Ultra-High Performance Concrete Is Advancing More Resilient U.S. Infrastructure

The long-term resilience of American infrastructure depends on smart investments towards cutting-edge construction materials, which is where ultra-high performance concrete (UHPC) is making a significant impact in the nation’s transportation infrastructure.

UHPC is five times stronger than conventional bridge deck concrete, 10 times more resistant to wear and 100 times more resistant to deterioration due to corroding reinforcement and is steadily becoming an ideal solution to repair and rehabilitate deteriorating highway infrastructure nationwide.

The Delaware Memorial Bridge UHPC Deck Rehabilitation Project, for which WSP served as the designer, is a major milestone in the adoption of UHPC for major transportation endeavors. But the possibilities extend to even more infrastructure sectors.

“UHPC is a sustainable and ultra-high-performance substitute for conventional concrete in new construction, and a uniquely valuable material for infrastructure repair and rehabilitation,” said Michael McDonagh, a WSP vice president of structural engineering. “This is why we’re seeing its use growing in U.S. transportation infrastructure, but infrastructure owners in other sectors should note the potential for their own respective sectors.”

What is Ultra-High Performance Concrete?

While the word “concrete” is in its name, UHPC is actually a cementitious composite material, characterized by an optimized gradation of granular constituents, a water-to-cementitious materials ratio less than 0.25, and a high percentage of discontinuous internal fiber reinforcement, according to the Federal Highway Administration.

Research into UHPC first began in Europe in the early 1970s and UHPC saw some of its first uses in civil infrastructure in the 1990s. It first became commercially available in the U.S. in 2000.

In 2020, the ACI Materials Journal from the American Concrete Institute published a technical paper called “Performance of Ultra-High Performance Concrete in Harsh Marine Environment for 21 Years.” In this study, laboratory testing was conducted to determine the UHPC chloride content, compressive strength and microstructure, as well as corrosion of embedded steel bars over a 21-year period of marine environment exposure.

The results showed that, compared to conventional concrete, UHPC has a significant sustained increase in resistance to chloride penetration. The corrosion rate of steel bars embedded in UHPC was negligible and hence dramatically lower than that of steel embedded in other types of concrete.

“UHPC not only exhibits exceptional mechanical properties but also mitigates the intrusion of aggressive species such as chloride ions and the subsequent attack of steel reinforcement,” the paper states.

Standing Tall for Longer

The Delaware Memorial Bridge UHPC Deck Rehabilitation Project is the first application of UHPC over the entire deck of a suspension bridge and long-span bridge in North America. The top two inches of the concrete deck were removed and replaced with UHPC. Despite the fact that UHPC usually replaces some of the deck concrete, this application is often simply called a UHPC overlay.

The work began in 2018, when the Delaware River and Bay Authority (DRBA) commissioned a detailed evaluation of the four lane, 51-foot-wide deck on the oldest of its approximately two-mile-long twin suspension bridges that carry Interstate 295 between Delaware and New Jersey. Deck maintenance costs were increasing annually and deck repairs were only lasting 10 years or less on the then 50-year-old deck.

On behalf of the DRBA, WSP performed the detailed bridge deck evaluation study, and, with only two small UHPC overlays completed in the U.S. prior to the survey, determined that the entire bridge deck would need to be replaced within five years, or a traditional concrete overlay could be installed to delay deck replacement by just ten more years. Following a workshop held by the DRBA involving industry leaders, the agency became interested in the possibilities of a UHPC overlay to extend the life of the bridge deck instead of replacing it, despite the relative lack of industry adoption at the time.

In 2019, WSP performed a study for the DRBA on the benefits of UHPC overlays for the northbound bridge.

“Our study showed that a UHPC overlay could provide the existing bridge deck with additional service life on par with a new bridge deck, with significant reductions in cost and traffic disruption compared to deck replacement,” McDonagh said. “UHPC also provided the best value compared to other overlay materials.”

Based on this study, and with the adoption of UHPC overlays beginning to accelerate in the industry, the DRBA worked with WSP designers to pursue a UHPC overlay construction pilot project in the fall of 2020, which assessed the technology on three different areas of the bridge totaling 25,000 square feet of deck.

The success of that pilot project was followed by a full UHPC overlay for the entire 550,000 square foot deck on the northbound Delaware Memorial Bridge.

“According to our engineer’s estimates, the UHPC overlay installed in 2022-23 will extend the service life of the bridge deck by at least 40 years while providing a maintenance free bridge deck,” said Shekhar Scindia, technical principal for bridges at the DRBA. “This will save the agency significant costs over time, UHPC is a long-term investment that will pay significant dividends well into the future.”

“The collaborative efforts between the DRBA and WSP teams have showcased an innovative and cost-effective deck preservation strategy utilizing UHPC,” added Abate Tewelde, WSP vice president and project manager. “This groundbreaking approach now stands as a viable option for other bridge owners to explore and adopt.”

By applying properly designed UHPC at the optimal stage of deck deterioration, Tewelde said they are able to breathe new life into ageing bridge decks—often the most vulnerable component of a bridge.

“What we achieved on the Delaware Memorial Bridge serves as a living example, and a model that can be replicated on tens of thousands of bridges,” Tewelde added.

Meeting Challenge with Expertise

UHPC is not without its challenges. The material is more expensive than conventional concrete and it requires a higher level of expertise to implement. However, costs are expected to decrease as higher volumes of UHPC find applications on major infrastructure projects.

But despite these challenges, when new designs take advantage of the unique properties of UHPC, the resulting projects will often use much less material, making them less expensive and more sustainable than using conventional concrete.

Furthermore, as the Delaware Memorial Bridge deck rehabilitation project has shown, UHPC can be used to substantially extend the service life of existing infrastructure, resulting in long-term cost savings versus infrastructure replacement, along with sustainability benefits by using significantly less material with much shorter construction durations.

U.S. infrastructure owners seeking to improve the lifespan of their assets would benefit from the potential upsides of UHPC – even outside of bridges and other transportation projects.

“Many of the proven UHPC applications in transportation can be effectively adapted to other infrastructure sectors, such as industrial ports with structures and pavement supporting heavy loads while also being exposed directly or indirectly to seawater, energy facilities exposed to corrosive chemicals and vapors, and dams and water conveyance structures that would benefit from significantly reduced permeability and increased wear resistance” McDonagh said. “These investment opportunities can provide long term value for construction in many different sectors, and with returns lasting generations.”

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