Arch rib photo story part 4 of 4

From ODOT-In the past few weeks, we have explored how the Willamette River Bridge deck arches are built. We started with the steel-reinforced shafts that provide a support for the arches. Then, we described the intricate work to connect the arches with the foundation. Next, we saw the skeletal elements of the arches. Now we will see what gives the arches their strength and makes up the part that is actually visible. The picture at the top of our blog page can help you visualize the finished arches.

With the rebar arch skeleton in place and the first of the arch forms built, trucks started lining up to provide a constant supply of fresh concrete to pour the arches. The intricate twists and bends of the rebar cages create a challenge: Air bubbles, poor mixture or inconsistent filling of the form can lead to weaknesses in the concrete, compromising the integrity of the arch. To avoid this, the team brought in a local concrete-mixing expert to oversee the process. This speciality contractor developed a variety of "concrete cocktails" that resulted in a mixture capable of flowing almost like water to fill every nook and cranny within the arch form, yet able to strengthen enough to support the bridge.

Next: Watch for the crown pouring and the jacking of the arches.