Tuesday, August 13, 2019

Rain dampens SR 99 Aurora bridge paving schedule

By Tom Pearce

Many of our projects can deal with a little bit of rain. When it comes to repaving bridges, though, dry weather is critical. That's why last week we had no choice but to postpone work on Seattle's SR 99 Aurora bridge. Now our plan is to pave the next two weekends, Aug. 17-18 and 24-25.

During paving, traffic will be reduced to one lane in each direction across the bridge from 7 p.m. each Friday until 5 a.m. each Monday, the same as during weekend-long lane reductions in June.

Thinking about this rain delay, I was struck by the irony. When we announced this project schedule, I thought dry weather for two whole weekends in June was pretty optimistic and July and August weekends were more realistic. Two months later, here we are – the June weekends came off fine, and we've postponed weekends in July and August due to rainy forecasts.
Waterproofing material keeps water from corroding rebar in the concrete deck.

Why do we need a dry full weekend?
To install waterproofing between the concrete deck and asphalt pavement used by more than 40,000 vehicles a day, the deck needs to be completely dry. If there's even a little moisture, the waterproofing could fail. That can lead to water getting into the concrete deck, which can corrode the rebar inside and weaken the deck structure. So even a little rain can be a big problem.

Now we're hoping for a couple of dry weekends in late August to help us finish this project. We still have several weekends of paving scheduled to remove the old asphalt, inspect and repair the bridge deck, then repave the bridge.
Once the asphalt is removed, crews can repair the concrete deck,
an original part of the bridge that opened in 1931.

Several more weekends may be necessary
The deck repairs are the wild card – until we scrape off the asphalt, we don't know the condition of the deck that was poured more than 88 years ago. If it only needs some basic patching, that's fine, we can do that right away and repave. If we find the deck needs larger repairs, it will require more time and more weekends.

This work is part of our effort to pave all of SR 99 between Roy Street near the Seattle Center and North 145th Street at the Seattle-Shoreline city limit. Most of the paving is being done on weeknights. Bridge repairs and installing the waterproofing requires too much work to do overnight, so we use weekends when traffic isn't quite as heavy.

We will complete this work, we'll do it right and we hope to complete it this year. As long as the weather cooperates.