Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.
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TEXAS-SIZED PILES Eagle Lake, Texas-based Valley Prestress Prod- ucts was recently awarded a contract for the prestressed products for the Copano Bay Bridge in Rockport, Texas. The entire project is about 3.5 miles long, with a two-mile bridge valued at $78 million. The prestressed products included TxDOT 63-in. beams for the 150-ft. center span, TxDOT 54-in. beams, flat slabs and 54-in. cylindrical piles that vary in length from 83 to 168 ft. Although Valley Prestress has produced precast products for a number of significant bridge and highway projects in Texas and across the south central United States, the 54-in. cylindrical pile was a new product to the company. Valley needed new forms to produce the piles, and that required a call to Hamilton Form. Early and frequent collabo- ration between Hamilton Form and Valley Prestress was essential in designing the form- work package for this project. The team had to determine the optimal bed length and think through set-up and stripping processes so the forms could be designed for the great- est production efficiencies. The forms were made in multiple seg- ments to allow the forms to be set up and broken down in stages. The piles have a 54-in. outside diameter with a 42-in. voided center. The two-piece outer form consists of a base, permanently installed in the bed, and a bolt-on removable top. Both sections have threaded coil rods bolted to the exterior of the form that act as void hold up and hold downs. The head- ers are also made in two sections, split hor- izontally. The collapsible interior void is hydraulically actuated. The overall bed is 520-ft. long. Outer forms were built in 50- ft. sections and the interior voids were built in various lengths to be assembled as needed for different product lengths. Once form drawings were completed, Hamilton Form built a prototype section of form to prove the geometry and test the hold-ups, void overlap and hydraulics. After testing, the forms went into produc- tion. Meanwhile, Valley Prestress was busy getting the bed ready. The ability to set-up and pour a 520-ft., multi-part bed is a major undertaking. After Valley prepared the bed and installed abutments, a staging area was built adja- cent to the bed. Included is a roller assem- bly, built to the same height of the product, so the product could be pulled straight out of the form. After the forms were installed, Valley began casting test piles. David Malaer, general manager at Val- ley Prestress, explains, "We did extensive research and planning, but once we started our initial casting, the real trial and error began. We refined our processes and dis- covered the timing of the production se- quence is absolutely critical." The process requires a three-day cycle. On day one, the lower headers are placed in the bed and strand is pulled to initial tension. Then bundled spirals are set at each header, and the voids are slid in be- tween the bottom form and the spiral. Next, the top headers are dropped into place, and the top strand is pulled to ini- tial tension. Afterward, the spirals are spread out, and strand is final tensioned. On the following day, the spirals are tied, and the top section of the form is bolted in place. Once the top form is in place, the coil rods in the top of the form are tightened to hold the void down to pre- vent it from becoming buoyant during the pour. The bed is now ready to be poured. The first pour fills the form just above the halfway point. Once the concrete is placed, the bottom coil rods are released. The con- crete holds the void in place at the bottom, while the top rods act as void hold downs during the final pour. Next, the form is filled and screeded at the top. Shortly thereafter, the top coil rods are backed out. When the concrete reaches preset, the top of the form is removed, and the product is kept hydrated with wet burlap. Continued on page 36 WWW.CONCRETEPRODUCTS.COM SEPTEMBER 2012 | 35