There are 614,387 bridges in the United States, and almost 40 percent of them are more than 50 years old. Many of these bridges are showing their age, with more than 9 percent of bridges classified as structurally deficient according to the American Society of Civil Engineers (ASCE) 2017 Infrastructure Report Card.
Bridge maintenance and repair projects extend the life of these structures, but a backlog of bridge repair work has accumulated. The cost to repair America’s deteriorating bridges is estimated at $123 billion.
It is imperative that the most cost-effective bridge maintenance techniques are employed to keep overall project costs down. Innovative materials and techniques are being used to not only increase the lifespan of bridges, but to decrease the total lifetime cost of these structures.
Why bridge maintenance is critical for American infrastructure
The United States received a “C+” for bridges in the 2017 Infrastructure Report Card. As of 2016, one in eleven bridges was rated structurally deficient—requiring significant maintenance, rehabilitation, or repair. The good news is this number is slowly declining, thanks to increased awareness of the importance of reliable bridges for both safety and economic health.
The states with the fewest number of structurally deficient bridges based on percentages are:
- Nevada—1.6 percent
- Texas—1.7 percent
- Florida—2.1 percent
- Arizona—2.6 percent
- Utah—3.14 percent
The states with the highest percentages of structurally deficient bridges are:
- Rhode Island—24.9 percent
- Iowa—20.5 percent
- Pennsylvania—19.8 percent
- South Dakota—19.6 percent
- West Virginia—17.3 percent
America’s bridges are old, with an average age of 43 years. The expected lifespan of these bridges is 50 years, which means many of them (even those not yet designated structurally deficient) will soon be in need of major repairs and rehabilitation.
More than 13 percent of bridges were found to be structurally obsolete. These bridges are unable to meet the current traffic demands or standards. For example, there may not be enough lanes on the bridge, the lanes may be too narrow, or the shoulders on the bridge may not be wide enough. Functionally obsolete bridges add to increased traffic congestion and the associated pollution.
Several recommendations were listed in the Report Card in order to raise America’s bridge grade, including:
- Increased government funding for bridge repair and maintenance projects.
- Considering the costs across a bridge’s entire lifecycle during design to minimize future maintenance and repair needs.
The 2018 Deficient Bridge Report published by the American Road & Transportation Builders Association (ARTBA) further demonstrates the poor state of US bridges. The report found that Americans cross these 54,259 structurally deficient bridges a total of 174 million times each day. One in three US bridges have some type of identified repair need.
At the current rate of repair, the report estimates it would take 37 years to correct all issues. This is simply unacceptable. New and innovative approaches are needed to increase the lifespan of bridges and decrease the lifetime cost of bridge structures.
Innovation and cost-effective bridge repair and maintenance techniques
It is always more cost-effective to be proactive rather than reactive when it comes to bridge maintenance. A proactive approach extends the life of bridges. It also identifies problems when they are small—and small problems cost less to fix.
Proactive bridge maintenance involves preservation and preventive maintenance activities. Bridge preservation prevents and delays deterioration. The focus is on keeping the bridge in good condition and addressing any minor problems as soon as they are discovered. A proper preservation program uses cost-effective techniques to extend the life of bridges, therefore lowering the total lifetime cost of the structure.
Preventive maintenance is part of a comprehensive bridge preservation program and can be broken down into cyclical and condition-based activities. Cyclical maintenance should be done on a routine basis to preserve the existing bridge and its components. Activities include:
- Washing (1-2 years)
- Sealing deck joints and cracks (3-5 years)
- Lubricating bearings (2-4 years)
- Coating steel beam and girder ends (10-15 years)
Condition-based maintenance is performed as needed. Issues are usually identified through routine bridge inspection and include:
- Deck patch and repairs
- Bearing restoration
- Repairing or installing new expansion dams on bridge decks
- Guardrail repair
- Retaining wall repair
- Drain repair or replacement
- Concrete deck repair
A full list of these and other bridge maintenance activities is provided by the Federal Highway Administration (FHWA).
Bridge rehabilitation encompasses larger projects to correct the structural integrity of a bridge. Examples include:
- Partial or complete deck replacement
- Substructure strengthening
Eventually, older bridges may require a total bridge replacement. The new bridge must meet construction and structural standards and be able to satisfy the demands of the projected traffic pattern.
Proper bridge preservation and preventive maintenance make rehabilitation and replacement projects less frequent, saving money and extending bridge life. Innovative materials and techniques are being used in bridge maintenance, rehabilitation, and replacement to decrease the lifecycle costs and increase the longevity of bridges.
Embedded sensors are being employed in both new and existing bridges to monitor structural conditions. Sensors detect damage caused by traffic, wind, temperature, vibration, and other environmental factors.
Continuous monitoring makes it possible to address issues before they become a serious problem, decreasing overall repair costs and increasing the lifespan of a bridge. The Memorial Bridge connecting Portsmouth, NH to Kittery, Maine is an example of a bridge benefitting from embedded sensors.
Ultra-High Performance Concrete (UHPC) is a new concrete technology that is extremely strong and durable. UHPC is being used in many bridge repair and maintenance projects to add strength to existing bridges and increase the lifespan.
UHPC has an estimated longevity in excess of 75 years, so using it in bridge repair and maintenance projects dramatically increases the structure’s longevity. It is ideal for use in bridge girders and decks, increasing the strength and durability of these components.
UHPC is also being used in seismic columns for bridges, due to its ability to withstand earthquakes. This new concrete is ideal for pier pilings given the material’s resistance to moisture and environmental degradation.
While UHPC may require a higher upfront cost, less material is required overall and the increased lifespan of UHPC translates to a lower overall lifecycle cost. This makes it a cost-effective choice for bridge concrete repair and maintenance.
Prefabricated bridge elements and systems (PBES) are structural components of bridges built off-site. Once ready, they are moved to the construction site for installation.
This reduces on-site construction time, decreasing pollution and traffic congestion during bridge repair and maintenance projects. UHPC is an ideal connector for PBES, creating a stronger and more durable bond, and it is often used for these structural components.
As America’s bridges continue to age and deteriorate, innovation is the best way to address the necessary repairs and maintenance, while also keeping costs to a minimum. New approaches and materials such as embedded sensors and UHPC are increasing the life of existing bridges, making new bridges stronger and more durable, and decreasing the overall lifetime cost of bridge structures and components.
Source: https://beeldbank.rws.nl, Rijkswaterstaat