Named after one of America’s most famous iron workers, who gained notoriety after surviving a fall from the Golden Gate Bridge in 1936 and died in 2000 at age 95, the Al Zampa Memorial (New Carquinez) Bridge is the first major suspension bridge to be built in the U.S. for nearly 40 years.
With a span of 3,464 ft and a width of 89 ft, the deck, which was to sit 140 ft above the water, carries four lanes of vehicular traffic including a high-occupancy vehicle lane together with a pedestrian/bicycle lane. This handles all westbound traffic on I-80 between Vallejo and Crockett, Calif., while all eastbound traffic travels over the remaining 1958 bridge.
Located some 20 miles northeast of San Francisco on three different active earthquake faults—the San Andreas Fault, the Hayward Fault and the Franklin Fault—seismic resistance was a critical consideration for the new bridge. Caltrans required the bridge to be designed to withstand the maximum credible earthquake from each of the three faults. Based on the Richter Scale these were given as 8.0 for the San Andreas Fault, 7.25 for the Hayward Fault and 6.5 for the Franklin Fault, making it the first-ever U.S. bridge to be designed to such stringent seismic standards.
Stern by nature
By their very nature, steel orthotropic decks are a stern test for any waterproofing system. Not only are they livelier than conventional truss-stiffened concrete decks but they also are subject to a greater level of expansion and contraction, because the heating and cooling cycle of a steel deck is considerably quicker than that of a concrete deck. Additionally, because of the need to reduce the dead load on this type of bridge, thin asphalt surfacing tends to be used with higher application temperatures than conventional surfacing.
These characteristics, allied to a heavily trafficked bridge for which lane closures would not be acceptable, and a structure that by its very nature can necessitate high maintenance access costs, all pointed to the need for the very highest level of protection for the deck against corrosion. Parsons’ recommendation to Caltrans was Stirling Lloyd’s Eliminator bridge deck waterproofing membrane and SA1030 bond coat. Parsons witnessed the system’s benefits on previous successful collaborations including the Queensboro and Williamsburg Bridges in New York, the latter being a steel orthotropic deck.
Importantly, Stirling Lloyd could point to a proven track record of successful applications on orthotropic steel decks both in North America and around the world. Structures protected include the George Washington Bridge that links New York and New Jersey, the Mackay Bridge in Nova Scotia, the Forth and Severn road bridges, the Tsing Ma Bridge and the two Bosporus Bridges linking Europe and Asia.
The waterproofing method chosen was a rapid-curing, seamless, spray-applied membrane based on methyl methacrylate (MMA) resins with approvals from highway and rail authorities around the world. The system’s physical and in-situ performance properties would provide the solution to a number of potential problems facing the consulting team.
The large deck and air temperature fluctuations experienced could be readily accommodated by the system, and the Bay-area sea fogs would not affect its cure, provided that the deck temperature was above dew point. The system’s speed of application and cure, together with its toughness, would solve the issues of an increasingly tight application schedule and the need for construction vehicles to travel on the membrane shortly after application and on an ongoing basis.
The ability to overcome these potential problems resulted in the waterproofing system being specified for the new bridge deck.
Following a competitive tender the FCI-Cleveland Joint Venture awarded the contract to apply the system to the 285,000-sq-ft deck to Venture Construction of New Hampshire.
Yellow and gray makes protection
The waterproofing of the deck was undertaken in three phases, with the first beginning in May 2003. This involved the waterproofing of the edgeworks, upstands and the deck area on which the concrete crash barrier, separating the bicycle/pedestrian lane from the main deck, would be cast.
Venture arrived on site at the end of May 2003, with their first job being to prepare the new deck. This entailed shot blasting the deck to a SSPC SP10 near-white metal blast finish. Once blasting had taken place tensile adhesion tests were carried out to ascertain the bond strength of the membrane to the substrate and confirm satisfactory surface preparation.
Within four hours of blasting, a team from Venture commenced application of a fully reactive methyl methacrylate primer to the deck. Specially designed for metal substrates the primer protected the freshly blasted steel work from corrosion and enhanced the adhesion of the subsequent membrane.
The waterproofing membrane application could begin within 30 minutes of the primer application. The membrane was spray applied in two color-coded coats. The first coat is colored a light yellow to enable visual identification during spraying, ensuring that the specified thickness of 50 mils was applied. Additional quality assurance was provided by wet film thickness checks, using a wet film thickness gauge, to ensure the specified thickness of 50 mils was achieved.
The membrane’s rapid cure and durability meant that within one hour the membrane had fully cured, could be inspected and application of the second coat started, despite the need for construction vehicles to be able to travel on the first coat. The second coat was colored gray, contrasting with the color of the first coat to provide a further visual aid in ensuring correct coverage. Again wet film gauge readings were used to confirm the required coat thickness of 50 mils to give a final membrane thickness of 100 mils.
The application was carried out by three sprayers working side by side, operating from one pump giving high daily outputs.
Upon completion and inspection of the second coat, application of the SA1030 bond coat began. SA1030 is a proprietary, hot-melt, solvent-free adhesive based on a polymer-modified bitumen, engineered to provide a very strong bond between the membrane and the surfacing.
The bond coat was heated to the required application temperature of 350-390°F. It was then poured onto the deck and distributed by straight bladed squeegee to give the required thickness of 40 mils. Within 30 minutes, the bond coat had cooled and was ready to receive the surfacing.
The 280-325°F at which the asphalt surfacing was laid activated the bond coat, which then as it cooled provided a strong long-lasting intimate bond between the waterproofing membrane and the wearing course.
The materials and method of working used on this phase of the job were then repeated on the subsequent phases of the project. The second and largest phase of the work began in early September entailing the waterproofing of the roadway area of the deck. Added complications on this part of the project included strong crosswinds and the requirement to keep one lane open for site traffic at all times. However, the speed and simplicity of this application had workers applying up to 21,520 sq ft daily, completing some 236,000 sq ft in 18 days.
Once this phase had been successfully completed in early October, the third and final phase, encompassing the bicycle/pedestrian lane commenced and was completed in just two days.
The completion of the project on time was of the utmost importance and the rapid spray application and fast cure ensured that the waterproofing work was carried out well within the given time frame, ensuring no time-consuming and potentially very costly delays.