability. The premixed systems usually require a primer to ensure a good durable bond between the cohesive polymer matrix and the deck. For polyester-styrene resins, the primer is typically a high-molecular-weight methacrylate that penetrates into the concrete surface and provides for excellent mechanical bond to the concrete while providing chemical bonding to the overlay matrix. Additionally, the primer prevents long-term deterioration of the polyester at the concrete interface owing to alkaline attack when wet. Premixed systems are cohesive enough to be tined or screeded to provide more skid resis- tance. Aggregates are sometimes broadcast over the screeded surface to enhance the surface friction of the overlay. Slurry Overlays Like the premixed system, the slurry incorporates aggre- gates into the binder before placement on the deck, but the lower viscosities of their binders, such as epoxies and meth- acrylate, require a well-graded fine filler component to help support and more uniformly disperse the larger sand par- ticles at the desired depth. They are normally thinner than premixes and slightly thicker than multiple-layer systems, somewhere between 6 and 12 mm (0.25 in. and 0.5 in.). They are frequently applied with a gauge rake and sprinkled with an angular aggregate. Slurries also rely on a primer of the substrate before the placement of the overlay. Slurry systems usually require a seal coat to help bind the aggregate that is seeded over the surface for additional skid resistance. Epoxies and methac- rylates are the recommended resins for slurry overlays. Cured Properties The cured binders need to possess certain properties to perform well in TPOs. These properties include high bond strength to concrete substrates and the embedded TPO aggregates, high tensile elongation, and a very low modulus of elasticity (compared with the concrete substrate) to off- set the higher coefficients of thermal expansion. They must also exhibit very low permeability to water, as well as good resistance to tire abrasion, acid rain, concrete alkalinity, and ultraviolet exposure. Commercially available binder systems for the TPOs include several types of polymers, including epoxies (modi- fied with copolymers in some cases), styrenated unsaturated polyesters, vinyl esters, and polyurethanes. Table 2 lists properties for several of the binder systems that are used on bridges (15). AGGREGATES TPOs require clean, dry, hard aggregates, including angu- lar silica sand, basalt, trap rock, or flint. Most contractors use prebagged aggregates supplied by the overlay material supplier to ensure that the aggregates will be free of dirt, dust, oils, and moisture, and will have the correct grading for the specific application. Known standard bag weights also make it easier to keep track of the aggregate application rate, although large bags can result in segregation and the possi- bility of the fines collecting in the bottom of the bags. Multiple-Layer Aggregates The aggregates typically specified for multiple-layer TPOs are hard (6 or higher for basalt and 7 or higher for other min- eralogies on Mohs scale), angular, and tough (nonbrittle), and they are typically either single-sized or a gap-graded blend of several complementary sizes. Basalts (containing at least 10% aluminum oxide), calcined bauxite, some natural granites, and angular grained silica sand are all commonly used. Their size is usually very near a no. 8 sieve to keep the overlay thin, yet skid resistant. Premixed Aggregates The aggregates for a premixed system require a few smaller sizes to uniformly distribute, embed, and support the largest aggregates that provide durable surface friction. The aggre- gates used in the premixed systems tend to be well graded and more regularly shaped, like siliceous river pea gravel and natural river sand, because they pack more easily and

34 help reduce the resin content. Topping aggregate, like the aggregates in the multiple-layer systems, however, must be angular, hard, and tough for long-term performance. Slurry Aggregates Similar to the premixed system, aggregates must be small and well graded. Additionally, a finely graded silica flour or other filler is introduced to help build the apparent viscosity or to add rheology and support the larger aggregates in the matrix. Table 3 lists common gradings for some of the aggregate systems used for TPOs. The durability and the skid resistance of TPOs are greatly affected by the relative volumes and distribution of the aggre- gates into the binder system. Also, some of the materials rely on a primer to ensure the best bond to the concrete substrate over time, and MMA slurry systems typically require a seal coat for better retention of the exposed friction aggregate course. Application rates for TPOs are listed in Table 4. QUALIFICATION OF SUBSTRATE Evaluation of Substrate The deck is to be sounded for delamination, and the areas from which concrete is to be removed need to be clearly marked. The area needs to be evaluated for corrosion activ- ity using the copper sulfate electrode method in accordance with ASTM C876 (26). It is important that the concrete in areas where the chloride content exceeds 0.77 kg/m3 (1.3 lb/ yd3) be marked for removal. The concrete substrate should have a minimum tensile rupture strength of 1.0 MPa (150 psi) based on ACI 503R (13) or ASTM C1583 (14); other- wise, the concrete must be removed and replaced. Repair Concrete needs to be removed in areas determined by the evaluation of the substrate. It is important that vertical saw be made to a minimum depth of 25 mm (1 in.) with care taken TABLE 2 POLYMERIC BINDER SYSTEMS FOR TPOs Property Epoxy Polyester Methacrylate Test Method Viscosity, Poise 7–25 1–5 11–13 ASTM D2393 Gel Time, Minutes 15–45 10–25 15–45 AASHTO T237 Tensile Strength (Binder) MPa @ 7 days 13.8–34.4 (2,000–5,000 psi) 13.8–34.4 (2,000–5,000 psi) 3.4–8.3 (500–1,200 psi) ASTM D638 Tensile Elongation (Binder) % @ 7 days 30–80 30–80 100–200 ASTM D638 PC Compressive Strength, MPa @ 3 h Min. 6.9 (1,000 psi) Min. 6.9 (1,000 psi) Min. 6.9 (1,000 psi) ASTM C579 PC Compressive Strength, MPa @ 24 h Min. 34.4 (5,000 psi) Min. 34.4 (5,000 psi) Min. 34.4 (5,000 psi) ASTM C579 PC Tensile Bond Strength, MPa @ 24 h Min. 1.7 (250 psi) Min. 1.7 (250 psi) Min. 1.7 (250 psi) ASTM 1583 PC Cure Time @ 32°C (90°F), ha 2 2 2 ASTM C109 PC Cure Time @ 24°C (75°F), ha 3 3 3 ASTM C109 PC Cure Time @ 16°C (60°F), ha 6–8 5–6 4 ASTM C109 a Time required to obtain compressive strength = 6.9 MPa (1000 psi). Source: Sprinkel (15). TABLE 3 TYPICAL AGGREGATE GRADINGS FOR TPOs (Percentage Passing Sieve) Sieve Size Multiple-Layer Overlays Slurries: Sand Slurries: Fine Fillers Premix Overlays 0.13 100 0.10 83–100 No. 4 100 62–82 No. 8 30–75 45–64 No. 16 0–5 100 27–50 No. 20 90–100 No. 30 0–1 60–80 12–35 No. 40 5–15 No. 50 0–5 6–20 No. 100 0–7 No. 140 100 No. 200 98–100 0–3 No. 270 96–100 No. 375 93–99 Source: Sprinkel (15).

35 FIGURE 15 Fiber fabric applied previous to overlay over bridge joint. Surface Preparation The deck surface must be cleaned prior to placement of the TPO to remove all contaminants, including oil, grease, dirt, asphalt, paint, carbonation, weak surface mortar, cur- ing compounds, and laitance. The surface is to be shot blasted the day of the placement, preferably just before overlay placement. A reasonable texture can be achieved by meeting the ICRI CSP 7 profile. Oil-free and moisture- free compressed air can be used to remove dust or debris just before application of the resin. The surface should be dry as determined by ASTM D4263 (46) modified to keep the plastic sheet in place a minimum of 2 hours. Some parts of the deck, including low areas and other areas that drain slowly, such as gutters, dry more slowly and need to be tested to be certain that the surface is sufficiently dry to receive the TPO. not to cut reinforcing steel. Concrete needs to be removed in such a manner as to not weaken or crack the surrounding sound concrete. Chipping hammers heavier than 15 lb are not to be used. It is important that concrete be removed beneath the steel to a depth of 12 mm (0.5 in.) or three times the diameter of the largest size aggregate, whichever is greater, in areas where the steel is corroded or the chloride content exceeds 0.77 kg/m3 (1.3 lb/yd3) at the level of the steel. Final cleaning could be by shot blasting or grit blasting; shot blast- ing cannot be used for deep patches. The steel is be cleaned from corrosion scale and other contaminants. Materials for repair are to be low shrinkage and applied in accordance with the manufacturer’s instructions. The repair material is to be compatible with the resins used in the TPO. If a hydraulic cement repair material is used, it needs to dry for a minimum of 28 days before placing the TPO unless bond tests show that earlier application is acceptable. Latex- modified concrete repair materials need to be wet cured for 2 to 3 days before beginning the drying process. Grinding might be considered to remove rough or unlevel areas. Cracks wider than 1 mm (0.04 in.) need to be filled with a gravity-fill resin that is compatible with the overlay primer or resin. It has been noted that an application of high-molec- ular-weight methacrylate for crack repair before installation of an epoxy TPO resulted in delamination of the (epoxy) overlay, and the reason was believed to be the incompat- ibility of the materials (3). ACI 548.8 (2) cautions against placing TPOs “over crack-fill materials that will affect the bonding or the curing of the overlay.” Moving cracks in the substrate will likely cause reflective cracking through the TPO. Synthetic fiber fabrics have been used over joints in segmental bridges, shown in Figure 15. TABLE 4 APPLICATION RATES FOR TPO COMPONENTS Overlay Multiple-Layer Epoxy Epoxy Slurry Methacrylate Slurry Premixed Polyester Thickness, mm (in.) 6.4 (1/4) 7.5 (5/16) 7.6 (5/16) 19.1 (3/4) Prime Coat, kg/m2 (lb/yd2) None 1.1 0.14 1.2 (2.0 ± 0.3) 0.41 ± 0.14/-0 (0.8 ± 0.3) 0.41 ± 0.14/-0 (0.8 ± 0.3) Layer 1 Resin, kg/m2 (lb/yd2) 1.1 ± 0.14 (2.0 ± 0.3) 6.0 ± 0.4 (9.8 ± 0.8) 2.7 ± 0.27 (5.0 ± 0.5) 5.29 ± 0.41 (9.8 ± 0.8) Layer 1 Aggregate, kg/m2 (lb/yd2) 5.4 ± 0.54 (10.0 ± 1.0) 6.5 ± 0.5 (12.0 ± 1.0) 6.5 ± 0.54 (12.0 ± 1.0) 38.6 ± 0.54 (71.0 ± 1.0) Layer 2 Resin, kg/m2 (lb/yd2) 2.2 ± 0.14 (4.1 ± 0.3) None None None Layer 2 Aggregate, kg/m2 (lb/yd2) 7.6 ± 0.54 (14.0 ± 1.0) None 7.6 ± 2.7 (14.0 ± 0.5) None Seal Coat Resin, kg/m2 (lb/yd2) None None 0.68 ± 0.14/-0 (1.3 ± 0.3) None Approx. Resin Content, % 25 25 24 13 Source: Sprinkel (15).

36 The test for strength based on the test method in ACI 503R (13) should be used to determine whether the cleaning procedure, that is, size of shot, flow of shot, traveling speed of machine, and number of passes, is adequate to provide the required minimum tensile bond strength. Figure 16 shows the setup for the tensile bond strength on a test patch of the installed overlay. For tensile bond strength of 1.7 MPa (250 psi) or a failure at a depth of 6 mm (0.25 in.) or more into the concrete substrate, greater than 50% of the area is required. The result is based on the average of three tests on each test panel, which is normally at least 0.3 m by 0.9 m (1 ft by 3 ft). Because the test is temperature sensitive, the test cannot be performed above 27°C (80°F). One test result (three tests on one patch) is required for each span or 418 m2 (500 ft2) of deck surface, whichever is greater. FIGURE 16 Pull-off test to determine suitability of surface preparation or bond strength of overlay. INSTALLATION METHODS Primers Primers, if required by the manufacturer, should be compat- ible with the concrete repair materials and the first resin coat to be applied. Multiple-Layer Overlays Figures 17 and 18 show where binder (resin or monomer sys- tem) needs to be sprayed, squeegeed, or broomed on to the deck surface and followed by broadcasting gap-graded aggre- gate to excess over the surface. Figures 19–21 show hand applications, chip spreader, and salting truck for applying aggregates. The aggregate must be allowed to spread out and fall downward into the resin, with the dust and fines carried off in the air. In hot weather, aggregate should be slowly and evenly built up on the surface until no wet spots are visible but before the resin begins to gel. 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 1.0 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.) FIGURE 17 Applying epoxy to deck for multiple-layer overlay. FIGURE 18 Brooming epoxy over surface. Slurry Overlays For MMA, a primer of monomer or resin system should be applied at a rate of 0.41 ± 0.14 kg/m2 (0.8 ± 0.3 lb/yd2) fol-

37 rate of 7.6 ± 0.27 kg/m2 (14.0 ± 0.5 lb/yd2). A binder seal coat of 0.68 ± 0.14 kg/m2 (1.3 ± 0.3 lb/yd2) is applied. The binder content is approximately 24% by weight of the over- lay (primer and seal coat). The thickness is about 7.6 mm (0.31 in) (6). Premixed Overlays Approximately 12% binder should be mixed with the aggregates. A primer is usually applied to the surface at a rate of 0.41 ± 0.14 kg/m2 (0.8 ± 0.3 lb/yd2) to improve the bond strength. The polymer concrete is placed and a vibra- tory screed is used to strike off and consolidate the PC. In some applications, continuous batching and paving equip- ment has been successfully used to place premixed PC. The thickness is about 19 mm (0.75 in.) The polymer concrete could be consolidated to a relative compaction of not less than 97% in accordance with California Test Method 551. Wood screeds can be used to obtain good surface texture in the form of transverse irregular ridges for premixed PC (34). A suitable skid resistance can be achieved by placing grooves in the fresh PC or by broadcasting aggregates onto the fresh PC surface (15). Figure 22 shows the finished sur- face of an overlay. FIGURE 22 Finished overlay surface. Material Handling, Mixing, and Placement Temperatures Handling and Mixing It is important that the handling and mixing of the resins and curing agents be performed in a safe manner that is accor- dance with the manufacturer’s written recommendations. Illinois DOT requires that resins be stored in their original containers inside a heated warehouse in a dry area with tem- peratures maintained between 16°C (60°F) and 32°C (90°F) Workers directly exposed to the resins are to wear protective gloves and goggles. Material Safety Data Sheets should be prominently displayed at the storage site, as per the Illinois lowed by a slurry mixture of 2.7 ± 0.27 kg/m2 (5 ± 0.5 lb/ yd2) of binder and 6.5 ± 0.54 kg/m2 (12 ± 1.0 lb/yd2) of man- ufactured-supplied filler. Gap-graded aggregate (as used in multiple-layer overlays) is broadcast onto the surface at a FIGURE 19 Hand application of aggregates over resin. FIGURE 20 Chip spreader application of aggregates. FIGURE 21 Salting truck for applying aggregates over epoxy.

38 2007 TPO specification. Hsu et al. (47) provide a summary of safety requirements for using chemicals for concrete- polymer materials. Michigan DOT indicates that if the in-place material is defective, it is usually because of improper proportioning or mixing. Using different colors for multicomponent systems helps to reduce proportioning errors (8). Missouri DOT has reported that an incorrect type of mix- ing paddle can lead to air bubbles in the epoxy, which results in pitting on the surface of the TPO. Harper (7) recommends that “jiffy” or “Sika” paddles be used. Placement Temperatures The temperature of placement is important. Not all DOTs specify a minimum temperature for placement; 10°C (50°F) to 16°C (60°F) is the range of minimum temperatures for epoxies reported by several DOTs. Some DOTs specify the same temperature for the deck and ambient; some use a slightly higher minimum temperature for the deck. Some DOTs specify the minimum temperature of the TPO com- ponents to be the same as the minimum ambient and/or deck temperature. North Carolina DOT recommends that the temperature be above 24°C (75°F). Harper (7) suggests that for bridges with steep grades or with super elevations, an upper limit on temperature be pro- vided to prevent the resin system from becoming too low in viscosity and ponding at the lowest elevation.

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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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