If you’re not including precast elements in project bids, it’s time to think about doing so. Purists who think the only “real” concrete comes pouring out of a truck or a pump are losing out to competitors who’ve learned to exploit the scheduling and quality-assurance advantages of precast. This is especially true when it comes to winning jobs for public owners such as transportation departments, which frequently reward reductions in traffic interference and shorter closures.
Why Mix and Match?
Cast-in-place concrete may be the more traditional construction approach, but combining it with precast elements expands options for the entire project team.
European designers and contractors use the term hybrid concrete construction (HCC) for a system that integrates cast-in-place and precast concrete. Britain’s Concrete Centre defines HCC as “the combination of precast and in-situ concrete to form a quick, robust, and safe form of construction that benefits from the advantages of both types of concrete construction.” The Federal Highway Administration (FHWA) doesn’t use the term “hybrid,” but encourages transportation departments to use structural precast bridge elements and systems (PBES) to minimize public inconvenience when building new bridges and rehabilitating or replacing existing bridges.
Combinations of precast and cast-in-place frequently are used to manage cost and schedule. One recent project demonstrating how effective the technique can be is the Port Authority of New York & New Jersey’s “Raise the Roadway” project on the Bayonne Bridge, where schedule was a key consideration. This iconic steel arch bridge was completed in 1931 to connect New Jersey and Staten Island over the Kill van Kull, one of the world’s busiest shipping channels. Constructing a new roadway above the existing bridge deck to provide an additional 64 feet of clearance had to be completed in time to accommodate arrival of a new generation of taller container ships.
The quickly approaching deadline led the contractor, a joint venture of Skanska Koch and Kiewit Infrastructure Co., to use predominantly precast segments for the new roadway. A big part of meeting the schedule was constructing a large number of precast elements beforehand. Although the project was mostly precast segments, cast-in-place concrete was used in the main deck span, foundations, and closure pours.
Another recent project, also in New York, involving a mix of precast and cast-in-place concrete was a significant upgrade on the Kosciusko Bridge connecting the boroughs of Queens and Brooklyn. The badly deteriorated 75-year-old steel structure required an increasing amount of maintenance. The Brooklyn and Queens approaches were rebuilt using low-maintenance precast girders and a mix of cast-in-place and precast decks.
Working Around Weather
Scheduling pressures of another sort led engineers to opt for various precast elements to replace the Champlain Bridge over the St. Lawrence River and Seaway in Montréal, Quebec, Canada. The region is extremely cold for six months of the year, so contractors working on the 42-month design-build project had only 21 months of viable construction time.

“We sat down with the contractor and asked ourselves how we could meet this very aggressive schedule,” says Marwan Nader, lead designer with T.Y. Lin International, managing partner in a joint venture with International Bridge Technologies and SNC-Lavalin. The answer was using cast-in-place concrete for a portion of the structure and precasting repetitive elements.
The main span is only 240 meters long, but long approaches on both sides of the river bring the total length to 3.4 kilometers. Infrastructure Canada, a department of the federal government, specified that pier spacing on the approaches could range from 60 meters to 80 meters.


“Although 60 meters works very well for concrete structures, making the span longer doesn't really help,” Nader says. “Steel-only could go to 80 meters or even 90 meters; but at that point you have to have an orthotropic deck, which would be a bit difficult to fabricate.” The team decided on a composite structure. “This allowed us to go with 84-meter spans, reducing the number of foundations by two piers.” Precast deck panels also avoided complex orthotropic deck fabrication.
All the piers and the tower up to the horizontal crosspiece were precast, which allowed the contractor to work day and night without worrying how temperature would affect the concrete. Precasting also kept foundation work on track despite the river’s strong currents. “The foundations are sitting on reasonably good rock,” Nader says. “We were able to precast the footings and lift them into place, basically just preparing the ground, then sinking them to the ground. With the top of the pier sticking out of the water, the contractor could bring those precast elements to it, allowing the work to be executed very quickly.”
Pier caps were also bid as precast. However, “we realized that, at 70 meters wide, each is for all practical purposes a bridge,” Nader says. “They were going to be very heavy to lift into place even divided into two pieces. So we did value engineering and, halfway through, decided to make them out of fabricated steel.” Thanks to the team’s creative approach, the new Champlain Bridge is on track to open by the end of 2018.
Not Just for Megaprojects
Hybrid construction works for smaller projects, too, often when transportation departments want to quickly replace multiple bridges. Lauded by FHWA as an excellent example of accelerated bridge construction (ABC), the Tennessee DOT’s “Fast Fix 8” replaced eight bridges in downtown Nashville in 10 weekends. Through careful and creative planning, the project team -- engineer Gresham, Smith and Partners; contractor Kiewit Infrastructure South Co.; and subcontractor Jones Bros. Contractors in addition to Tennessee DOT -- used four different techniques to replace four twin bridges. Two of the four incorporated precast elements.
On the Jo Johnston overpass, three-span structures were replaced with single-span bridges using prestressed box beams and full-depth deck panels. Precast end walls were installed on the existing bent caps, and the end spans were eliminated by using mechanically stabilized earth. Precast panels with conventional reinforcing were used for the approach slabs to further speed construction. The replacement bridges were built in two weekend closures.
Four spans were eliminated at the Clinton Street/CSX overpass. Precast elements form two spans of the new superstructure, which was put into place with similar speed and efficiency.
Performance Check
Precast bridge decks have been installed since 1965, but no one’s compared their performance to cast-in-place decks. David Garber, P.E., assistant professor in Florida International University’s Civil and Environmental Engineering Department and co-director of the U.S. DOT’s Accelerated Bridge Construction University Transportation Center, is overseeing a study designed to close this knowledge gap.
The website for “Performance Comparison of In-Service, Full-Depth Precast Concrete Deck Panels to Cast-in-Place Decks” cites a 2016 report from FHWA’s Long-Term Bridge Performance Program that describes investigators’ findings from examining a New Jersey bridge deck, one in a pilot study of seven bridges across the U.S. with similar superstructures and environmental conditions. Combined with findings from the other bridges, the pilot study is expected to validate test methods for future investigation and provide a baseline for ongoing performance assessments.