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A separate placing boom that straddles the climbing formwork of the building core is keeping deck pours on schedule for a 60-story condominium building in Chicago. An adjacent 24-story hotel is also a part of the River East project. The towers are tied with a 4-level podium between them.

The complex will occupy a full city block, fronting at 300 E. Illinois St., between Columbus Ave. and McClurg Court on Chicago’s North Side near Lake Michigan. By mid-December the steel-framed hotel had reached the sixth floor, as a truck-mounted Schwing concrete boom pump placed all deck mix. The pump also is placing three suspended decks and a slab for below-grade parking in a top-down construction method for the expansive 220x575-ft slabs that run below both towers and the podium.

The concrete contractor, Adjustable Forms, Inc., Lombard, Ill., is building the 90,000-cu-yd project for general contractor Morse Diesel. While the remainder of the hotel building is being bucketed from the sixth level up, pumps from Anderson Concrete Pumping, Chicago, are responsible for all slabs up to Level 6 on both towers, plus the podium that was to be started February l. For the cloud-scraping, 644-ft-high condo tower, Anderson is operating a Schwing 8000 trailer pump to provide a steady supply of mix to the separate placing boom on the tower core.

Headed by Joan Andersen, the nine-year-old pumping concern got its startup as a Womens Business Enterprise. Its six-pump fleet consists of Schwing truck-mounted units with 32XL-, 39-, 42-, and 47SX-meter booms and model 4000 and 8000 trailer pumps.

Truck pumps start job Each tower has an identical footprint of l80 ft (fronting Illinois St.) by 220 ft. The podium between them is 230x220 ft. The subgrade parking decks, 575x220 ft, are poured from the top down at 6-in thick with post-tensioned beams.

"We started our deck pours at street grade by pouring half-way across with the 42-meter Schwing,"says Al Schmidt, superintendent for Adjustable Forms. "We form four construction openings of 8x45 ft for backhoe excavation and for the pump to operate simultaneously. When we complete a half-deck we drop our deck forming system to the next level down. At the same time, the separate placing boom is pouring the upper decks of the condo."

To stabilize the excavation, the contractor pumps slurry into the cavity behind the 2-ft-thick walls. Following wall pours, the tremied slurry is removed for disposal. Booming down through the construction openings, "the pump has been averaging 80 yds an hour. That’s excellent production in a confined area," Schmidt points out.

Of the total 90,000 yds of concrete, approximately two-thirds is going into the condo. Above Level 4 the all-concrete structure’s set-back design results in a tower perimeter of 114x114 ft. From this level, typical decks continue to the tower top-out above the penthouse floor. At Level 6, the separate placing boom took over for the 42-meter Schwing truck pump.

Formwork for the 34x54-ft condo tower core was built to specification for capacity and movement by Forming Concept, and site-assembled by the concrete contractor. Built with plywood, laminated beams and steel walers, the climbing system is powered by eight hydraulic jacks. A doweled keyway system ties into exterior core walls, and the outside panels move on rollers. In operation, the form moves up one level in l l/2 hours.

Adjustable Forms is placing the mix on a three-day cycle. While a crane bucket starts the tower’s perimeter walls and columns and the core’s exterior walls at 6:00 a.m., pumping with the separate placing boom starts an hour later, and continues steadily until l:00 p.m., when a full deck is completed. For the six-hour pour the placing boom is responsible for about l2,000 sq ft of deck coverage and two interior core walls, a total of 395 cu yds of mix. In addition, 60 yds of exterior core wall mix, 96 yds of column mix and 60 yds of perimeter wall mix bring total concrete yardage to 550 yds at each floor level at mid-tower height.

A reliable boom The Schwing 8000 trailer pump is supplied with a steady flow of mix from Ozinga Bros, Inc., delivering loads of 8,000- and l2,000-psi concrete. Positioned at street grade at the west edge of the condo tower near the connecting podium site, the pump is fitted with l00 ft of straightline to the core, where l0-ft sections of standpipe run vertically up the core wall. At the top of the form a 90-degree elbow directs the 5-in line to the remote boom.

The Schwing 32XL separate placing boom is positioned on an X-frame of steel beams atop the formwork at the center of the core, three levels above the deck being poured. The form is raised every third day for successive pours.

"We’re renting the pump, but we purchased the placing boom," Schmidt says. "Our company specified the make and model – we wanted a quality boom as a permanent addition to our concrete placing equipment. We’re primarily a concrete forming company, and River East is our first major concrete placing project."

By the end of the year, Adjustable Forms had completed Level 4l of the 60-story condo tower. Deck pours are completed by adding a maximum of 80 ft of line system to a spider with a 60-ft pouring radius. The method has resulted in a steady production of over 65 cu yds of slab and interior core wall concrete placed per hour.

"We’ve maintained a good production rate at high deck levels," says Schmidt. "So far, we’ve been pumping with the rod side of the pump’s rock valve, and getting good pressure even at this high elevation. We’ll be switching to the piston side when we get to the next floor or two, where we’ll want more pumping pressure."

The contractor’s crane and bucket, Schmidt concedes, "hit maximum production of 45 yards an hour at the lower levels. Now – if everything works well – we’re lucky to get 30 yards an hour."

With the pump and placing boom more than doubling the production of the crane and bucket, the all-concrete condominium building and the adjacent steel-framed hotel will add two more towers to the skyline of highrise-happy Chicago by a March l deadline.

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