Bridges are an integral part of our nation’s transportation and economic infrastructure, and their maintenance is essential to maintaining commuter safety as well as economic livelihood. The collapse of the I-35W Bridge in Minneapolis last August is a high-profile example of the tragedies that can occur when bridges fail.
Without properly maintained bridges, low-cost corn could not move safely and efficiently from the Midwest, across the mighty Mississippi River and to the east coast of the U.S. Likewise, Pittsburgh never would have grown to be an international force in the steel industry or an up-and-coming star in biomedical technology without bridges to transport materials, as the city is home to many bridges that span three converging rivers.
Another city that depends so heavily on these elevated roadways is Chicago, home to the U.S.’s largest gathering of movable bridges, as well as hundreds of other nonmovable, standard bridges that span the Chicago River and other local obstacles.
Recognized worldwide as “The Windy City,” Chicago also holds a lesser-known nickname, “The City That Works,” for its bustling economy and the impact it has on the world stage. Chicago, and its citizens, has built this reputation based on hard work, determination, tenacity and an uncanny ability to succeed.
None of this would be possible without the many bridges that span the city’s waterways and link it with the rest of the country and, ultimately, the world. It is this linkage—keeping goods and people moving freely into, and out of, the city—that makes bridges so important to Chicago and many other communities throughout America. A recent repair project on the East Randolph Street Bridge in Chicago is proof that this city is committed to maintaining its road system and reducing its odds of having to experience the horrors that took place in Minneapolis last summer.
A membrane that works
Located in the heart of downtown Chicago, the East Randolph Street Bridge is a concrete structure that spans two roadways and a commuter rail station. Over the past several years, the bridge experienced significant water damage, and a face-lift was necessary before things got out of hand.
The primary factor in the bridge’s slow demise had been a poor-performing waterproofing system that was installed only five or six years ago. A standard deck coating commonly used on bridges and other automotive-bearing structures throughout the U.S., the waterproofing system on the East Randolph Street Bridge was severely damaged and the bridge’s concrete supports were likely to follow if a more long-term replacement was not installed.
City officials decided that the most economical solution to get the bridge back to a high level of performance was to replace the waterproofing system and pave the surface with a polymer-modified asphalt. This unique type of asphalt helps reduce cracking, thereby protecting the waterproofing system and the underlying concrete supports.
Officials involved with the project did not want to install a similar traffic deck coating to repair the bridge due to the poor performance record of the last system. There also was another issue that made a similar replacement impossible for the re-waterproofing of the bridge—time.
“We were working under a significant amount of pressure, because the Randolph Street Bridge handles a lot of the daily traffic into and out of the city,” said Scott Pine, vice president of Pine Waterproofing and Sealant from nearby Northfield, Ill., the contractor in charge of re-waterproofing the six-lane concrete bridge. “We had to work through the night so we were out of the way by the time morning rush hour rolled around, and there’s no way that would have been possible with a typical coating.”
To ensure that everything was completed on time, Pine decided that a self-adhering waterproofing membrane was the best option for replacing the failing coating, and he chose a product he had used on numerous projects in the past—CCW-711. Manufactured by Carlisle Coatings & Waterproofing Inc., CCW-711 is a 65-mil-thick, self-adhered waterproofing membrane consisting of a rubberized asphalt laminated to a high-strength, heat-resistant, woven polypropylene mesh.
It was designed specifically to waterproof the structural slab of bridges and parking decks that are to be overlaid with asphalt paving. This unique product not only protects the concrete structure, but it also helps reduce cracking in the asphalt pavement itself, which extends the life of the entire bridge.
“Self-adhering waterproofing membranes are ideal for projects on very tight deadlines because paving can begin immediately after the installation of the sheet,” said Pine. “Alternative coatings take much longer to cure and require significantly more downtime, which was not an option for this project.”
The project was broken into two sections to ensure that everything was completed and out of the way by the next morning. Contractors worked on one half of the road on the first night and the second half on the next night. They had 10 hours, from 8 p.m. to 6 a.m., to finish each night’s work.
The two-day project began when Sanchez Construction Services from Chicago removed the existing road surface, exposing the concrete substructure that needed to be waterproofed. After the old asphalt was removed, Pine Waterproofing began their portion of the repairs. They started by pretreating the most heavily damaged sections of the bridge, where severe cracks had formed. To do this they installed a hot-rubberized asphalt waterproofing system that filled in, and sealed, the large cracks.
While the CCW-711 elastomeric, self-adhering membrane features a woven mesh that ensures both strength and flexibility to span moving cracks without degradation, Pine opted for the redundant protection of the rubberized asphalt just to be safe.
“Typically I would not have specified the additional rubberized asphalt, but this bridge has a long history of leakage problems and I wanted to provide the city with a durable solution that was sure to last a long time,” said Pine.
The rubberized asphalt was poured out of 5-gal buckets directly onto the concrete and spread over the cracks with squeegees. After the most heavily damaged areas were filled, covered and treated with hot rubber, Pine’s crew cleaned the entire surface and applied a primer with 9-in. rollers. The primer ensured that the self-adhering waterproofing membranes would form a strong bond between the sheet and the concrete surface of the bridge.
Pine Waterproofing completed their portion of the bridge project by installing the self-adhering membranes and applying a layer of hot rubber to the overlaps for additional protection at the most vulnerable areas. To install the membrane, workers laid the 24-in. x 100-ft rolls onto the bridge, peeled off the siliconized release liner and set them back into place. Per installation instructions, Pine Waterproofing overlapped the edges by 21/2 in., and then rolled the sheets with a rubber tire to activate the adhesion.
Immediately after the final sheet had been installed, the specialized polymer-modified asphalt was applied directly over the top of the membranes to create the finished road surface. Within only a few short hours the entire bridge was completely open to the public, and the daily dose of morning commuters were safely buzzing over the structure, giving little thought to the work that had just been completed.
“Waterproofing systems are key to the performance of any bridge, but most people do not even think twice about what’s protecting these structures as they traverse them on a daily basis,” said Pine. “We are proud of the work we do, and staying out of people’s way while we do it is a key part of our success. Without the advent of self-adhering membranes, we would not have been able to complete this project, and many other projects, in a timely manner.”
And timely is what bridges are all about, because without them it would take a lot longer to safely get to work or school or to ship goods from one place to another. While catastrophic events such as last year’s collapse of the I-35W in Minneapolis garner widespread attention in the press, it is the day-to-day maintenance projects performed by companies like Pine Waterproofing that should be making headlines.