The High Five interchange will use 500,000 yd. of concrete for structures, drill shafts, walls, and paving. To accelerate workflow, TxDOT specified the use of the concrete maturity method (note box), an ACI and ASTM standard for estimating concrete strength based on variables such as time from placement and temperature of the mix. The method is being used for cast-in-place conditions and site-fabricated precast. Zachry has set up two batch plants, one transit and one central, at the interchange site to accommodate an irregular pour schedule for foundations, piers and pavement, and supply a precasting operation that will yield 623 box girder segments between March 2002 and January 2004. Job specifications allowed a uniform ternary blend mix, with a 50/30/20 proportion of cement, slag and fly ash supplied, respectively, by TXI, Lone Star and Boral Materials. Zachry has equipped the casting and staging yard with 10 paving mixers and six dump trucks.

The original Dallas High Five plan called for TxDOT U-shaped tub girders on second- and third-level structures, and cast-in-place box girders for the flyover ramps creating the fourth and fifth levels. Project Design engineer HNTB/Dallas decided to use the cast-in-place specification because building a casting yard on site, while nearby candidate properties presented access seemed doubtful, and the available properties nearby presented access and handling limitations. As the project neared funding, TxDOT secured a lease on a vacant, 30-acre lot along the interchange site's southeast corner. Zachry teamed up with an Italian company, Rizzani deEccher, to change the design to segmental precast using Parsons Bridge & Tunnel, Tallahassee, Fla., for construction engineering. A Rizzani subsidiary, Deal Srl, proposed furnishing 1) a segment erector, a 100-ton device measuring 97 ∞ 38 ∞ 37 ft.; and, 2) three forms to cast segments sized in 8- or 10-ft. lengths, 19- or 38-ft. widths, 7.5- to 15-ft. heights, and weights of 50 to 70 tons.

The $1 million segment erector can lift the heaviest members from a staging area on the space-restricted site to the top of the pier at the rate of 30 feet per minute. Once a segment is on the top, the erector can travel from end to end of the cantilevered pier at a rate of 0.45 mph. The ability to lift a segment from either end of the cantilever and travel with it to the point of placement is unique to the erector. Using the erector has minimized the impact on traffic traveling underneath the construction area and allowed the change from cast-in-place to precast segments.

The Zachry-RdE joint venture will continue segment fabrication for the flyover ramps through next January. Meanwhile, San Antonio-based Bexar Concrete is producing 123,000 lineal feet of tub girders and 2.5 million sq. ft. of precast decking. Extensive precast wall panels and rail/coping components are being supplied from a plant in Hillsboro, Texas, under a contract with Foster Geotechnical.