Dallas/Fort Worth International Airport's seventh runway, 8,500 feet long and 150 feet wide, will soon meet demanding construction standards for smoothness. The 40-million dollar project requires 425,000 square yards of portland-cement-concrete pavement set on 440,000 square yards of lean-concrete base. The paving contractor, Granite Construction, is using three machines to facilitate placement of both the runway and the lean-concrete base - a four-track slipform paver, a custom-built belt placer, and a rubber-tired material transfer/placer.
For runway construction, the 165,000-pound slipform paver is working at a 37.5-foot width to place a superstiff concrete mix. This is allowing Granite to place the slab in four passes. Equipped with 40 vibrators, the slipform paver is effectively consolidating the high volume of stiff concrete. A hybrid belt placer that Granite assembled using two four-track placer/spreaders is perhaps aiding productivity even more. This customized placer can deliver concrete from both sides of the slab concurrently. Granite doesn't let the placer get more than 60 feet ahead of the paver, so the freshly placed concrete doesn't begin to set and become impossible to slipform. To help ensure accurate slab placement, the contractor is guiding the paver with two string lines, one on each side of the machine.