Innovative Bridge Designs for Rapid Renewal (2014)

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340 A p p e n d i x d introduction Phase III of SHRP 2 Renewal Project R04 required the con- struction of a demonstration bridge using the most-promising bridge details identified in earlier research and the modular systems being incorporated into accelerated bridge construc- tion (ABC) standards. The US-6 bridge, which crosses Keg Creek near Council Bluffs, Iowa, is similar in size and length to a large majority of bridges across the United States. As a demonstration, it was replaced with a bridge that incorpo- rates proven ABC bridge construction details with the inno- vative use of ultra-high-performance concrete (UHPC) to shorten the normal bridge replacement period from 6 months to only 2 weeks of traffic disruption. The improvements consist of replacing the bridge located on US-6 over Keg Creek in Pottawattamie County, Iowa. The existing 180-ft by 28-ft continuous concrete girder bridge (with spans of 81 ft, 48 ft, and 81 ft) was constructed in 1953 and was classified as structurally deficient with a sufficiency rating of 33. The replacement structure is a three-span (67 ft, 3 in.; 70 ft, 0 in.; and 67 ft, 3 in.) 210-ft, 2-in. by 47-ft, 2-in. composite steel modular bridge with precast substructures and pre- cast bridge approaches. The bridge replacement is intended to increase the structural capacity of the bridge, improve roadway conditions, and enhance safety by providing a wider roadway. This application provided a unique opportunity to effec- tively promote ABC for rapid renewal of the bridge infra- structure and also demonstrate various ABC technologies being advanced in the R04 project. The steel modular option was chosen as the most cost-effective on the basis of early discussions with local contractors and fabricators. Although it will not be fully detailed on the design plans, the contrac- tor was allowed to propose a precast concrete modular alter- native under a value engineering (VE) option if it can be constructed within the same ABC schedule and at a lower cost—none was proposed. The bridge was originally designed in-house to be constructed with a 13-mi detour (average daily traffic [ADT] = 7,000) and an estimated construction duration of 6 months. HNTB Corporation, a design engineering firm, redesigned the bridge by using ABC techniques and standard designs developed for this project so that the replacement could be completed in a 2-week period. The ABC period of 2 weeks pertains only to the time that traffic was disrupted. The total duration for the project, including time for prefab- rication, was about 7 months, but the traveling public was affected for only just over 2 weeks. A daylong workshop, including a site visit, provided an opportunity to promote the dissemination of information to bridge owners from around the country. The demonstration bridge features precast concrete semi- integral abutments, precast columns and pier caps connected with high-strength grouted couplers, and an innovative mod- ular superstructure constructed with prefabricated concrete decked, steel stringer units and field-cast UHPC joints. The enhanced durability provided by the elimination of all open deck joints is seen as a major advance in long-life ABC proj- ects; and the assembly of precast units without the need for any posttensioned connections avoids the need for specialized contractors. The project was the first in the United States to use ultra- high-performance concrete (UHPC) to provide a full, moment- resisting transverse joint at the piers. This detail allows the prefabricated superstructure elements to be erected as a sim- ple span and, once the UHPC joints are constructed, perform as continuous joints. The project team is performing full- scale laboratory testing of the critical field-cast UHPC conti- nuity joints to ensure their long-term reliability and ultimate load capacity. These UHPC joints provide simple construc- tion, additional load-carrying capacity, and a durable joint that prevents moisture intrusion and long-term maintenance problems. Field Demonstration Project Construction

341 demonstration project innovative Features This demonstration project implements a series of innova- tions. It incorporates details drawn from diverse locations and applies them in a single demonstration project that was visited by Federal Highway Administration and department of trans- portation personnel from numerous states. Project innova- tions include the following: • Overall, a complete bridge system was designed and con- structed by using superstructure and substructure systems comprising prefabricated elements. The bridge approach slab also consists of precast elements. • The superstructure units incorporate precast suspended backwall elements to create a semi-integral abutment. • Ultra-high-performance concrete was used in the joints between the modular superstructure units and between the approach slab panels. UHPC was used for longitudinal joints and transverse joints over the piers. This project was the first in the United States to use UHPC to provide a full, moment-resisting transverse joint at the piers. The elimi- nation of open deck joints provides for a more durable, low-maintenance structure in the final condition. • Self-consolidating concrete (SCC) was used to improve consolidation and increase the speed of construction for abutment piles (fill pockets) and abutment to wingwall connections. Abutments consist of prismatic, precast con- crete elements that feature a series of open holes to accom- modate driven steel H-piles. • Fully contained flooded backfill was used at the abutments. This proven construction method, ideally suited for ABC, involves placement of a granular wedge behind the abut- ment backwall, which is flooded to achieve early consolida- tion and significantly reduce the potential for formation of voids beneath the approach pavement. • A structural health monitoring system (HMS) plan was implemented to evaluate and document the innovative aspects of accelerated construction. The monitoring plan included health monitoring instrumentations to assess the integrity of the structure and deck panel system during and after construction. • ABC entails prefabricating as many of the bridge compo- nents as feasible given site and transportation constraints. This project took the approach that, for ABC to be success- ful, ABC designs should provide maximum opportunities for the general contractor to do its own precasting at a stag- ing area adjacent to the project site or in its yard with its own crews. The components were designed so that a local con- tractor could perform all or almost all the precasting work and outsource little to precasters. The winning bidder chose to do that by leasing a temporary casting yard next to the bridge site. • The technologies incorporated into this bridge project have been successfully used in constructed projects drawn from around the United States. Several diverse structural systems were assembled and incorporated into a single project, reinforcing the concept that innovation does not necessarily mean creating something completely new, but rather facilitating incremental improvements in a number of specific bridge details to fully leverage previously suc- cessful work. This demonstration project can affect the future practices of the industry and the state departments of transportation. New technologies that are implemented successfully on this project will accelerate the adoption of the innovations in the United States. This will be accomplished by creating aware- ness and education related to the innovative features and Figure D.1. Original Keg Creek bridge. Figure D.2. New Keg Creek bridge.

342 increasing confidence among government and other stake- holders in recommending their use on other projects. demonstration project Construction The US-6 bridge, a three-span continuous structure that crosses Keg Creek near Council Bluffs, Iowa, is similar in size and length to a large majority of bridges across the United States and was replaced as a demonstration bridge in Phase III. The Iowa DOT has significant experience in accelerated bridge construction, including projects on both the primary and secondary road system. A challenge in identifying this type of demonstration project is often presented when the project must be constructed in line with both the owner’s program schedule and the research team’s schedule to deliver a project. The research team identified a project that met both of these critical objectives. The following sections will present the construction pro- cess for the bridge: prebid meeting; contractor bids; site prep- aration and prefabrication; construction process for bridge, including work before the ABC period; and the postconstruc- tion review meeting. Prebid Meeting A prebid meeting was conducted on January 21, 2011, at the Iowa DOT central complex in Ames. A wide range of primar- ily Iowa-based contractors attended. All were interested in learning more about the project before submitting a construc- tion bid. Representatives from Iowa DOT and the SHRP 2 R04 project design team made detailed presentations on the inno- vative design aspects of the bridge and answered questions from potential bidders. A number of questions were raised about UHPC and the differences in how it is mixed and placed compared with con- ventional concrete. Another significant point of interest to the contractors was the potential need to adjust for differen- tial camber between adjacent superstructure modules. Significant attention was also paid to the three-phase proj- ect schedule that would be followed by the successful bidder. Essentially, the contract was separated into three phases: cer- tain work could be performed before the existing bridge was closed, some tasks could be performed only during the spec- ified 14-day ABC period, and the remaining tasks could be done after the bridge reopened. The Iowa DOT chose this three-phase schedule to keep the specific ABC research work separate from the non-ABC-related work items. During the 14-day ABC period, the contractor would be subject to liquidated damages at a rate of $22,000 per day. That amount was calculated on the basis of the user costs for the site given the measured traffic volume and 13-mi detour length required. Although the amount is much higher than the nominal amounts often used by bridge owners, the Iowa DOT believed that it was a measureable indicator of the importance of meeting the 14-day schedule. In summary, the work under this contract was organized as follows: • Stage 1: Before bridge closure 44 Construct drilled shafts to ground level. • Stage 2: ABC period (14 days) 44 Close bridge and demolish existing bridge. 44 Construct wingwalls on piles. 44 Assemble precast piers. 44 Assemble semi-integral abutments. 44 Assemble modular superstructure. 44 Assemble precast approach slabs. 44 Cast UHPC closure joints and grind deck. 44 Cast in place pavement, shoulder, and guardrail. 44 Reopen bridge to traffic—end of ABC period. • Stage 3: After bridge opening 44 Make channel improvements. 44 Construct reinforced-concrete flume. Contractor Bids The construction letting for the project was held on Febru- ary 15, 2011. Seven fully responsive bids were received on the Keg Creek bridge project, with a low bid of $2.66 million sub- mitted by Godbersen-Smith Construction of Ida Grove, Iowa. A summary of submitted bids follows: • $2,658,823.35, Godbersen-Smith Construction. • $3,202,409.35, A. M. Cohron Son Inc. • $3,245,342.21, Cramer and Associates, Inc. • $3,495,701.97, Hawkins Construction. • $3,614,301.52, United Contractors Inc. Subsidiaries. • $3,925,936.43, Jensen Construction Company. • $3,990,723.50, Kiewit Infrastructure Co. The bids included several additional items, such as stream sta- bilization and drainage improvements that were not actually part of the ABC project itself. Although the low bid slightly exceeded the Iowa DOT budget and the engineer’s estimate for the project, the owner agreed to proceed with the project knowing the critical importance of the project. Following the bid opening, the Iowa DOT performed an analysis of the bids to better understand how the costs for this ABC project differ from those of a conventional bridge. The Iowa DOT’s typical method for comparing bid prices excludes mobilization and bridge removal and results in an average cost of $175/ft2 of bridge area. However, because of the spe- cialized requirements for accelerated construction, these work

343 tasks were bid at a much higher price than for a typical bridge. When mobilization ($25/ft2) and bridge removal ($20/ft2) are included in the summary, the average bridge price is approxi- mately $220/ft.2 The higher bid prices for the ABC demonstration bridge can be greatly offset by a significant savings in user costs. In addi- tion, the 2-week construction duration greatly reduced the period of time that drivers and construction field personnel were subjected to additional risks. Likewise, since this bridge was constructed on a closed road, rather than on an on-site detour, the risk of potential public–worker collisions was elim- inated. The actual dollar cost savings for these types of risk reduction measures are difficult to quantify, but certainly pro- vide additional justification for future ABC projects. Site Preparation Because of a number of other ongoing projects and unantici- pated work generated by record flooding in the summer of 2011, the contractor did not begin substantial mobilization until July. The bulk of the mobilization work involved removal of a few small to moderate-size trees and grubbing the work areas. The contractor acquired a short-term lease on approxi- mately 4 acres of farmland immediately adjacent to the south- east corner of the bridge site. This land was used as an on-site fabrication and casting yard and was prepared with a number of 12-in.-thick timber crane mats, supported on a sand bed- ding to provide a uniform bearing surface and a level area to build forms and cast the bridge components. The close prox- imity of the casting yard was a tremendous benefit to the con- tractor’s operations and is a distinct advantage for bridges in a rural area where space is available. Preclosure Fabrication To prepare for the 14-day ABC period when the existing bridge would be demolished and replaced, the contractor performed a number of off-line operations that could be completed with- out affecting the traffic on US-6. Each of these operations will be briefly discussed in the following sections. Structural steel fabrication for the bridge was performed by DeLongs of Jefferson City, Missouri. During the shop drawing phase of the project, the contractor elected to construct the steel rolled beams without camber to simplify the fabrication. Although the dead-load deflection due to the deck concrete would cause a visible sag in the bottom flange, given the rural location of the project site, this was not seen as objectionable. The contractor assembled all of the structural steel on timber falsework in the assembly yard. The falsework was constructed to simulate the exact geometry of the permanent piers, includ- ing the same cap beam cross slope and elevation differences between piers and abutments. Figure D.3. Contractor mobilization and casting yard. Figure D.4. Aerial view of bridge site. Figure D.5. Timber falsework bents and steel beams.

344 Structural steel assembly was performed using bolted splice plates to connect adjacent modules at pier location. Although the spans were designed with sufficient moment capacity to function as simple spans, the transverse deck joints were also designed with sufficient capacity to provide continuity between adjacent spans with the impermeable UHPC bonded to the precast concrete to eliminate the intrusion of water into those joints. The bolted splices provide the compression flange connection at each location, and the UHPC joints in the deck provide the tension connection. The welded connection of the splice plates at each pier was modified during construc- tion to eliminate the need for fillet welds on both sides of the L-shaped connection plates. The double-sided filled weld was replaced with a partial-penetration weld that provides an equal capacity. Drilled Shaft Construction Drilled shaft construction was performed by Longfellow Drill- ing of Clearfield, Iowa. The drilled shafts were constructed just outside the footprint of the existing bridge, which allowed traffic to continue throughout. During construction of the shaft on the northwest corner of the bridge, the drilling operator observed the remnants of a timber pile as it was brought up from the bottom of the shaft. An investigation could not determine whether this pile was part of the existing bridge foundation, part of a previous bridge, or even a falsework pile. As a precaution, the Iowa DOT closed the westbound lane of the bridge for a few days while the drilled shaft concrete was placed to avoid any poten- tial vibrations to the early-age shaft concrete. Reinforcing cages for the drilled shafts were fully tied in the assembly area and moved down to the pier locations for inser- tion and concrete placement. To accommodate the grouted coupler connections to the precast column sections, a set of #14 reinforcing bar dowels were embedded in the top of the drilled shaft concrete before initial set. It was absolutely criti- cal that these dowels be accurately set to match the columns, so the contractor constructed laser-cut templates for both halves of the connection. The dowels were placed in the cor- rect orientation and elevation and secured in place until the shaft concrete was cured. Deck Construction and Concrete Casting The contractor elected to cast the entire deck as one continu- ous concrete placement rather than a series of individual Figure D.6. Steel superstructure on falsework bents. Figure D.7. Drilled shaft construction adjacent to existing bridge. Figure D.8. Installation of dowel bars for drilled shaft.

345 superstructure modules, as might be considered in a typical precast concrete plant. To create space for the joints between each module and permit separation of the pieces and future reassembly, the contractor constructed a grid of plywood blockouts that would allow the installation of the overlapping hairpin reinforcing but would also be easy to disassemble after the concrete was cured. Before placement of the bridge deck concrete, researchers from Iowa State University installed a series of strain gauges, attached to the reinforcing steel at several locations near the west pier. The gauges were used not only during load testing before the bridge was opened but also as part of a health mon- itoring system that will be used to document in-service bridge performance (this instrumentation is not part of SHRP 2 Project R04). The bridge deck concrete was placed very much like any other bridge deck by using a full-width Gomaco finishing machine. Concrete placement was started at one end of the deck and proceeded continuously to the opposite end of the deck without any significant incidents or delays. Although this construction method required quite a bit of handwork to finish the concrete around each of the plywood blockouts, it allowed the contractor to construct a new type of modular bridge and to do it with tools and equipment with which the crew was very familiar. Curing of the bridge deck was per- formed per Iowa DOT standards with a 7-day wet cure that used burlap, soaker hoses, and thermal blankets. Substructure Components Pier columns were constructed vertically on a forming bed consisting of 12-in.-thick timber crane mats. The forms were guyed and braced before concrete placement and remained so until the columns were moved to their permanent loca- tion. Lifting and guying of pier columns was performed by using strands embedded in the top center of each column and threaded inserts in the top of each face. To accurately place the grouted reinforcing couplers before pouring concrete, the contractor built laser-cut templates to match similar tem- plates in the drilled shafts and cap beams. Abutment and wingwall components were also cast on a forming bed consisting of 12-in.-thick timber crane mats. To ensure fit-up of the abutment and superstructure pieces Figure D.9. Deck concrete placement using finish machine. Figure D.10. Deck reinforcement and plywood blockouts. Figure D.11. Pier columns formed in casting yard.

346 during the ABC period, the precasting work had to be accu- rately measured and verified before placing concrete. Pier cap beams were formed and placed on temporary cast- ing beds located beneath and immediately adjacent to the existing bridge on a temporary creek crossing. Given the heavy weight of the caps, approximately 168,000 lb each, the loca- tion was selected to reduce the distance that the cap beams would be moved after curing. The contractor elected to use cast anchor bolts for bearing devices into the concrete rather than drilling/grouting or using anchor bolt wells. Posttensioning Retrofit Design and Testing Laboratory testing of the full-scale bridge superstructure modules was performed at Iowa State University before con- struction commenced. The results of those lab tests are pre- sented in Appendix C of this report. Those test results showed that the bond between the UHPC joints and the precast deck concrete was not adequate to prevent the debonding of the two materials under tension loads. The modules were designed to allow them to perform as a simple span without the need for a supplemental connection between spans. However, to prevent intrusion of moisture into the deck, it was greatly preferable that the joints remain closed during service loads. The R04 team developed a simple, posttensioned retrofit that could be installed after the modules were installed and the UHPC was cast. This retrofit included simple brackets mounted to the top of the beam webs, a 1-in.-diameter 150-ksi threaded rod, and anchorage hardware. Initially, the posttensioning force at each rod was specified at 60 kips per rod. This force level was selected because, according to the manufacturer, a contractor could apply that level of force simply by applying the required torque on the anchor nuts with a torque wrench and multiplier. Following subsequent load testing at Iowa State University, the level of posttensioning was increased to 70 kips per rod to ensure that the deck joints remained fully compressed during service loads. In addition to the posttensioning retrofit, the team decided to provide an epoxy bond between the UHPC and precast deck concrete. Although this retrofit could not be tested in the laboratory because of time constraints, the additional bond between UHPC and precast concrete was critical to the long-term success of the project. In the actual Keg Creek bridge, this bond was provided through the use of Rezi-Weld adhesive applied to faces of the transverse deck joints imme- diately before placement of UHPC. Fourteen-Day ABC Period As part of the normal project submittals, the contractor was required to submit a detailed schedule of operations to be conducted during the ABC period. The Iowa DOT and the SHRP 2 team carefully reviewed this schedule to ensure that the contractor would have sufficient equipment and man- power available to complete the work on time. Figure D.12. Pier cap beam casting adjacent to existing bridge. Figure D.13. Posttensioned retrofit for modules. Figure D.14. Epoxy adhesive being applied to joint faces.

347 Contractor working hours during the ABC period were typically from 6:30 a.m. until 8:00 p.m. unless critical oper- ations had to be completed to maintain the schedule. The contractor was careful to ensure that all operations requiring especially precise work, such as lifting and placement of large bridge components, were completed during daylight hours. These working hours, especially on a 7-days-per-week sched- ule, were challenging for the on-site workers. Because of the shorter daylight hours during the fall season, the productive working hours were somewhat less than what would be avail- able during June or July. With longer working days, or even using a split shift for workers to staff the project nearly round- the-clock, the work required to replace a similar bridge could potentially be completed in a shorter closure period. The contractor did not use any unusually large or special- ized equipment for the demonstration project. At times, as many as seven cranes were working on the site. Most cranes were of moderate size, typically 110-ton capacity. During the erection of the large abutment and superstructure module components, a large 200-ton hydraulic crane was used. Two other types of equipment proved invaluable during the ABC period: hydraulic boom lifts and portable lighting units. The contractor commonly used as many as six boom lifts at any one time and often had up to 10 lighting generators available to permit safe working conditions during all hours of the day or night. Demolition of Existing Bridge The existing bridge was removed within a single day by using two hydraulic breakers mounted on tracked excavators and an American 7250 crane with wrecking ball. During demoli- tion, the precast pier cap beams were protected from falling debris with additional timber crane mats. Concrete from the existing bridge was cleaned of reinforcing steel and crushed for use as channel protection material on site. The salvaged reinforcing steel was removed and recycled at an off-site facility. Abutment Construction Abutment construction consisted of a series of relatively sim- ple and conventional operations: • Excavate and create earthwork bench for piles. • Drive steel H-piles to the appropriate bearing capacity at locations matching pocket voids. • Cut off piles to the final elevation—2 ft above the top of bench elevation. • Attach welded studs to the tops of the piles. Figure D.15. CPM schedule during ABC period. Figure D.16. Demolition of existing bridge deck.

348 • Transport two abutment barrels and four wingwall units from the casting yard to the bridge site. • Lift and place precast abutment barrel and wingwall sec- tions over the protruding steel H-piles. • Place SCC in annular spaces around steel H-piles and between the joints connecting the abutment wing walls to the abutment footing. Pile driving presented no particular problem for the con- tractor. To save time, abutment piles were simultaneously driven at both abutments. The contractor elected to provide an additional 10 ft of steel piling at each plan location to avoid potential delays during the ABC period (this stipulation may be provided in the contract to avoid delays). Ultimately, the piles reached the desired bearing capacity very near the antici- pated elevation, but the minimal amount of waste was deemed “cheap insurance” against potential problems. The contractor requested and was given approval to change from the steel shear studs welded to the upper section of the piles to a drilled-through, high-strength threaded rod at each location. This change was made to speed the construction and eliminate the need for an automatic stud welder on site. Movement of the abutment components from the prefab- rication yard to the bridge site required the use of a six-wheel- drive straight truck and a pair of moderate-size bulldozers to provide additional traction on the steep grade over the tem- porary creek crossing. This crossing was not designed by the project team and was installed by the contractor as part of the site preparation work. Each abutment consists of a barrel section and two wing- wall sections that are combined to form a U-shaped configu- ration. Installation of these components was slightly complicated by the need to place all three sections at the same time while aligning the corrugated metal pipe (CMP) pile pockets with the driven piles in each section. Overlapping hairpin reinforcing in the joints connecting these sections would not permit installation of one component at a time. This construction sequence did not present a major hurdle at the demonstration project site; however, the contractor observed that future projects in a more congested area might face a greater challenge if limited access was available to posi- tion cranes near the abutment. One significant problem occurred during the pile driving at the west abutment. Following installation of the abutment pieces, but before placement of the SCC in the pile pockets, the abutment was found to be approximately 26 in. east of the correct location. A survey error had led to the mistaken pile installation. After study and consultation with designer and owner, Godbersen-Smith decided to cut off and abandon the original set of piles and drive a new set in the correct location. This error and the resulting rework cost the contractor an estimated 2 days on the critical path schedule. Placement of the SCC presented no particular problems for the contractor. To support the abutment sections at the correct elevation while the SCC gained strength, the contrac- tor placed a series of 3-ft by 4-ft unreinforced concrete pads beneath the abutment barrel and wingwall sections. Before the contractor moved forward with the deck placement, the SCC compressive strength was verified by compression cylin- der tests after being cured in accordance with the Iowa DOT SCC material specifications. Pier Construction Before the ABC period, the drilled shaft foundations were constructed adjacent to the existing bridge. After the existing bridge was demolished, pier construction consisted of the following operations: • Cut off temporary casing at top of drilled shaft. • Prepare top of shaft concrete. • Move four column sections from casting yard to bridge site. Figure D.17. Abutment components moving to bridge site. Figure D.18. Installation of abutment and wingwalls.

349 • Place grout bed at top of drilled shaft. • Install precast column on top of drilled shaft, and install guy wires. • Place grout in reinforcing steel couplers at bottom of col- umn, and allow it to cure. • Move two cap beam sections into position for lifting onto columns. • Place grout bed at top of precast columns. • Lift cap beam sections, and set atop precast columns. • Place grout in reinforcing steel couplers at top of column, and allow to cure. Rather than attempt to lift and carry the precast column sections from the casting yard to the bridge, the contractor constructed a temporary bench approximately halfway down the slope from the yard. A simple three-step process was used to move the columns to the bridge: a crane working from the upper yard lifted the column and placed it on the bench, the column was temporarily guyed, and a crane from the lower area lifted the column from the bench and moved it to the bridge site. The tops of the drilled shafts were prepared by grinding away any roughness in the top surface of the shaft and using a hand-held band saw to cut the reinforcing dowels to the correct final length. A bed, ½ in. to ¾ in. thick, consisting of nonshrink W. R. Meadows 588-10k grout was constructed on top of the drilled shaft in preparation for setting the precast column. The grout bed was designed to completely fill any irregularities between the mating components; any excess grout would be squeezed out when the column was placed. Precast columns were placed by aligning the female end of the grout couplers with the dowel bars projecting from the drilled shaft. Once the column position was confirmed (by using survey) and verified (by using a cloth tape measure), a ½-in.-diameter guy wire was installed near the top of each Figure D.19. Movement of precast columns. Figure D.20. Reinforcing couplers before concrete placement. Figure D.21. Couplers in the bottom of precast column. Figure D.22. Placing precast column on drilled shaft.

350 face of the column and anchored to an immovable object to maintain column position. The grouted couplers at the bottom of the column were injected with Dayton-Superior S-L grout in accordance with the manufacturer’s specifications: Grout is injected with a hand pump through the port near the bottom of each coupler. Injection is continued until a steady stream of grout is observed oozing from the upper port of the same coupler. The ports are capped with a plastic plug, and the grout is allowed to cure approximately 18 hr until the required strength is obtained. Before the contractor moved forward with the superstructure module installation, the grout strength was verified by testing site-cured cube specimens in accordance with the manufac- turer’s recommendations. The heaviest precast components in the bridge were the pier cap beams. These pieces weighed approximately 168,000 lb and required two 110-ton cranes positioned on the temporary creek channel crossing to safely lift them into position. To help reduce the weight of these large pieces, two voided blockouts were created within the interior of the cap beam concrete by filling this volume with hollow plywood boxes. When the forms for the west pier cap beam were stripped, an unconsolidated area of concrete was observed near one of these plywood boxes. The owner expressed concern that this could indicate a potential shift in position by the plywood boxes. A series of ¾-in.-diameter test holes were drilled in the top and side faces of the cap beam to confirm that the boxes were in the correct position and no additional corrective action was required. A grout bed similar to that used at the top of the drilled shaft was constructed on top of each column. In addition, a 4-in.-wide strip of compressible foam rubber was placed around the perimeter of each column before the grout bed was placed. This rubber served to confine the grout and allow only excess to squeeze out when the cap beam was placed. The cap beams were lifted and placed with very little diffi- culty thanks to the accuracy of the templates used during the casting process. Following confirmation of the cap geometry, the couplers at the top of the column were grouted by using the same injection process as described earlier. This grout was again allowed to cure for approximately 18 hr before the first superstructure module was set. Superstructure Module Assembly Movement of the superstructure modules from the casting yard to the bridge site presented a number of challenges because of the large size and weight of the panels. In addition, the eccentric load caused by the integral barrier rail on the exterior modules, along with the 90° left turn and steep slope on the road to the bridge site further complicated the opera- tion. The contractor was very careful to block and strap the modules to the truck bed to avoid any tipping and to position Figure D.24. Pier column grout bed and dowels. Figure D.25. Installation of pier cap beam. Figure D.23. Injecting grout into reinforcing steel couplers.

351 the panel on the truck to maintain the center of gravity of the load between the wheel lines. Two cranes performed the lifting of the modules. For the end spans, a 200-ton truck crane was positioned behind the abutment and a 110-ton crane was positioned on the chan- nel crossing near the pier. For the center-span modules, two 110-ton cranes were positioned side by side near each pier, and the cranes “walked” forward to place the module in its final location. The fit-up of modules at each abutment presented a bit of challenge. Although the pieces were originally fit together in the casting yard, after being moved to the final location, a few reinforcing bars needed adjustment when the modules were set. The contractor used a handheld rebar bender to adjust bars as necessary. The final module at each abutment had to be lifted so that it hung perfectly plumb from the cranes to better fit into the opening between the wingwalls. In addition, the liberal use of liquid dish soap provided much needed lubrication to allow the final module to slide past the wing- wall and into position. The use of overlapping hairpin bars provides a very strong joint between modules but does complicate the construction somewhat because of tight tolerances for installation. Future applications of this bridge should evaluate other options (such as straight bars) that might simplify construction. The installation of adjacent modules with overlapping hairpin bars created what the contractor called a “piano hinge” for assembly. Following installation of the final module, straight reinforcing steel bars were slipped through the hairpins in each joint. The reinforcing steel in the joints between adjacent mod- ules was an ongoing point of discussion during the construc- tion phase of the project. For this project, the contractor elected to cast the modules on site in one large operation and thus had the opportunity to make slight adjustments in the placement of reinforcing steel to avoid conflicts between modules. In future applications, where modules might be cast individually, project designers should provide accurate tem- plates and evaluate potential details to reduce the number of reinforcing bars in these joints. Mixing, Transportation, and Placement of UHPC UHPC mixing was performed by a pair of ½-m3-capacity electric mixers positioned at the east end of the bridge. The Figure D.26. Movement of superstructure module. Figure D.27. Overhanging backwall at semi-integral abutment. Figure D.28. Assembly of modules creates “piano hinge.”

352 component materials for each batch were provided in bulk packages: an 1,800-lb “super sack” of powder mix and three boxes of steel fibers. In addition to the dry ingredients, water and the required admixtures were carefully weighed with a digital scale. UHPC was transported to the bridge by using several mobile “Georgia buggies.” The contractor fabricated plywood hoppers to minimize spillage and waste. UHPC was placed in the joints and allowed to flow around the reinforcing steel and completely fill the joint. The contractor used strips of ¾-in. plywood on each side of the joint to allow a slight overfilling. Once the concrete was cured, the excess concrete was ground flush by the diamond milling machine in the same operation as the profile and smoothness grinding. This grind- ing was performed within 48 hours of casting the UHPC to maintain the ABC schedule and to ensure that the UHPC had not gained full design strength at the time of grinding. Because of the very flat, but still measurable, crest vertical curve on the bridge, UHPC placement was started at each end of the bridge and moved toward the center (“working uphill”). To control the flow of UHPC during placement, each longi- tudinal joint in the end span was filled simultaneously until the pier was reached. Just uphill from the transverse pier joints, a series of removable acrylic bulkheads were installed in the longitudinal joints to ensure that the entire end span and the transverse joint at the pier were completely filled before mov- ing on to filling the longitudinal joints in the center span. Because of the relatively slow mixing and transportation pro- cess for the site-mixed UHPC, the placement of UHPC in the longitudinal joints was not completely efficient, and the contractor struggled at times to maintain a consistent level of UHPC in these joints. Future projects should consider filling only one or two longitudinal joints at a time and using bulk- heads or other means to control the flow of UHPC until the joints were completely filled. The ambient temperature at the time of UHPC placement varied from 40°F to 50°F. During the overnight hours follow- ing placement, the temperature dropped into the low 30s. To accelerate the curing process, the contractor used flexible ground heaters and insulating blankets to maintain the tem- perature in each joint at approximately 85°F to 90°F. Iowa State University performed laboratory testing of UHPC specimens after casting. Results of that testing are presented in Appendix C. The test results were immediately Figure D.29. Adding steel fibers to UHPC mixing process. Figure D.30. Mixing UHPC with super sack ingredients. Figure D.31. Placing UHPC in deck joints using Georgia buggy.

353 communicated to the contractor so that grinding of the deck concrete could be performed within the ABC schedule. Posttensioning of Superstructure Modules Installation of posttensioning rods was performed while the UHPC was curing, and stressing was completed after the UHPC had reached a minimum 14,000-psi compressive strength as verified by Iowa State University with specimen testing. The 1-in.-diameter 150-ksi rods were inserted through each pair of brackets (a total of 48 locations) and stressed to a force of 70 kips. The stressing sequence followed was one in which all four rods within a given module were stressed simultaneously to minimize any potential for eccentric loads that would crack the still-curing UHPC. Field-Welded Connections at Piers Because of the survey errors noted previously, the bridge essentially was constructed with a very slight horizontal kink at each pier where the abutments are approximately 4 in. south of the correct alignment. The design plans showed the use of an anchor bolt well at each pier to provide some con- struction tolerance for setting of the swedged anchor bolts; however, the contractor elected to cast the anchor bolts into the pier cap beam concrete. Given the lack of tolerance com- bined with the kinked alignment, the contractor was unable to complete the bolted flange splices at several of the girder loca- tions at each pier. Web splices were fully bolted and tensioned per the Iowa DOT standard specifications. At locations where the bolted splice could not be com- pleted, the contractor requested and received approval to substitute a fillet-welded connection at the piers. Although not the ideal solution, the field welding provided the neces- sary strength to ensure the compression component of the continuous girder spans at each pier as well as sealing each of the splice locations against future moisture intrusion. Precast Approach Pavement Construction Following installation of the final superstructure module, the next step was to construct the precast approach pavement at each end of the bridge. The precast approach pavement con- sisted of four doubly reinforced concrete panels, each 20 ft long and 10 ft, 7½ in. wide. Before installing the panels themselves, a floodable backfill system was installed behind each abutment. That consisted of a geotextile fabric liner to separate the bridge embankment from the porous backfill material, a perforated subdrain run- ning the length of the abutment and wrapping around each wingwall, and a porous backfill poured in layers approxi- mately 1 ft thick. As each layer of porous backfill was placed, it was flooded with water and subjected to vibratory com- paction. This method has been quite successful in eliminating approach settlement. A precast reinforced-concrete sleeper slab was installed and leveled using a bed of fine sand. The sleeper was cast with an integral 2-in. crown, matching the bridge deck and the approach roadway. The precast approach panels were installed and leveled to fill the space between the abutment wingwalls. This task was made more difficult and time-consuming by the contractor’s decision to place the approach pavement panel concrete on a prepared—but not completely smooth— subgrade in the casting yard. This caused the bottom sur- face of the approach panels to be somewhat rougher than anticipated. Although the plans called for the joints between the approach pavement panels to be filled with UHPC, the con- tractor requested, and was granted, a substitution to use SCC instead. The change was requested because the supply of UHPC component materials on site was low after overruns Figure D.32. Pier joint detail with posttensioning. Figure D.33. Installation of precast approach.

354 during the installation of the superstructure. The approach pavement joints and the lifting pockets in the superstructure modules were filled with SCC in a straightforward operation. By the following day, the SCC mixture, which contained Type III portland cement for rapid strength gain, had allowed enough shrinkage in the lifting pockets to permit the intru- sion of water around the perimeter. This seepage was later repaired with an epoxy injection. Following completion of the approach panels, the contrac- tor placed reinforced-concrete shoulder panels and an asphalt leveling course to precisely match the existing roadway pave- ment. In hindsight, the use of precast approach panels in this application may have been less than ideal. Given the need to construct a cast-in-place tie-in section anyway, a simpler solution might have been to place the entire approach as a cast-in-place area by using an accelerated curing process. Deck Grinding for Profile and Smoothness One of the final steps before opening the bridge to traffic was to grind the entire deck surface with a diamond grinder. The grinding had three purposes: to remove any irregularities on the deck surface especially at the UHPC joints, to correct any discrepancy in the longitudinal profile, and to provide increased skid resistance. Although the UHPC material is a much higher strength than conventional concrete and contains an infinite number of high-strength steel fibers, it did not appear to present any significant challenge in the grinding process. Following the grinding operation, the smoothness of the deck was mea- sured with a profilometer. Final results of that test are not yet available, but the bridge deck and approaches appear to pro- vide a smooth, quiet ride, and the transitions from approach pavement to bridge are quite good as well. Following the bridge grinding, in the UHPC concrete placed in the deck joints, in at least one area, the steel fibers were not uniformly mixed with the reactive powder components. The largest observed “fiber ball” was approximately 1.0 in. to 1.5 in. in diameter. Although this location might permit the intrusion of water beneath the surface of the UHPC joint, the low perme- ability of the material should prevent substantial seepage of water into the deck. Load Testing by Iowa State University Before opening the bridge to traffic, researchers from Iowa State University performed a live-load test on the bridge for the Iowa DOT to document the as-built performance of the structure (this work is not part of SHRP 2 Project R04). Highways for LiFe Workshop To more widely disseminate information about the construc- tion process and lessons learned from the Keg Creek bridge demonstration project, a national Highways for LIFE show- case was held in Council Bluffs, Iowa, on October 28, 2011. The showcase was held at the Hilton Garden Inn in Council Bluffs, a site that provided convenient access to the Omaha airport, the Interstate highway system, and the project site— which was approximately 15 miles away. Nearly 80 people from 14 states attended the showcase. The participants represented state DOTs, FHWA, designers, and contractors—all of whom shared an interest in accelerated bridge construction. Planning Planning for the showcase began in July and included a series of conference calls and online meetings to develop an agenda, suggest and confirm speakers, and organize the logistics for a meeting location and food service. The planning committee included representatives from the following: • National Academy of Sciences (SHRP 2); • SHRP 2 R04 project team; • Iowa DOT (Bridge Office and District 4); • FHWA (Iowa, Washington, and Atlanta); and • University of Florida. The University of Florida, working under a support contract with FHWA, produced the invitations and managed the reg- istration process. The showcase schedule had to remain somewhat flexible until only 3 weeks before the event. Because of the contractor’s activities and potential weather delays, the start date for the critical 14-day ABC period was not finalized until that point. Given the long distances travelled by many of the attendees, the planning committee wanted to ensure that the bridge con- struction would have reached an “interesting” phase on the day of the showcase.Figure D.34. Fiber ball on surface of UHPC joint.

355 Travel Funding A limited number of travel scholarships were provided by the SHRP 2 program to encourage participation from state DOTs across the United States. A number of bridge owners were given financial support for travel expenses for the showcase. Agenda The showcase agenda included presentations from a variety of viewpoints, providing an overview of the Highways for LIFE program, both national and Iowa perspectives on accel- erated bridge construction, and a detailed presentation on the design and construction of the Keg Creek bridge. Fol- lowing the event, the speaker presentations were made avail- able in PDF format for all participants. The presentations are also available for download on the Highways for LIFE website. Site Visit Following lunch at the conference hotel, showcase attendees were encouraged to visit the project site during the afternoon. Bus transportation was provided to the project site, and attendees were allowed to freely observe all aspects of the construction progress. Weather was cool and windy with temperatures in the low 50s in the afternoon. On the day of the showcase, the contractor was placing the UHPC material for all of the superstructure deck joints, which was an ideal time for the attendees to arrive. Visitors were able to observe the mixing, transporting, placing, fin- ishing, and curing operations. For most of the showcase attendees, this was their first in-person exposure to UHPC. During the site visit, countless small group meetings were held to share ideas and recommendations for future projects that might use some or all of the technologies observed. Evaluation Showcase attendees were asked to complete a brief evalua- tion to allow the organizers to assess the quality and useful- ness of the showcase content, as well as the potential for applying ABC technologies on upcoming projects in their own jurisdictions. Overall, the showcase event received very good reviews from the participants, with an average rating of 4.1 on a scale of 1 (poor) to 5 (excellent). Several participants provided con- tact information and agreed to participate in follow-up com- munications 6 months after the showcase to document how their future ABC projects are advancing. Project Website Given the significant national interest in the Keg Creek bridge project, the Iowa DOT established a project website (http:// www.iowadot.gov/us6kegcreek/) to provide access to a variety of project-related materials. These include the following: • Photo gallery; • Video gallery with time-lapse video of entire ABC period and project animations; • Detour information; • Plan drawings and technical details; and • Links to FHWA and Highways for LIFE websites. SHRP 2 Project R04 Video Documentary The SHRP 2 research team is currently producing a set of documentary videos under some additional funding from the SHRP 2 Program. Two videos will result—an approxi- mately 10-min version intended for an upper-level adminis- trator at a DOT that might be considering an ABC project, Figure D.35. ABC showcase in Council Bluffs, Iowa. Figure D.36. ABC showcase visit to Keg Creek bridge site.

356 and a longer version, approximately 25 min, geared toward a more technical viewer such as a DOT bridge designer, consul- tant, or contractor. The videos will be made available online through a variety of sources, including SHRP 2 and FHWA websites. postconstruction Review Meeting The Iowa DOT hosted a postconstruction review meeting in Ames on November 17, 2011. In attendance were representa- tives from the following: • Iowa DOT (Bridge Office, District 4, and Council Bluffs Residency); • SHRP 2 Project R04 research team (HNTB and Iowa State University); • SHRP 2 program manager; • FHWA (Iowa division); • Applied Research Associates (documenting project for SHRP 2); and • Godbersen-Smith Construction. The purpose of the meeting was to review the design and construction process for the demonstration bridge and to document not only the successful elements of the project but also those aspects that could be improved for future projects. The SHRP 2 Project R04 research team has developed stan- dard bridge details for this type of modular bridge, and many suggestions have been incorporated into those standards. A summary of lessons learned from this demonstration project is provided in the next section. Summary and Lessons Learned Overall, the Keg Creek bridge project was a tremendous suc- cess. The bridge was completely replaced in 16 days by using only conventional equipment and labor and without signifi- cant problems. All parties (owner, designer, and contractor) worked closely together to resolve challenges as they arose during the ABC period. A SHRP 2 Project R04 representative was on site during the ABC period to make immediate deci- sions when questions arose. This was a critical component to the overall success. Following the postconstruction review meeting, a summary of lessons learned was compiled: • On-site prefabrication of bridge components can be per- formed by contractors and result in a high-quality prod- uct. On-site inspection staff should be prepared for work that is not exactly like their normal projects. • On-site mixing and placement of trial batches of UHPC should be considered to help eliminate fiber balling issues. Early and proactive communication with the UHPC provider is critical to the success of the on-site placement operations. • Project special provisions should be carefully written to provide for both on-site and more-traditional precast con- crete operations. The special provisions should describe casting, quality assurance, and inspection. • The bond between UHPC and conventional precast con- crete is critical. Surface preparation before placement of UHPC should be performed according to the manufac- turer’s recommendations. Future direct tension testing of bond specimens at Iowa State University will be beneficial in understanding this condition. • Field placement of UHPC in large quantities can be challeng- ing to manage. For future projects, cold joint bulkheads should be strategically placed to manage UHPC pours effi- ciently. Separating the UHPC pour in the suspended back- wall from the slab joint pour might also be beneficial. • Joint reinforcement that uses hairpin bars should be care- fully evaluated for future projects. Simplifying the joint con- struction with reinforcement details that allow the joints to be more easily constructed may be possible. Bars should be staggered and projecting bars shortened if possible. • Joint reinforcement congestion should be carefully evalu- ated for future projects. Reducing the number of longitudi- nal bars to allow these joints to be more easily constructed may be possible. Bars crossing at the joint intersections cre- ate congestion and time-consuming placement methods. • Surveying is a critical element of fast-track bridge replace- ment projects. To avoid critical and time-consuming errors, two sets of independent surveys should be used to verify accurate pile driving and foundation placement during the ABC period. • Precast approach pavement may not be the most efficient means of connecting an ABC bridge to the adjacent road- way. Placing a section of cast-in-place approach concrete by using accelerators may be faster since a small closure pour will almost inevitably be needed in any case. • Additional isometric views should be included in plans to allow contractor and inspection personnel to better under- stand how the bridge components fit together. • Although no backup plan was needed on this project, the contractor should have one in the event that a bridge com- ponent is damaged during the ABC period. At the very least, a repair plan should be agreed upon in advance. • Ideally, the designer should be present on site during the ABC period to facilitate quick decision making. On the basis of the lessons learned from the Keg Creek dem- onstration bridge project, several adjustments were incorpo- rated into the proposed ABC standards presented elsewhere in this report. These adjustments were intended to improve con- structability and reliability and to provide improved opportu- nities for future plant-cast and site-cast ABC projects.