by: DAVID F. ASHTON - These plumbers are preparing the piping system that will circulate cooling water inside the concrete columns, while the Bent 6 cap beam high-strength concrete cures.As contractors focused on the west side approach for the new Sellwood Bridge, work slowed on the east side of the Willamette River.

Throughout April, divers kept plugging holes in the mid-river leaky “Bent 5 box caisson”.

The most apparent work was atop Bent 6, the full-width pier built to support the bridge deck as it lands on the east side of the river.

“We’re getting ready to pour the cap beam,” explained Multnomah County Inspectors’ Manager Mark Knieriem. “It will be about 125 yards of ‘6,000 pound’ concrete.”

This high-strength concrete has compressive strength generally greater than 6,000 pounds per square inch, THE BEE learned. It’s made by lowering the ratio of water-to-cement; and often silica fume is added to prevent the formation of free calcium hydroxide crystals in the cement matrix, which might reduce the strength at the cement-aggregate bond.

“This high-strength concrete generates quite a bit of heat while it cures,” Knieriem said. “That’s why workers are running cooling tubes through rebar, and hooking it up to water manifolds.”

The rebar sticking up above the Bent 6 concrete forms (which look like lobster traps) will form columns that will keep the pre-cast longitudinal girders in place, as they ride on bearings during a seismic event, Knieriem explained.

The rebar boxes on either end of Bent 6 will be incorporated into the bridge’s parapets. “This gives a good idea of the exact width of the bridge, as it lands on the east side,” Knieriem said.

The project’s spokesman, Mike Pullen, said contractors now expect that the pre-cast beams for the east side landing will be delivered and installed sometime in May.

“This will require some type of bridge closure. We don't know if the closure will be for a few hours, or a day, or what day of the week.” Subsequently, the County announced a closure during part of the week of May 12. Signs giving the expected dates have been posted.

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