During the past few years the Detroit Metropolitan Wayne County Airport (DTW) has undergone many changes. Its transformation includes dramatic aesthetic improvements and the addition of a new terminal, a sixth runway, a south entrance road, a luxury class Westin Hotel, and a new parking garage—one of the largest in the world.
Started in the spring of 2004, work on the McNamara Terminal included general building improvements and the addition of 25 new gates, which were completed in 2005. The remainder of the Phase II project, including exterior paving, was finished in 2006.
This was no small project. The McNamara Terminal/Northwest World Gateway handles 80,000 passengers each day. The main Concourse A, where 64 of the 97 gates are located, consists of two, long wings laid end-to-end to create a nearly one-mile-long expanse of domestic and international jet gates.
The exterior portion of this expansion for Northwest Airlines included the use of slag cement in 80,000 square yards of concrete pavement around concourses B and C. Thickness of the pavement varies from 9 inches to 17 inches and includes some reinforced concrete. Because the majority of the work was around the terminals, it was difficult to pave large segments and therefore concrete pours were done at very low production rates.
Alkali-silica reaction (ASR) was a significant concern on this project because the that local fine aggregates are ASR-susceptible. Slag cement was the material of choice to mitigate the ASR, as it reduces the alkalis available for reaction in the concrete mixture, and lowers concrete permeability thus reducing the pore liquid that reacts with the aggregate. The mix chosen was was a Michigan DOT design with 35 percent slag cement. Another benefit of adding slag cement to the mixture was that it made the concrete easier to place and consolidate, and in warmer conditions slag cement extends concrete working time and helps keep mixture temperatures acceptable for paving.
Concrete with slag cement also produces a smoother pavement finish than a mix design containing 100 percent portland cement. This helps provide an improved ride for large jets and less wear and tear on service vehicles.
The Metro Airport Expansion pavement received Slag Cement Association’s 2006 Award for Best Use in the Durability category, for allowing the airport to construct a long-life pavement using local aggregates susceptible to ASR.