While most citizens understand that a street has to be closed if it is to be repaved, patience can falter as the closure and detour extend beyond the announced schedule. Just like when one’s home contractor announces that the kitchen remodel is going to take an additional month, that extra month of disorder is unwelcome news.
As with that home remodel, road construction projects can be delayed for a host of problems, many of which simply could not have been foreseen. Recently, SDOT’s repaving of North 105th Street, which necessitated the closure late last summer of eastbound traffic between Greenwood and Aurora on that street, was delayed when three abandoned storage tanks were found buried in the street. While no evidence of their existence had been found anywhere in the city’s records, their presence brought that section of the work to an abrupt halt as an evaluation was made of any environmental danger they might present and whether they had to be removed before paving could begin again. (Fortunately, it was determined they could be decommissioned by filling them with sand and then paving over.)
However, just like that delayed kitchen remodel, dealing with the tanks proved to be just one of a number of challenges that forced SDOT to keep delaying the reopening of those lanes. Knowing that the impacted citizens of north Seattle were anxious to see those lanes reopened, SDOT issued a traffic advisory early last month indicating the lanes would reopen the week of February 17. That was followed the next week by another advisory, this time indicating the reopening had slipped to the week of February 24. That, too, proved too optimistic, forcing SDOT to issue yet another advisory, this time indicating the change would occur the week of March 3. Fortunately, it did finally happen, but the question lingers as to why this happened and why SDOT hadn’t foreseen whatever problems ultimately occurred.
In this case, as with other projects, it was the weather that intervened. One advantage of our Northwest climate is that we don’t often have the very cold and very warm temperatures experienced by so many other parts of the nation. In fact, we’ve had a pretty mild winter, however, February brought us a serious cold snap, followed by some of the heaviest rainfall we’ve experienced in a long while. It seems appropriate to explain how weather can quickly bring a project to a halt, even when the public is pushing to see a project move ahead.
Laying asphalt isn’t unlike baking a loaf of bread, if the temperature isn’t right or there is too much water, then the final product isn’t going to meet expectations. If the ground temperature is below 45 degrees, it will be clumpy. In part, it depends on how thick the asphalt application needs to be. For example, the base layer of a street, the layer above the gravel base, asphalt can be applied at temps as low as 35 degrees. For the surface layer (on which vehicles travel), a temperature closer to 45 degrees is needed to ensure the desired smooth surface.
There is also the issue of rain. While the Pacific Northwest gets a lot of rain, it is torrential rains, such as the ones that followed the cold spell in February, which can necessitate a project shutdown. Too much water in the mix undercuts final strength of the asphalt.
Concrete, which is more expensive and lasts longer, can tolerate a little more rain and cooler temperatures. An inspector measures the temperature of concrete when the truck arrives at the job site. If it doesn’t measure between 50 and 90 degrees, it is rejected and sent back to the plant. (In addition, before it arrives on site, it can’t be mixed with an aggregate that has a temperature below 32 degrees.) While the concrete itself may fall within this temperature range, it can’t be laid on a freezing sub (gravel) base and can’t be applied in driving rains. This is particularly true for finishing work when the contractor is seeking the smoothest possible road surface.
At the other end of the temperature spectrum, we don’t lay concrete in temperatures of 90 degrees or above. The evaporation rate is simply too great in such hot temperatures, and compromises its lasting strength. Fortunately, hot temperatures aren’t a problem with asphalt. In fact, warmer weather is advantageous with asphalt.
We are fortunate that it isn’t often that Seattle temperatures are too low or too high and/or the rainfall is too heavy and forces a suspension of construction. SDOT works in close consultation with its contractors, watching the weather forecasts and making the call as to whether or not a work stoppage is necessary. In those instances where such a temporary work suspension is needed it doesn’t result in higher project costs. Instead, the contractor is given a corresponding number of additional days to complete the work.