BY JASON ARMSTRONG, PRODUCT MARKETING MANAGER – LIQUID WATERPROOFING EMEA GCP APPLIED TECHNOLOGIES, A MEMBER OF MULTIPLE AGC CHAPTERS
Harsh weather conditions can be a challenge for bridge construction and renovation projects, in more ways than one. Both concrete and steel bridges are susceptible to corrosion from water and waterborne contaminants, which can impact their service life. This means selecting the best waterproofing solution is crucial. However, knowing what to look out for when selecting a waterproofing system isn’t always easy.
THE VIEW FROM THE BRIDGE
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. Corrosion of reinforcement due to chloride-ion contamination in reinforced concrete bridge structures is known to be one of the major causes for deterioration in highway bridges.
Extremes in cold, heat and even humidity are a major factor in bridge construction and renovation — often throwing project schedules off course. Some bridge waterproofing membranes are extremely sensitive to moisture and have a limited temperature and humidity application window. This can leave work crews waiting around at the mercy of the weather, leading to lost productivity, delays to construction schedules and revenue loss.
GETTING TO THE ROOT OF THE PROBLEM
Increasing traffic levels, the larger size of today’s vehicles as well as upticks 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, leading to loss of strength and integrity of the structure.
- Concrete bridges
Moisture and chloride exposure are the main causes of deterioration of concrete bridge decks. Over time, this ingress causes the steel reinforcement to corrode resulting in cracking and spalling of the concrete.
Concrete bridge deck deterioration is one of the most extensive bridge maintenance problems affecting 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.
A FORWARD-THINKING APPROACH
With new structures come high expectations and pressure to achieve a greater 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 considered 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.
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, typically there 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.
KEY FACTORS TO CONSIDER WHEN COMPARING WATERPROOFING SYSTEMS:
- Longevity of the waterproofing membrane
- Condition of the deck
- Type and depth of proposed paving
- Length of bridge closures and/or night possession
- Phasing of works
- Preventing costly overruns
- Climate conditions and environmental challenges
- Availability of reference sites for similar projects
When it comes to waterproofing bridge decks, it’s easy to assume that all liquid waterproofing systems are the same. Here are key questions to ask when specifying liquid waterproofing to ensure you get a system that’s durable and can be applied quickly, to help keep the bridge project on track.
- How quickly can the waterproofing membrane be applied?
Choosing a bridge waterproofing membrane that can be sprayed on fast and cures quickly is the first step. However, the real application time often comes down to what weather and temperature restrictions there are for applying the waterproofing system. Many liquid waterproofing systems are highly sensitive to moisture.
Unfortunately, this means applicators have to wait around for the right weather conditions before they can apply the waterproofing. This puts added pressure on bridge owners, who may face complaints from the public the longer construction or lane closures go on. Choosing a waterproofing system that is less moisture sensitive helps avoid these delays. This can also be highly beneficial for contractors, who are often rewarded, based on completion time.
2. How do I ensure the waterproofing membrane is applied correctly?
Your waterproofing system is only as good as those who are applying it. Ask potential bridge deck waterproofing manufacturers if they have an approved contractor program and how their contractors are selected. Be sure to get references for projects that are similar to yours.
It’s equally important to find out how and when quality control measures are taken. For example, spraying on the liquid waterproofing at the right thickness is essential to performance. Applying too thin a layer will compromise the physical performance of the membrane and applying too thick a layer may stress the bond of the paving.
Applicators should follow on-the-spot quality control measures, so they can quickly identify and resolve any issues. It is important to ensure you have the appropriate film thickness, measurable at the time of application. A two-coat system makes it easy to spray at the correct thickness. Tensile adhesion test, – wet-film thickness tests, and electrical integrity testing are also performed throughout the application process.
3. How easy is it to repair the bridge deck waterproofing membrane?
Bridges are busy sites that have open exposure to a host of contaminants, not to mention multiple trades working together simultaneously. It’s best to choose a bridge deck waterproofing system that can be repaired on-the-spot if the membrane does get damaged. This helps keep the bridge construction on track.
4. How do you test the performance of your waterproofing system?
In many regions, there are independent organizations that validate the performance characteristics of bridge deck waterproofing systems.
5. Can you demonstrate that your bridge deck waterproofing membrane stands up over the years?
Ask manufacturers both for references from long-term bridge projects as well as accelerated age testing data to see how the membranes have performed over the ensuing decades since they were applied.
BRIDGING THE GAP DELIVER LONG-TERM RESULTS
In summary, a carefully considered approach to specifying bridge deck waterproofing is crucial in today’s world where extreme and often variable weather conditions are on the rise, causing an increase in cases of bridge deterioration. Growth in population in urban environments is also putting increased pressure on bridges, so protecting structures to ensure a longer service life is more important than ever. Not all waterproofing solutions are the same, however, so it’s important to look for systems with a proven track record, accreditation and fast-curing systems that will enable quick and smooth installation to facilitate the wider construction work at play. Finding a company with experts on hand to guide you through the specification is a good way to ensure the plans are fool-proof and tailored to the specific project.