Why waterproof? Safeguarding steel and concrete bridges
Crumbling roads and bridges are causing deep concern for government officials and transportation agencies around the world. Aging infrastructure, combined with increasing traffic growth, put into question the long-term viability of many rail and road bridges.
Waterproofing is one key mechanism for extending the life of these critical structures.
Bridges at risk
|3,000 council-maintained road bridges in Britain were found to be substandard.||Source:
UK RAC Foundation
|Almost 70% of Europe’s steel railway bridges are more than 50 years old, and many are in dire need of repair.||Source:
Sustainable Bridges: Assessment for Future Traffic Demands and Longer Lives, Taylor & Francis: Oxford, UK
|There are 178 million daily crossings on over 47,000 structurally deficient U.S. bridges||Source:
American Road and Transportation Builders Association
|More than half the world’s population live in urban areas, and this is expected to increase to 70% by 2050. This will put increased pressure on already overburdened bridges.||Source:
Population Reference Bureau
|The total corrosion costs for the roads and bridges in China in 2014 was 62.37 billion RMB.||Source:
The Cost of Corrosion report in Nature.com
Causes of bridge deterioration
Increasing traffic levels, the increased weight of today’s vehicles as well as increases in carbon dioxide, sulphates, sulphuric acid and chloride ions from de-icing salts are all contributing to the deterioration of existing bridge infrastructure. Both refurbishment and new bridge projects must be designed with this in mind.
Steel bridges. These bridges are at risk of corrosion through oxidation from exposure to moisture and oxygen. A cycle of deterioration is triggered once the steel begins to rust and corrode, causing further cracks and spalls that exacerbate corrosion.
Concrete bridges. Moisture and chloride exposure are the main causes of deterioration of concrete bridge decks. Over time, this ingress causes cracking, scaling and spalling and eventually erodes the steel bars within the concrete.
After surveying all U.S. state departments of transportation and Canadian provincial transportation agencies, the National Cooperative Highway Research Program found that "concrete bridge deck deterioration is one of the most extensive bridge maintenance problems effecting the service life of bridges. The use of waterproofing membranes is one strategy to prevent moisture and chlorides from reaching the concrete by providing a barrier on the top of the concrete deck. The waterproofing membrane is then protected from the traffic by an asphalt overlay."
Benefits of bridge deck waterproofing
Extending the life of new bridges: With new structures come high expectations and pressure to achieve >100-year service life and limit the need for frequent and disruptive repairs. The need for future proofing against increased complexity of design and anticipated traffic volumes are all factors adding to the challenge of bridge protection. To reduce the risk of deterioration, quality waterproofing should be discussed at the early stages of the project. The bridge deck, waterproofing membrane and surfacing need to be considered together. Achieving the optimum combination extends the life and reduces maintenance cycles, future disruption and the overall project costs.
Repair, refurbish and maintain existing bridges: The closure of busy bridges for refurbishment work can cause major and costly disruption. Incorporating a quality waterproofing system to protect aging bridges for the long term is essential in reducing ongoing maintenance and subsequent bridge closures.
What to look for in a waterproofing membrane
The type of waterproofing membrane needed may vary depending on many factors. For bridge refurbishments, there typically is a focus on reducing future maintenance and dead load and on choosing a membrane that’s quick to apply to reduce closure times. For new bridge construction projects, there is a focus on choosing a membrane that will offer long-term asset protection.
Some important factors to consider when comparing waterproofing systems include:
- Length of bridge closures and/or night possession
- Phasing of works
- Preventing costly overruns
- Climate conditions and environmental challenges
- Type and depth of proposed paving
- Condition of the deck
- Longevity of the waterproofing membrane
- Availability of reference sites for similar projects
- Transportation Infrastructure