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27Â Â An online-based survey was distributed to the 50 state departments of transportation in Feb- ruary 2020. Initial survey distribution occurred that month, with subsequent attempts to contact agencies to gather as many responses as possible. The survey (included in the appendix) gathered information on the state transportation agencyâs experience with post-tensioned bridge system design, construction, maintenance, inspection, and repair. All 50 of the DOTs responded to the survey (see FigureÂ 7). Five responses were partial or incomplete. One state (Illinois) opted not to participate, citing lack of relevant experience; however, this notification was counted as a survey response. This chapter covers findings and trends from the survey and subsequent communica- tions with state DOT personnel. Experience Forty-four state agencies report having post-tensioned structures in their inventory (see FigureÂ 8). Six respondents do not have post-tensioned structures (Arkansas, Iowa, Maryland, South Dakota, Tennessee, and Wyoming). The states without post-tensioned bridge structures provided several reasons for not building PT structures, including lack of familiarity, concerns regarding quality and durability, lack of need, and lack of a local, established industry presence. Of the state DOTs without PT structures, several communicated no anticipated future need for such a structure. Twenty-three states report having conducted repairs on their PT structures (see FigureÂ 9); more than half of the state DOTs with PT structures have performed some type of repair. The structure types included in state DOT inventories varied widely (see FigureÂ 10). No attempt was made to quantify the number of structures of each type in state inventories. Segmental bridge structures are found in a majority of the states with PT structures in their inventory, with 24 states having cast-in-place segmental structures and 30 states having precast segmental structures. Half of all states have PT decks (25), PT pier caps (27), and PT spliced girders (25). States described âotherâ types of PT structures in their inventory as â¢ Hybrid pretensioned, post-tensioned girders (Alaska) â¢ Precast channel units (Alabama built some in the 1970s; New York built with a patented channel shape starting in the 1990s) â¢ Columns, U-beams, straddle beams, C-piers, footings (Florida) â¢ Precast panel slab bridges with transverse PT bars (a significant quantity built in the 1970s and 1980s and discontinued because of poor performance, Louisiana) â¢ Hold-downs at end piers (Ohio) â¢ Arch ribs (Oregon) â¢ Retaining wall tie-backs for soldier pile walls, sheet pile walls (Wisconsin) C H A P T E R 2 Survey
28 Repair and Maintenance of Post-Tensioned Concrete Bridges Figure 7. Survey participation by state DOTs. Figure 8. States with post-tensioned bridge structures.
Number of States 0 10 20 30 40 50 Have performed repairs Have PT structures 23 44 Figure 9. States with post-tensioned bridge structures and with repair experience. N um be r o f S ta te s Have in Inventory Have Performed Repairs Figure 10. Post-tensioned structures, by type.
30 Repair and Maintenance of Post-Tensioned Concrete Bridges States have performed repairs on every type of PT structure (see FigureÂ 10). Adjacent pre- cast box-girder structures were not covered by the survey; the reader is referred to NCHRP Synthesis 393 for information on this topic (Russell 2009). Design and Construction A series of questions in the survey were aimed at identifying efforts by state agencies to ensure current, up-to-date practices during construction and design. These included questions related to agenciesâ PT-specific specifications (if any), the inclusion of protection levels in design approach, and quality control/assurance practices during construction. In general, a uniformity in approach is not apparent, with a variety of guidance documents referred to, certification programs specified, and quality control/assurance and design approaches used. This is not surprising, given the wide range of PT experience from state to state (see FigureÂ 11), with some states having nearly 3,000 PT structures (California) and others having five or fewer (Delaware, New York, Rhode Island, South Carolina). Agencies were asked to specify reference documents used in developing their specifications. In general, state specifications are informed from guidance documents such as the PTI/ASBI M50 Guide Specification for Grouted Post-Tensioning, the PTI M55 Specification for Grout- ing of Post-Tensioned Structures, and the AASHTO-LRFD Bridge Construction Specification. A notable number of state DOT agencies are modeling their post-tensioning practices on specifications and actions from key states, most often Florida (referred to by seven states: Alaska, Louisiana, Minnesota, New Hampshire, Ohio, Oklahoma, and South Carolina) and California Number of PT Structures N um be r o f S ta te s 0 4 8 12 16 0 Over 500 6 15 14 4 5 4 1 1-10 11-50 51-100 101-200 201-500 Figure 11. Quantity of PT structures in inventory.
Survey 31Â Â (referred to by four states: Alaska, Arizona, Hawaii, and Nevada), in the development of their PT specifications. Other states were referring to a neighboring state; states referred to in this vein include Massachusetts (referred to by New Hampshire and Rhode Island), Washington (referred to by Idaho), and Vermont (referred to by New York). A few state agencies are relying on project-specific specifications for their post-tensioned work (Louisiana, for example). Most state DOTs have updated their PT specifications in the last 2 to 7Â years. Given this effort, and the fact that many states (14) are referring to PTI/ASBI M50 Guide Specification for Grouted Post-Tensioning and PTI M55 Specification for Grouting of Post-Tensioned Structures in their specification updating, it appears that the lessons learned since the grout problems uncovered in the early 2000s are making their way into DOT guidance documents, though not universally. Additional efforts to ensure nationwide awareness of improved practices for PT construction may be warranted. The survey asked state DOTs to identify if a specific protection-level design approach was required for their PT structures. The International Federation for Structural Concrete (fib) and the PTI M50 document suggest a tiered approach to strategize the design of the corrosion pro- tection system for a post-tensioned structure (see FigureÂ 4 and TableÂ 1). A structure is designed with a designated protection level (PL), which guides the design of protective elements. The PL is selected on the basis of the exposure of the structure and the aggressiveness of the struc- tureâs environment (see FigureÂ 4). The concept of designing for a particular protection level is accomplished either through explicitly naming a PL-requirement (done by some states) or by requiring the same protective elements. In interpreting the survey responses, it is important to note that the concept of designing for a particular protection level may be new to a stateâs specifications; no effort was made to identify when states included âPLâ considerations in their specifications. Most states (23) with PT structures in their bridge inventory do not indicate a design requirement for a particular protection level of their post-tensioned structures (see FigureÂ 12). Only some states are specifyingâeither directly or through equivalent requirementsâa par- ticular protection level. Michigan is requiring the most stringent protection methods for its Number of States 0 5 10 15 20 25 None specified Project-specific PL-3 PL-2 PL-1B PL-1A 23 3 1 5 1 0 Figure 12. Protection levels for PT structures.
32 Repair and Maintenance of Post-Tensioned Concrete Bridges PTÂ structures, PL-3. Five states (Louisiana, Minnesota, Mississippi, New York, and Rhode Island) are specifying PL-2, although Minnesota notes that it has been unsuccessful in imple- menting appropriate duct couplers to satisfy PL-2 in its precast segmental projects. Colorado is implicitly using PL-1B by requiring the same components. Nebraska, Pennsylvania, and Wisconsin are specifying protection levels on a project-by-project basis, using the particular structureâs exposure as a consideration in the assigned protection level. To identify how many states are formalizing the qualifications of PT installers, agencies were asked to identify their requirements for PT installer qualifications/certifications (see FigureÂ 13). It is important to note that states may specify more than one certification in their requirements, and that certifications are role dependent. Twenty-one states require the ASBI grouting certi- fication. Seventeen states require installers to have the PTI Level 2 installer certification, with another 10 requiring the PTI Level 1 certification. Five states have âotherâ requirements (for example, in Florida, the stateâs DOT-specific Construction Training and Qualification Program, CTQP) to become a qualified grouting technician. The FDOT CTQP qualifications for grout/PT installation can be partially satisfied with the ASBI grouting certification and PTI certification, respectively. States were asked to indicate what types of personnel perform both quality assurance and quality control on their post-tensioned structures, selecting all that applied (see FigureÂ 14). Most states are relying on a combination of in-house staff and consultant engineering inspectors to perform quality assurance tasks. Repairs A majority of states (23) with PT structures in their inventories (44) have experience with PT repair (see FigureÂ 15). Repairs (in general, not just PT repairs) are most often performed by con- tractors (31), especially in cases with extensive repair. Some states occasionally perform repairs with in-house staff (New Hampshire and Oregon), though these states also use contractors. 5 17 10 21ASBI grouting certification PTI Level 1 installer PTI Level 2 installer Other Number of States 0 5 10 15 20 25 Figure 13. State requirements for PT installer qualifications/ certifications.
Survey 33Â Â Consultant inspection (CEI)In-houseContractor N um be r o f S ta te s 0 5 10 15 20 25 30 Note: QA = quality assurance; QC = quality control. Figure 14. Personnel performing quality assurance and quality control. Figure 15. Experience with PT repair by state.
34 Repair and Maintenance of Post-Tensioned Concrete Bridges Additional questions were aimed at identifying trends among repair occurrences and potential causes (see FigureÂ 16). Seventeen states have conducted repairs to PT systems during construc- tion. Ten states have performed repairs to address corrosion issues. Nine states have performed repairs of or have replaced a deck on a PT bridge. One state (Hawaii) has performed repairs to a PT bridge following a vehicle impact. Though it is understood that each situation requiring repair is unique, agencies were asked if they had any standard or commonly used plans, specifications, procedures, or details for PT repairs or, specifically, for tendon replacement. These questions were included to identify an agencyâs attempt to formalize repairs, transfer lessons learned from one case to another, or stan- dardize its response. Only one state, Minnesota, has published standard procedures for remedial grouting. PTI has published recommendations on appropriate sheathing repair approaches for monostrand tendons in building construction. Similar guidance is not published for common repairs performed in the bridge industry. States reported experience with a variety of PT system repairs, inspection, and maintenance actions (see FigureÂ 17). A notable seven states (Florida, Louisiana, Minnesota, New York, Oregon, South Carolina, and Virginia) report having performed external unbonded tendon replacements (Virginia did not complete the survey, but did report external tendon repair on the Varina-Enon Bridge). Only Minnesota conducted an internal tendon replacement. Florida has investigated the feasi- bility of internal tendon repair with the Wonderwood Connector, and it is moving ahead with Vehicle Impact Deck Repair/ReplacementRelated to CorrosionDuring Construction N um be r o f S ta te s 0 5 10 15 20 17 10 9 1 Figure 16. PT repairs by cause.
Survey 35Â Â an alternate repair approach (involving drying of tendons and injection with corrosion inhibi- tors; see Wonderwood Connector case example, ChapterÂ 3). Crack injections of PT struc- tures have been performed by 17 states. The use of injected corrosion inhibitor is reported by eight states: California, Florida, Louisiana, North Carolina, Ohio, Oklahoma, South Carolina, and Texas. Most states report using proprietary corrosion inhibitors in these efforts. Fiber- reinforced polymer (FRP) wrapping of PT structures is reported by five states. Thirteen states have regrouted tendons, and six states have provided additional member strengthening to structures to address corrosion or impact damage. To identify potential causes for later repair, agencies were asked to comment on particular aspects of post-tensioned construction. The survey asked respondents to evaluate the following: 1. Had the agency encountered problematic construction details? (FigureÂ 18) 2. Had the agency encountered problematic construction techniques or methods? (FigureÂ 19) 3. Had the agency encountered problematic materials, in the context of PT construction? (FigureÂ 20) Of the 35 responding states, nearly half (17) report issues with problematic construction details. States were asked to identify problematic construction details with which they had Note: NDT = nondestructive technique. Number of States Figure 17. Types of maintenance, inspection, or repairs performed.
36 Repair and Maintenance of Post-Tensioned Concrete Bridges Number of States Figure 18. Problematic construction details. encountered issues (see FigureÂ 18). The most commonly reported problematic details included duct splicing details (eight respondents), anchorage pour-back details (seven respondents), and confinement reinforcement (seven respondents). Although not a specific detail, nor one unique to post-tensioned structures, congestion of rebar and other hardware (in this case, PT) was a frequent issue requiring careful consideration by the detailer, according to several of the surveyed states. Six states identified other concerns they had encountered during construction of their PT structures, including problems with large shear keys cracking during erection and conflicts with blisters and/or deviators, deck-level grout tubes, and nonmetal ducts (Oregon). In communica- tions with several agencies outside of the survey, several expressed issues past and current with deviator/blister geometries. Common issues ranged from incompatible alignments to exces- sively sharp corners at deviators, leading to kinking or damage to the tendon duct. The review of several case examples (see ChapterÂ 3) reveals that duct conflicts at diaphragms and deviator locations were a recurrent problem for years before modifications to connections and refine- ment of the standard practices improved these details. Still, geometry issues remain. However, a detailing shift instituted in Florida in 2014 may provide a solution for other agencies: the
Survey 37Â Â diabolo-shaped deviator type. The appeal of this detail is the gentle angle change at the entrance of the deviator void, which eases the transition of the duct profile at deviation locations. Respondents less frequently identified construction techniques and methodology as problem- atic (12 respondents), suggesting that recent efforts to educate personnel through certification may be proving beneficial as a way to improve the state-of-the-art construction of post- tensioned bridge structures. Of the 36 respondents choosing to comment, 12 answered âyesâ that a construction technique/methodology was a concern. Issues identified by those states (see FigureÂ 19) included grout filling procedures, air pressure test procedures, and vacuum test proceduresâall of which occur during the injection process. No attempt was made in the survey to develop a timeline for the identified problematic methods/ techniques. Some agencies are still encountering and repairing issues with structures built in the 1980s and 1990s, while others are still addressing tendons filled with the high-chloride- containing proprietary grout (which has since been removed from distribution). These agencies may have responded with such repairs in mind. Still, states report issues with ensuring a completely full tendon without voids, and with passing pressure/vacuum tests. One state stressed that it was âimportant to have personnel requirements in special provisions for vacuum grouting personnel to make sure staff performing this work are qualified and well experienced in vacuum grouting.â Number of States Figure 19. Problematic construction methods.
38 Repair and Maintenance of Post-Tensioned Concrete Bridges Four states identified having issues with the removal of deck-level vents and the placement of the permanent caps. In general, the details for these areas are nonspecific, with methodology left up to the contractor. Several states have reported issues with those details and with the methods used to seal off deck-level vents, elaborating that deck-level vents are often left sticking up unprotected at the deck level, where they can be easily damaged by personnel and moving equipment. Other expressed issues related to deck-level vents include difficulty removing the vents, difficulty placing the permanent cap, and issues with preparing the areas for the secondary pour backs. Other reported construction âmethodsâ include issues with cast-in-place joints and deck/ panel alignment. Fifteen of 36 respondents reported dissatisfaction with specific materials used in post- tensioning, with the primary material of concern being grout filler material (see FigureÂ 20). Materials most often identified as problematic included grout filler materials (11 states) and pour-back materials (nine states). Another five states identified issues with epoxy grout materials. The Oregon Department of Transportation reported dissatisfaction with nonmetal ducts but did not provide further explanation. No states report issues with flexible filler, but this is not surprising given its relatively recent introduction to the U.S. bridge industry. States reporting issues with grout filler material provided further comment suggesting that their response was informed by past issues, before the introduction of prebagged thixotropic grouts. Several states specifically called attention to previous problems with excessive bleed water and chloride contamination. States describing issues with pour-back materials further specified that these materials had low workability and issues with shrinkage cracking, in their experience. Number of States 0 2 4 6 8 10 12 Flexible filler material Other Elastomeric coatings Prestressing steel Epoxy grouts Pour-back materials Grout filler material 1 2 3 5 9 11 0 Figure 20. Problematic materials used in PT.
Survey 39Â Â Inspection and Maintenance Many states report performing nonroutine inspections of their PT structures (see FigureÂ 17), including invasive inspections (14) and nondestructive techniqueâaided inspections (17). Nondestructive testing methods have been used in inspections, or investigated via research for potential use in inspection, by many states (see FigureÂ 21). Most states (29) are relying on visual methods of inspection for their post-tensioned structures, although others have investigated other nondestructive test methods. Less commonly, electromagnetic wave propa- gation (i.e., infrared thermography, impulse radar, ground penetrating radar; 10 states) and mechanical wave/vibration methods (i.e., acoustic emission, impact echo, ultrasonic, hammer sounding; 11 states) have been reported as methods used for PT assessment. Four states (Florida, Oregon, Pennsylvania, and South Carolina) have used electrochemical methods (i.e., half-cell potential). Indiana, Massachusetts, and Pennsylvania report using or investigating radiation methods (i.e., X-ray diffraction, radiography). One state (North Carolina) has used direct measurement of tendon force. A handful of state DOTs have formally investigated various methods of nondestructive testing techniques for evaluation of PT structures, including Pennsylvania (Naito, Jones, and Hodgson 2010; Naito and Warncke 2008), Florida (Azizinamini and Gull 2012), and Kansas. Each of these statesâ departments of transportation have collaborated with local universities in formal efforts to research available nondestructive test methods. Figure 21. NDE methods for PT inspection. Number of States 0 5 10 15 20 25 30 Direct measurement of tendon force Radiation methods Electrochemical techniques Magnetic methods Electromagnetic wave propagation Mechanical wave propagation and vibration methods Visual methods 1 3 4 7 10 11 29