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Suggested Citation:"Chapter 1 - Background." National Academies of Sciences, Engineering, and Medicine. 2010. Evaluation and Repair Procedures for Precast/Prestressed Concrete Girders with Longitudinal Cracking in the Web. Washington, DC: The National Academies Press. doi: 10.17226/14380.
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Suggested Citation:"Chapter 1 - Background." National Academies of Sciences, Engineering, and Medicine. 2010. Evaluation and Repair Procedures for Precast/Prestressed Concrete Girders with Longitudinal Cracking in the Web. Washington, DC: The National Academies Press. doi: 10.17226/14380.
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Suggested Citation:"Chapter 1 - Background." National Academies of Sciences, Engineering, and Medicine. 2010. Evaluation and Repair Procedures for Precast/Prestressed Concrete Girders with Longitudinal Cracking in the Web. Washington, DC: The National Academies Press. doi: 10.17226/14380.
×
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Suggested Citation:"Chapter 1 - Background." National Academies of Sciences, Engineering, and Medicine. 2010. Evaluation and Repair Procedures for Precast/Prestressed Concrete Girders with Longitudinal Cracking in the Web. Washington, DC: The National Academies Press. doi: 10.17226/14380.
×
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Suggested Citation:"Chapter 1 - Background." National Academies of Sciences, Engineering, and Medicine. 2010. Evaluation and Repair Procedures for Precast/Prestressed Concrete Girders with Longitudinal Cracking in the Web. Washington, DC: The National Academies Press. doi: 10.17226/14380.
×
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Suggested Citation:"Chapter 1 - Background." National Academies of Sciences, Engineering, and Medicine. 2010. Evaluation and Repair Procedures for Precast/Prestressed Concrete Girders with Longitudinal Cracking in the Web. Washington, DC: The National Academies Press. doi: 10.17226/14380.
×
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Page 10
Suggested Citation:"Chapter 1 - Background." National Academies of Sciences, Engineering, and Medicine. 2010. Evaluation and Repair Procedures for Precast/Prestressed Concrete Girders with Longitudinal Cracking in the Web. Washington, DC: The National Academies Press. doi: 10.17226/14380.
×
Page 10
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Suggested Citation:"Chapter 1 - Background." National Academies of Sciences, Engineering, and Medicine. 2010. Evaluation and Repair Procedures for Precast/Prestressed Concrete Girders with Longitudinal Cracking in the Web. Washington, DC: The National Academies Press. doi: 10.17226/14380.
×
Page 11
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Suggested Citation:"Chapter 1 - Background." National Academies of Sciences, Engineering, and Medicine. 2010. Evaluation and Repair Procedures for Precast/Prestressed Concrete Girders with Longitudinal Cracking in the Web. Washington, DC: The National Academies Press. doi: 10.17226/14380.
×
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41.1 Problem Statement Precast/prestressed concrete girders are widely used in the United States for bridge construction. Longitudinal web cracks have been observed during prestress transfer, particularly at the ends of girders. With the use of higher strength concrete, deeper girders, and significantly higher prestress forces, these cracks are becoming more prevalent and, in some cases, larger. Reactions to these cracks have ranged from doing nothing to rejecting girders. Other reactions include debonding strands at the ends, reducing permissible prestress force, reducing allow- able compression stress at the time of transfer, injecting sealants into cracks, and coating the ends of girders with sealants. Clearly, there is no consensus on the causes of the longitudinal cracking and what level of longitudinal cracking is unacceptable. Concerns regarding end zone cracks are based on the possi- bility of having reduced structural capacity and future durabil- ity issues from strand corrosion. End cracks that run parallel with and intersect with the prestressing strands, reflecting strand locations, could cause debonding. This would result in lengthening of the transfer and development lengths, which may consequently reduce the shear and flexural capacity. Open cracks that travel along the strands and are exposed to chloride solutions may cause strand deterioration. Therefore, a thor- ough understanding was needed to determine whether longi- tudinal web cracks are of structural significance. If these cracks are not structurally significant, an understanding of whether they reduce durability was required. Although published guid- ance exists regarding acceptance and repair criteria, these doc- uments needed validation. The reader should be aware that the expressions longitudinal web cracking and end zone cracking are synonymous, and they are used interchangeably in this report. 1.2 Control of Cracking in Concrete Structures Cracking of concrete structures has been the focus of researchers for decades. A review of the literature has shown that crack width has been the most common measure used to quantify acceptable levels of cracks in reinforced concrete structures. The majority of the cracking studies were con- ducted to investigate flexural cracking in reinforced concrete beams. Flexural cracks are formed on the tension side of a beam, typically at right angles to the reinforcing bars. They largely depend on the concrete cover, level of stress in the steel reinforcement, and distribution of the reinforcement. The majority of the studies concentrated on providing informa- tion on sources of cracking, factors affecting crack width, and formulas used to estimate crack width. Some information on cracking due to other effects—such as shrinkage, temperature, and alkali silica reaction—also was found in the literature. However, only a small amount of infor- mation on the effects of web cracking due to prestress release in member ends was found. Web end cracking is most severe when the product is lifted off the bed. The cracks tend to get smaller and sometimes totally disappear as the vertical gravity loads are introduced by superimposed loads and support reac- tion. When these cracks are diagonal, they are “normal” to that of the compression struts created by the shearing effects and, thus, are not additive to the principal tensile stresses due to shear. When diaphragms are used, the most severe cracks at the member ends are partially enclosed in the diaphragm concrete. Thus, it appears to be logical to have less restrictive cracking limitations on web end cracking than on conventionally rein- forced concrete sections subject to flexure. 1.2.1 Evolution of Permissible Crack Widths The evolution of, and recommendations for, permissible crack widths developed between 1935 and 1970 can be traced from several references (1–6). A summary of the recommen- dations from these publications is compiled in Table 1.1. It should be noted that the majority of these recommendations were based on flexural cracking in beams. The statistical repre- sentation of these recommendations showed that the flexural crack width in beams, at 40 ksi tensile stress in reinforcement C H A P T E R 1 Background

5Table 1.1. Permissible crack widths developed between 1935 and 1970.* Source Maximum Crack Width (in.) Conclusion or Exposure Level Notes N.J. Rengers, 1935, as contained in Reference 1 ≤ 0.012 0.012–0.04 0.040–0.080 - Tolerable crack width - Excessive crack width - Some corrosion danger Only one specimen tested. Abeles, 1937, as contained in Reference 1 0.012–0.016 - Present no danger of rusting Provided there are no special chemical influences. Tremper, 1947, as contained in Reference 1 0.005–0.050 - Cracks of fairly large widths in a sound concrete will not promote serious corrosion of the reinforcement Sixty-four concrete blocks were exposed to a marine environment for 10 years. Brocard, 1957, as contained in Reference 1 0.004 0.024 - Corrosion was not appreciably accelerated. - Corrosion rate increased by a factor of 5 to 10. The reinforcement consisted of thin walled steel tubes embedded in concrete prisms. Engel and Leeuwen, 1957, as contained in Reference 1 0.008 0.012 - Unprotected structures (external) - Protected structures (internal) Recommendations are made from investigations of structures existing for more than 15 years. Brice, 1957, as contained in References 2 and 7 0.004 0.008 0.012 - Severe exposure - Aggressive exposure - Normal exposure Flexural cracking in beams. Rusch, 1957, as contained in References 2 and 7 0.008 0.012 - Aggressive (salt water) - Normal exposure Flexural cracking in beams. Etsen, 1957, as contained in References 2 and 7 0.002–0.006 0.006–0.010 0.010–0.014 - Severe to aggressive - Normal exposure (outside) - Normal exposure (inside) Flexural cracking in beams. Voellmy, 1958, as contained in Reference 1 0.008 0.008–0.020 > 0.020 - No corrosion occurred - Slight corrosion at isolated regions - More localized corrosion Cracked beams were exposed to the atmosphere for 10 years. The locations varied from rural to industrial areas. Bertero, 1958, as contained in Reference 1 0.001–0.006 0.010–0.014 - Exposure to seawater, smoke, etc. - Indoor exposure These allowable crack widths apply to structural elements under permanent loading with 1-inch cover. Haas, 1959, as contained in Reference 1 0.008 0.012 > 0.012 - Exposed structures (external environment) - Protected structures (internal environment) - Permissible in the absence of heating, humidity, and other aggressive conditions These values are applicable only in cases where the reinforcement is adequately covered and where the loads are permanent. Shalon and Raphael, 1959, as contained in Reference 1 < 0.008 0.008 - Structures exposed to saline air - Exposed structures Hendrickson, as contained in Reference 1 0.010 - Acceptable limit for reinforced concrete pipes Crack widths smaller than 0.01 in. may often close by means of autogenous healing and therefore present little danger of severe corrosive attack. ACI 1963 Building Code, Section 1508, as contained in Reference 1 0.010 0.015 - Exterior members - Interior members Determined by tests on actual full- scale flexural members CEB, 1964, as contained in References 5 and 7 0.004 0.008 0.012 - Interior or exterior, aggressive and watertight - Aggressive - Normal Flexural cracking in beams. DL Causes Compression and LL Causes Tension 0.008 0.008 0.010 0.012 - Seawater and seawater spray, alternate wetting and drying - Deicing chemicals, humidity - Salt, air water and soil - Air or protective membrane DL and LL Cause Tension U.S. Bureau of Public Roads (Maximum crack width at steel level under service load), 1966, as contained in References 6 and 7 0.006 0.006 0.008 0.010 - Seawater and seawater spray, alternate wetting and drying - Deicing chemicals, humidity - Salt, air water and soil - Air or protective membrane Flexural cracking in beams. *Permissible crack widths provided in this table are taken from References 1 through 6.

6Table 1.2. Tolerable crack widths in reinforced concrete structures (7). Exposure Condition Tolerable Crack Width, in. (mm) 1. Water-retaining structures (excluding non-pressure pipes) 2. Seawater and seawater spray, wetting and drying 3. Deicing chemicals 4. Humidity, moist air, soil 5. Dry air or protective membrane 0.004 (0.10) 0.006 (0.15) 0.007 (0.18) 0.012 (0.30) 0.016 (0.41) Table 1.3. Tolerable crack widths in reinforced concrete structures (8). Exposure Maximum Crack Width at Extreme Tensile Fiber of the Concrete Section (in.) 90th Percentile of the Maximum Crack Width (in.) Appearance Severe: Corrosive gasses or soils Corrosive industrial or maritime environment 0.0012 0.004 Moderate: Running water Inclement weather without aggressive gasses 0.0160 0.008 Difficult to see with the naked eye Mild: Conditions where high humidity is reached for a short period in any one year 0.0200 0.012 Easily visible bars, ranged from 0.0025 to 0.016 in, with the majority of the results ranging from 0.005 to 0.010 in. In the early 1970s, Committee 224 of the American Con- crete Institute published the first edition of the ACI 224 report, Control of Cracking in Concrete Structures, which give principal causes of cracking in reinforced/prestressed concrete and recommended crack control criteria and procedures (7). Since then, the report has undergone several revisions. The report discusses many possible sources of cracking, such as shrinkage cracking, flexural cracking, tension cracking, and end zone cracking on prestressed concrete members. The report gives the following guidelines, shown in Table 1.2, for tolerable crack widths at the tensile face of reinforced concrete structures for typical conditions. The report recommends that these values of crack width are not always a reliable indication of steel corrosion and deterioration of concrete to be expected. The report states that engineering judgment should be exer- cised and other factors, such as concrete cover, should be taken into consideration to revise these values. Although the report does not give any guidelines on tolerable crack size specifi- cally for end zone cracking in pretensioned members, it can be interpreted from the report that the limits presented in Table 1.2 are applicable to all types of cracks regardless of their source. The report states the importance of proper design of the bursting reinforcement, and that the first row of the bursting reinforcement should be placed as close as possible to the member end and the rest should be distributed over a certain distance. In 1975, CEB Eurocode No.2 (8) developed limits for cracks developed in beams under flexure and concrete members under direct tension, see Table 1.3. The limits given in Table 1.3 were developed based on envi- ronmental criteria. A summary of the CEB procedure to check bar spacing to control the crack width can be found in Reference 9. In this paper, the author recommended that the maximum crack width be limited to 0.008 in. to avoid any concerns by casual observers and the public. In 1983, the PCI Committee on Quality Control Perfor- mance Criteria developed a report on Fabrication and Shipment Cracks in Prestressed Hollow-Core Slabs and Double Tees (10). The report provides a collection of various cracks that may occur in hollow-core slabs and double tees during casting, stripping, or shipping. The objectives of the report are to help precast producers and design engineers identify possi- ble sources of cracking and make decisions on the accept- ability of the product. The report recognizes end-of-beam cracking as follows: • For hollow-core slabs the report provides two types of web cracking that may occur at prestress release due to the burst- ing forces. The first type is above the strands and the second type is at or near the strands, as shown in Figure 1.1(a) and 1.1(b), respectively. The report states that the crack width of the first type can range from a hairline up to 0.25 in. (6.3 mm). However, it does not provide a crack width for the second type. The report states that these cracks can

reduce shear capacity, but it does not give any criteria on when to reject the product. The report gives some repair procedures that range from epoxy injection for small cracks to solid grouting of the voids. • For double tees the report recognizes horizontal end crack- ing in the stem during prestress release, as shown in Fig- ure 1.2. It states that the crack length can extend horizontally for a distance of from several inches to a few feet. However, the report does not give any guidelines regarding the crack width or when to reject the product. The report states that if the crack plane coincides with a strand, it may affect the bond between the strand and concrete and increase trans- fer and development length. In 2006, the Precast/Prestressed Concrete Institute (PCI) published the Manual for the Evaluation and Repair of Pre- cast, Prestressed Concrete Bridge Products (11). The objective of the report is to achieve a greater degree of uniformity among owners, engineers, and precast producers with respect to the evaluation and repair of precast, prestressed concrete bridge beams. The report recognizes end-of-beam cracking in “Troubleshooting, Item #4.” A summary of the report find- ings and recommendations are as follows: • For cracks that intercept or are collinear with strands but without evidence of strand slippage (significant retraction of strand into the beam end), the report recommends inject- ing the cracks with epoxy. • The report uses the crack width values developed in ACI 224R-01 as guidelines whether or not to inject cracks. These values are shown in Table 1.4. • For cracks that intercept or are collinear with strands with evidence of strand slippage (significant retraction of strand into the beam end), the report recommends injecting the cracks with epoxy and re-computation of stresses after shift- ing the transfer and development length of affected strands. • The report recognizes the fact that this type of cracking does not grow once the beam is installed on a bridge. On the contrary, the cracks will close to some extent due to applied dead and live loads, as end reactions provide a clamping force. • The PCI report does not give any guidelines on when to reject a beam with end cracks. More information on the permissible crack width is pro- vided in Appendix A, Literature Review, of this report. 1.2.2 Sources of End Zone Cracking Longitudinal end zone cracking occurs in pretensioned girders during release of the pretensioned strands. The draped strands are usually released first using flame cutting at the ends and then by removing the hold-down anchorage devices at the harp points. The straight strands are then released by one of the following two methods (1) flame cutting, which is a practice used by a large number of precast producers, or (2) gradual release (jack down) in which the abutment of the prestressing bed is equipped with a hydraulic system that allows it to move gradually towards the concrete member. During release, the strands grip against the concrete, grad- ually transferring their force to the concrete girder through a distance known as the transfer length. The force transferred from the strands causes member shortening. The member slides on the bottom pallet, dragging the ends at the bottom. The horizontal sliding is accompanied by upward camber, and the precast member becomes supported at its ends only. The release process is typically accompanied with forma- tion of longitudinal cracks at the girder ends. These cracks may occur in the web or at the junction between the web and the bottom flange. There are many possible sources that may 7 Figure 1.1. End-of-member cracks for hollow-core slabs. (a) Above the Strands (b) At or Near the Strands Figure 1.2. End-of-member cracks for double tees. Table 1.4. End-of-beam cracks that should be injected (11). Exposure Condition Crack Width, in. (mm) 1. Concrete exposed to humidity 2. Concrete subject to deicing chemicals 3. Concrete exposed to seawater and seawater spray, wetting and drying cycles > 0.012 (0.30) > 0.007 (0.18) > 0.006 (0.15)

8increase or decrease the likelihood of this longitudinal end zone cracking in pretensioned girders. Within the literature search and the survey responses, the following multiple sources were suggested: • Method of detensioning: As previously explained, the bottom strands can either be flame cut manually while still fully tensioned, or they can be slowly jacked down by a hydraulic release before being cut. Since flame cutting is done manually, the strands are released individually, which creates uneven forces throughout the beam and presents a more localized aggressive introduction of force to the beam. Slowly jacking down the strands prevents the sudden introduction of force that flame cutting causes and gives the concrete girder more time to accommodate the transformed compressive force. Although hydraulic release is preferred to reduce end zone cracking, very few state departments of transportation (DOTs) mandate its use because it requires the precast plants to restructure the existing prestressing beds. • Release of the top straight or draped strands before the bottom straight strands: This sequence puts the bottom flange in tension (especially with deep precast members), trying to stretch it out. Since the beam at this stage is in full contact with the bottom form of the prestressing bed, and its bottom flange is restrained by the straight strands that are not released yet, the frictional force produced at the bot- tom surface of the member resists this movement and may produce a vertical crack at the side of the bottom flange that extends vertically towards the web/bottom flange junction. In order to treat this problem, some state DOTs require not to fully tension strands located in the top flange, reduce the height of the draped strands to the level that makes release stresses within their allowable limits, and/or uniformly dis- tribute the draped strands across the web height rather than concentrating them close to, or in, the top flange. • Order of release of bottom strands with the flame cut- ting method: Due to limited accessibility of interior strands, the edge strands on each layer are generally released before the interior strands. This order puts the tips of the bottom flange in compression and makes them act as free cantilevers, which initiates horizontal cracking at the web/bottom flange junction or sloped cracks in the web close to its junction with the bottom flange. A specific pattern must be fol- lowed in order not to increase cracking. Angular cracks can occur from the stress difference of cut and uncut pre- stressed strands if the cutting pattern is not idealized. Both ends of the same prestressing strand should also be cut simultaneously to prevent uneven forces. However, researchers found that the sudden introduction of stress into the girder from flame cutting of the strands is conducive to cracking, even with a planned pattern (12–13). • Length of the free strand in the prestressing bed: As the first strands are cut and the precast member is compressed caus- ing elastic shortening, the remaining uncut strands must lengthen to accommodate the shortening of the member. The resulting tensile force in the uncut strands causes ver- tical cracks to form near the ends of the member, where the compression from the cut strands has not been fully imparted on the section. This source can be very detrimen- tal in cases where more than one precast member is cast on a single prestressing bed. In a study conducted in 1978 (12), researchers found that this source of cracking can be eliminated by making the free strand length between the abutment and the concrete member or between adjacent members as short as needed for fabrication. • Friction with the bottom form of the prestressing bed (11, 14): In cases where the bottom form of the prestress- ing bed is not properly oiled or has indentions, horizontal cracks are developed in the bottom flange. When cutting the strands the beam may be moved horizontally along the bed floor, causing friction on the surface between the con- crete and steel. • Heat concentration during flame cutting (11, 15): It was reported that concentrated heating of a strand leads to high sudden shock of the released prestress force. It is always recommended to heat the strand over a long distance to allow slow elongation (annealing), and that flame cutting of strands be done by trained and experienced workers. • Lifting the precast member from the bed (16): The pre- stressing force causes the girder to camber so that the cen- ter of the beam is forced higher than the ends. Shortly after prestress release, the precast member is lifted from the bed and moved to the storage area. In most cases where the member is relatively long, the lifting points are generally recessed by as much as 15 to 20 ft from the member ends, at camber raised locations. The lifting point locations are subject to negative moments not only from the prestress but also from the self weight. This latter effect is often ignored by designers. It is a major contributor to the temporary crack widening that occurs at the time of lifting. At this initial lifting of the beam, the prestress force has not yet diminished and is at its highest while the concrete has not yet reached its full strength. It has been known to con- tribute to downward diagonal cracks in the upper part of the web. • Hoyer Effect (17): Upon release of the prestress, the diam- eter of the strand expands and pushes against the surround- ing concrete. This action, which is known as the Hoyer Effect, improves the bond between the strand and the con- crete and helps in transferring the prestress force to concrete. However, it creates radian tensile stresses in the concrete volume, which leads to a radial crack that extends from the strand to the nearest concrete surface at the end sur-

face of the member. This type of cracking generally would be controlled with bottom flange confinement of the con- crete around the strands. • Use of large strands: With the increasing use of concrete with high strength, a number of state highway agencies have begun using 0.6-in. diameter strands at the standard 2-in. spacing in place of the conventional 0.5-in. diameter strands. Also, a demonstration project by the Nebraska Department of Roads is under way to implement the use of 0.7-in. strands on the Pacific Street overpass over Inter- state I-680 in Omaha. A full-scale specimen was fabricated for the University of Nebraska research team. The spec- imen, an NU 900 (36-in. deep) I-girder was prestressed with twenty-four 0.7-in. strands at 2.2 in. horizontally and 2.25 in. vertically. This prestress was the same amount required for a two-span bridge, 100-ft span, 10-ft, 10-in. spacing. Previous research at the university established that cracks are more extensive with the larger 0.6-in. and 0.7-in. strands than with the 0.5-in. strands. • Inadequate design of end zone reinforcement: Increased vertical reinforcement concentrated at the ends of the girder has been shown to reduce the lengths and widths of end zone cracks. Therefore, insufficient amounts of end rein- forcement or misplacement of the bars too far away from the edges may increase the amount of cracking experienced. Also, the lack of confinement stirrups around the prestress- ing strands may increase cracking. It should be noted that the end zone reinforcement is not presented to eliminate end zone cracking but to control it. • Concrete type: Lightweight concrete has a reduced tensile strength capacity and modulus of elasticity, and is there- fore less able to withstand the extreme prestressing forces. This leads to longer, wider, and a larger quantity of crack- ing along the ends. • Low concrete release strength: The concrete must be allowed to set and cure long enough to reach certain strength before release. This strength value, known as the minimum release strength, assures that the concrete is strong enough to handle the prestressing forces. If the concrete does not reach this strength, it may be too weak to resist the prestress- ing forces, leading to cracking. • Strand distribution: Girders with a large number of draped strands appear to have more extensive cracking than girders with fewer or no draped strands. The concentration of the prestressing force at the top of the web and the bottom flange increases the bending of the section and the vertical tensile stresses. Other proposed variables related to end zone cracking include form geometry, beam length, the number of strands, thermal and shrinkage stresses, the number of debonded strands and the debonding lengths, residual stress from cur- ing, restraint of forms during curing, and using forceful means to remove the side forms and bulkheads. From the survey responses, the most commonly cited cause was strand distribution (72%), and the second most commonly cited cause was detensioning (50%). More discussion on sources of end zone reinforcement is given in Appendix A, Literature Review, of this report. 1.2.3 Design of End Zone Reinforcement Design of end zone reinforcement details is typically done by (1) estimating the bursting force (vertical tensile force developed at ends of pretensioned precast concrete girders during prestress release) as a percentage of the total prestress- ing force just before release, (2) setting a limit on the stress of the required end zone reinforcement that allows the designer to control the size of the cracks and keeps them within accept- able limits, and (3) providing a scheme on how to distribute the end zone reinforcement. A literature search has shown that most of the design meth- ods require that the end zone reinforcement be designed to resist about 4% of the total prestressing force at transfer, and that the reinforcement must be designed for a service stress not exceeding 20 ksi. However, there is no agreement on how to distribute this reinforcement in the end zone areas. For example, Article 5.10.10.1 of the AASHTO LRFD specifications (18) states that it should be located within h/4 (one-fourth of the depth of the girder) from the end of the girder, while recent research conducted by the University of Nebraska (16), and adopted by Alberta DOT, Canada, has recommended that 50% of this reinforcement should be placed h/8 (one-eighth of the depth of the girder) from the end of the beam and the remainder should be placed between h/8 and h/2 from the end. In addition to the disagreement on the distribution of the end zone reinforcement, some highway authorities require a specific way of anchoring the end zone reinforcement. For example, the Illinois Department of Transportation (IDOT) requires that the end zone reinforcement should be made of 3⁄4-in. diameter threaded rods that are welded to a 1-in.-thick plate embedded in the bottom flange, as shown in Figure 1.3. Also, the threaded rods are anchored at the top surface of the girder through a 3⁄4-in.-thick plate with nuts. Another exam- ple is the bursting reinforcement detail recommended and used by Central Pre-Mix Prestress Co. of Spokane, Washing- ton, where a single #8 bar that travels vertically through the center of the girder is bent back into the interior of the beam at both the top and bottom, as shown in Figure 1.4. More discussion on end zone reinforcement details used by various highway authorities is given in Appendix A, Liter- ature Review, of this report. 9

1.3 Methods and Materials Used for Repair The following three methods of repair were found in the literature review: 1. Epoxy injection, 2. Batching and sealing the cracks, and 3. Sealing the cracks. Use of any of these methods depends on the crack width and criteria used by the highway authorities. 1.3.1 Epoxy Injection Procedure by PCI Manual for the Evaluation and Repair of Precast, Prestressed Concrete Bridge Products The PCI Manual for the Evaluation and Repair of Precast, Prestressed Concrete Bridge Products (11) provides detailed information on the process and steps used in the epoxy injec- tion of cracks in precast, prestressed concrete bridge prod- ucts. The responses to the national survey that was conducted in this research project have shown that this manual is cur- rently used by many state DOTs and precast producers for repair of end zone cracking. Chapter 4 of the PCI publication states that the epoxy injection procedure applies to cracks that are wider than 0.006 in. or to cracks that are noticeable after soaking with water. The publication provides the epoxy injection procedure for two cases (1) cracks accessible and visible from both sides, and (2) blind cracks that are not vis- ible or accessible from both sides. Chapter 5 of the same pub- lication provides information on how to prepare these cracks. It also states that 75 psi to 200 psi injection pressure is com- monly used for crack widths in the range of 0.006 to 0.007 in. 10 Figure 1.3. End zone reinforcement detail used by IDOT. Figure 1.4. End zone detail used by Central Pre-Mix Prestress Co., Spokane, Washington. #8 Bar Elevation End View

1.3.2 Batching Materials and Sealants Batching materials typically are used to fill the cracks but not to restore the concrete tensile strength at the cracks; sealants are used to create impermeable concrete surfaces that prevent moisture from getting into the girders and causing corrosion of the reinforcement. A wide range of commercial batching materials and sealants are available in the market. Precast pro- ducers make their choice based on experience and performance of the selected material. Appendix A of this report provides some examples of batching materials and sealants used by precast producers in Nebraska and Washington State. 1.4 Objective and Scope of the Research The NCHRP objective of this project is stated as follows: To establish procedures for the acceptance, repair, or rejec- tion of precast/prestressed concrete girders with longitudinal web cracking. A user’s manual for the application of these pro- cedures will be prepared based on the research findings. The research team also attempted to include as many of the following related objectives as practicable, without interfering with the accomplishments stated in the primary objective: 1. Develop limits for cracking that can not be tolerated, result- ing in product rejection. 2. Develop repair methods for cracking that is tolerable but must be repaired before the girder is used. 3. Develop guidelines for cracks that are not required to be repaired. These guidelines must be based on both initial and long-term performance and on the potential for re- inforcement corrosion or further crack propagation. This objective must focus on how the girders are used and in what environmental conditions. 4. Develop a user’s manual for acceptance criteria and repair materials and methods at the precast plant. Repair materi- als and methods must be validated before they are included in the manual. 5. Develop improved crack control reinforcement details for use in new girders. 6. Propose revisions to the AASHTO LRFD Bridge Design Specifications as warranted. To accomplish these objectives, the following tasks were performed: Task 1. The research team reviewed and interpreted U.S. and international practices, performance data, research findings, and other information related to the types, causes, mitigation, evaluation, and acceptance or repair of longitu- dinal web cracking in precast/prestressed concrete girders. In addition to the literature review, a national survey was developed to collect information on the experience regard- ing longitudinal end zone cracking. The national survey was sent to all state DOTs, other owner agencies, selected bridge consultants, and precast concrete producers. It was also sent to about 150 PCI bridge product producers, the PCI Com- mittee on Bridges, the PCI Bridge Producers Committee, and selected Canadian agencies. The questionnaire included questions on reinforcement details, strand release process, criteria for repair and rejection of cracked members, and repair methods. Task 2. Using information assembled in Task 1, the factors that alone or in combination may initiate or propagate lon- gitudinal web cracking were identified and documented. Task 3. Using the findings from Tasks 1 and 2, the research team proposed evaluation criteria for assessing the strength and durability consequences of longitudinal web cracking. The evaluation included consideration of when repairs are required and what repair methods are appropriate. Task 4. The research team prepared a future work plan to develop and validate the evaluation criteria and repair methods proposed in Task 3. Task 5. Tasks 1 through 5 were conducted within four months of the contract start and an interim report, doc- umenting the results of Tasks 1 through 4, was developed and submitted to NCHRP for review. The report in- cluded the future work plan envisioned by the research team to reach the project objectives (Tasks 6 through 8). Two months were given to the members of the project panel to review the interim report. Then, the research team had a meeting with the panel to discuss their comments on the interim report and future work plan. Based on this meet- ing, a modified version of the future work plan was devel- oped by the research team and submitted to NCHRP for final approval. Task 6. Based on the results collected from Task 6, the re- search team prepared a manual for the acceptance, repair, or rejection of precast/prestressed concrete girders with longitudinal web cracking. The manual went through sev- eral revisions based on the comments received from the project panel. Task 7. The research team developed a final report describ- ing the entire research effort. 1.5 Applicability of Results to Highway Practice The project was structured to provide a manual of pro- cedures for the acceptance, repair, or rejection of precast/ prestressed concrete girders with longitudinal web cracking. The manual, which is provided in Chapter 3 of this report, can 11

be used by highway authorities to develop their own crite- ria for acceptance or rejection. The information provided in Appendices A and B also can provide the decision maker with a clear view of possible sources of longitudinal web cracking, available reinforcement details used to control longitudinal web cracking, and acceptance/rejection criteria used by other highway authorities. 1.6 Organization of the Report This report consists of four chapters and seven appendices, as follows: • Chapter 1 provides the problem statement, current knowl- edge of the problem, research objectives, and scope of the research, and applicability of results to highway engineering practice. • Chapter 2 summarizes the approach developed by the research team to reach the objectives of the project. • Chapter 3 provides information on the project activities and findings, which include (1) a summary of results of the national survey, (2) full-scale testing of eight girders, (3) a durability test, which included three phases, (4) a manual of procedures for the acceptance, repair, or rejec- tion of precast/prestressed concrete girders with longi- tudinal web cracking, and (5) recommended end zone reinforcement detail. • Chapter 4 summarizes the significant conclusions of this project and suggestions for future research. The following appendices are not published herein. To find Appendices A through G for this report, go to www.trb.org and search for “NCHRP Report 654”. • Appendix A provides a summary of the information col- lected from the literature review and national survey. • Appendix B provides the national survey and its responses. • Appendix C provides information on the full-scale girder test regarding fabrication, testing, and analysis of test results. • Appendix D provides information on the sealants that were used in the durability testing. • Appendix E provides the ASTM Specifications used in the durability testing. • Appendix F provides information on the field inspection of bridges in Nebraska and Virginia. • Appendix G provides design examples of end zone rein- forcement using the LRFD Specifications and the proposed details. 12

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 654: Evaluation and Repair Procedures for Precast/Prestressed Concrete Girders with Longitudinal Cracking in the Web explores the acceptance, repair, or rejection of precast/prestressed concrete girders with longitudinal web cracking. The report also examines suggested revisions to the American Association of State Highway and Transportation Officials’ Load Resistance Factor Design Bridge Design Specifications and measures to develop improved crack control reinforcement details for use in new girders.

Appendices A through G for NCHRP Report 654 are available online.

Appendix A—Literature Review

Appendix B—National Survey

Appendix C—Structural Investigation and Full-Scale Girder Testing

Appendix D—Sealant Specifications

Appendix E—ASTM Specifications

Appendix F—Field Inspection of Bridges

Appendix G—Design Examples of End Zone Reinforcement

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