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July 2002 - Form work for exterior walls and dredge wells at Pier 37; initial form work for Pier 38
Pier 37: The walls of the caisson box reach a height of approximately 30 feet (9.1m) as another level of forms is hoisted atop the perimeter of the cutting edge. Note the breakwater structure behind the forward wall.
The floating cutting edge has begun to sink in the water, under the weight of poured concrete. The interior floor is now below the water line, which is located roughly between the two walkways.
Forms for concrete are located behind the blue vertical beams. Bare concrete is visible where forms and brown burlap covers used for curing have been removed.
The top of the new concrete wall, one day after the pour. This upper edge is cleaned and impurities from the pour called "laitance" are removed before the next level or "lift" is poured. The rough gray material is aggregate in the concrete, which helps to form a good bond with the next lift.
"Gang forms", located behind the blue vertical supports, are hoisted to the next level. Compare the forms in the middle of the picture with those at the far left. 20 to 30-foot sections of gang forms are joined together to form one large sheet, and are hoisted into place with a crane.
Brown burlap curing blankets, which are hung as soon as forms are removed, are clearly visible in this photo. These blankets remain in place for a week and are kept wet to reduce evaporation of water from surface of the concrete. Rapid evaporation and drying can cause shrinkage cracking at the surface while the concrete underneath is still wet -- similar to what happens when mudflats dry out.
Pier 38: View from the top of the caisson's perimeter, with the breakwater visible behind the forward wall. Compare the depth of this caisson box with that of Pier 37.
Workers prepare for concrete pours now that the second cutting edge is in place.
A welder uses a towel to shield himself from the hot Mississippi sun.
The downstream caisson guide is visible behind the rear wall of Pier 38.
Pier 37: The round pipes are concrete forms for dredge wells, the openings through which soil will be removed when the caisson reaches the river bottom.
Concrete forms for dredge wells. The octagonal wooden cover atop the form at right rear is the first of the work platforms to be installed. Workers will stand atop these platforms as they vibrate freshly poured concrete into place. The platforms also provide safety by covering the dredge well openings.
Both cutting edges have 24 dredge wells. Each steel dredge well form is 14 feet (4.2m) in diameter. Concrete is poured around the forms and the center is left hollow; the forms are removed and reset atop the new concrete, and the round dredge shafts grow taller with each pour.
Fitting a round peg into a square hole -- or is that the other way around? The round dredge well forms sit on plywood "soffits", which provide a smooth structural transition between the square air-domes at the bottom of the grid-shaped cutting edge and the round design of the dredge wells.