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Route 36 Highlands Bridge, New Jersey.
HPC for Route 36 Highlands Bridge, NJ
Chester Kolota, Federal Highway Administration
The Route 36 Highlands Bridge in Monmouth County, NJ, replaces the existing bridge, a 1240-ft (378-m) long, low-level, double-leaf bascule bridge that connects the boroughs of Highlands and Sea Bright. The bridge is part of an emergency evacuation route from the seashore towns to the mainland. The new mid-level fixed bridge over the Shrewsbury River consists of twin 65-ft (20-m) high segmental box girder structures that are approximately 1611 ft (491 m) long with a maximum span of 232 ft (71 m). The new bridge will eliminate many existing substandard features of the old bridge and remove the vehicular and marine traffic conflicts that existed with the movable bridge. Construction is scheduled to be completed by spring 2011.
Components of the Highlands Bridge were precast at three different plants: square piles at Precast Systems in Allentown, NJ; cylindrical piles at Bayshore Concrete Products in Cape Charles, VA; and segmental box girders and the pier columns at Unistress Inc. in Pittsfield, MA. Different concrete compressive strengths were specified for different components.
The use of high performance concrete (HPC) was critical for this project due to the bridge being located in a salt water environment as well as exposed to roadway deicing salts. In order to mitigate these environmental risks, the New Jersey Department of Transportation specified the following performance requirements for development of the HPC mix design:
2. Test specimens loaded at 28 days and under load for 180 days.
3. After 32 weeks of drying following 4 weeks of wet curing.
Acceptance requirements for the production HPC consisted of the following:
Concrete Mix Proportions
A Class P-5 concrete with the following mix proportions was used for the pier segments and the segmental box girders:
Segmental Match Casting using HPC
Production time for the precast pieces was critical when using HPC due to the low water-cementitious materials ratio combined with the high cementitious materials content. A Type F high-range water-reducing (HRWR) admixture was used in large quantities to improve workability. However, once the HRWR admixture began to dissipate, workability became more difficult for the finishers. The potential for the concrete setting before it could be finished was mitigated by the use of a roller screed that enabled the segment to be finished very quickly. Both the pier and the box girder segments used a single-sided match-cast system. Low pressure steam was used to cure the segments, but because they were match cast, each segment was steam cured twice. Following a pre-steaming period of 4 hours, the segments were steam cured for approximately 8 to 10 hours, which achieved the 2500 psi (17 MPa) strength required to remove formwork. The segment was then allowed to cool and moved to the match-casting bed, where it was positioned against the formwork for the next segment. After placing concrete for the next match-cast segment, the initial segment was steamed again for 8 to 10 hours until the new segment achieved the stripping strength.
A mix with fly ash can slow down strength development and production. However, the mixes used almost always made the required strength for post tensioning within 3 days, which allowed the contractor to transversely post-tension the segment and grout it quickly to keep ahead of schedule. Final 28- and 56-day concrete compressive strengths averaged between 8500 and 10,000 psi (59 and 69 MPa), well above the required strengths.
Further information about the Route 36 Bridge is available in ASPIRE, Summer 2010 and from the New Jersey Department of Transportation at http://www.state.nj.us/transportation/commuter/roads/route36highlands/.
HPC Bridge Views, Issue 66, Mar/Apr 2011