Lightweight concrete slabs only 5-1/2 inches thick project 45 feet from the circular cores of the twin towers that comprise Marina City in Chicago. The 60-story structure climbed 588 feet in 1962 to become the world's tallest reinforced concrete building of its day. The first 20 floors of each tower are for parking, and here the slab is in the form of a continuous spiral. The upper 40 floors are residential, and a complex of shops and services rounds out the city-within-a-city scheme.
Among the construction methods and materials used at Marina City were the following: Two types of concrete (conventional concrete with a specified 28-day strength of 500 psi for the central service cores and double rings of all columns that support floor slabs, and expanded shale aggregate, 3/8-inch maximum size, in a mix that weighed about 100 pounds per cubic foot for the slabs); welded wire fabric sheets used in the slabs; plastic footed or tipped bolsters to support steel in the slabs (to prevent rust stains on lower surfaces over which plaster ceilings were to be applied); glass fiber reinforced plastic forms; and materials handling by conveyor.
Some of the practices considered innovative at Marina City have since become commonplace, or have evolved into much more sophisticated systems and equipment available today.