Byron F Velasquez, Greg Nault
The Delaware Memorial Bridge is a twin span suspension bridge crossing the Delaware River between New Castle, Delaware and Pennsville, New Jersey. The bridge is named in memory of the soldiers from Delaware and New Jersey who died in World War II, the Korean War, and the Vietnam War. The first span (now NJ-bound bridge) was built between 1949 and 1951 and the second span (now DE-bound bridge) was built between 1964 and 1968.
Each bridge has a total length of 13,500 feet (4,115 meters) with a main span length of 2,150 feet (655 meters). The towers and roadway stand 440 feet (134 meters) and 175 feet (53 meters), respectively, above the water to allow for large ships to pass underneath. These bridges serve as a major transportation route between the Northeastern United States and the southern states, with more than 100,000 vehicle crossings daily. It is owned by the Delaware River and Bay Authority (DRBA), which is responsible for its operation, maintenance, and repair funded largely through toll revenue.
A bridge deck study conducted on the New Jersey bound bridge determined that the existing concrete deck was starting to exhibit accelerated deterioration and required substantial repair. WSP, consulting engineers, proposed a partial-depth deck reconstruction using Ultra High-Performance Concrete (UHPC) as the most effective solution due to its cost-effectiveness and long-term durability. Alternatively, a full-depth deck replacement would have been significantly more expensive, taken longer to construct, and been much more disruptive to traffic.
In 2020, a pilot installation was completed in which a UHPC overlay was installed on three different sections of the bridge and then subsequently monitored. In Fall 2022, Phase 1 of the full bridge work commenced. The reconstruction includes the removal of the top 2-in. (50-mm) of existing concrete bridge deck via hydrodemolition and then replacement with a similar thickness of an Ultra High-Performance Concrete (UHPC) overlay.
At the conclusion of this project in Fall 2023 (Phase 3), more than 5,000 Cubic Yards (3,800 Cubic Meters) of Ductal ultra-high performance concrete will have been installed on the New Jersey bound bridge. The Delaware Memorial Bridge represents the single largest bridge deck rehabilitation project to utilize a UHPC overlay in North America to date.
Some of the key properties of UHPC include:
- High compressive strength
- >18,000 psi (120 MPa)
- Very low permeability
- High durability
- High ductility
- High impact resistance
- Superior bond strength
- Long service life
Due to these exceptional properties, UHPC has a wide range of applications in the construction industry, including bridge construction and repair, preservation of concrete structures, precast concrete elements, architectural features, and industrial flooring.
In the United States, UHPC has been used for thin-bonded overlays and bridge deck partial-depth replacements since 2016. It has an even longer track record in Europe.
UHPC Mix development/production and associated costs
Developing a UHPC material that is suitable for use as a bridge deck overlay poses a few challenges, one being cost. The overlay application requires a relatively high dosage (>400 lbs/yd3) of expensive (and price volatile) steel fiber reinforcement which is a critical component of the mix to restrain shrinkage and control cracking. Additionally, UHPCs are typically a blended and bagged product, meaning production and freight costs need to be taken into account.
However, the use of this newer technology will provide a long-term reduction in maintenance costs and traffic interruptions. A Lifecycle Cost Analysis (LCA) of the DMB project resulted in a $65 Million savings over a period of 50 years by implementing the UHPC overlay solution.
Greg Nault, PE, SE, Ductal’s UHPC engineered technology team member, states that involvement in a project of this magnitude has propelled Ductal’s reputation to higher levels in the preservation and repair of structures industry and will open the door for other bridge owners to apply this emerging technology and solution on their bridges.
References
Ultra-High Performance Concrete (UHPC) Overlays: An Example of Lifecycle Cost Analysis, FHWA Publication No.: FHWA-HRT-23-012
