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Concrete Bridges Concrete is the most-used construction material for bridges in the United States, and indeed in the world. The application of prestressing to bridges has grown rapidly and steadily, beginning in 1949 with high-strength steel wires in the Walnut Lane Bridge in Philadelphia, Pennsylvania. According to the Federal Highway Administration’s 1994 National Bridge Inventory data, from 1950 to the early 1990s, prestressed concrete bridges have gone from being virtually nonexistent to representing over 50 percent of all bridges built in the United States. Prestressing has also played an important role in extending the span capability of concrete bridges. By the late 1990s, spliced-girder spans reached a record 100 m (330 ft). Construction of segmental concrete bridges began in the United States in 1974.Curretly, close to 200 segmental concrete bridges have been built or are under construction, with spans up to 240 m (800 ft). Late in the 1970s, cable-stayed construction raised the bar for concrete bridges. By 1982, the Sunshine Skyway Bridge in Tampa, Florida, had set a new record for concrete bridges, with a main span of 365 m (1,200 ft). The next year, the Dames Point Bridge in Jacksonville, Florida, extended the record to 400 m (1,300 ft). HIGH-PERFORMANCE CONCRETE Compressive Strength For many years the design of precast prestressed concrete girders was based on concrete compressive strengths of 34 to 41 MPa (5,000 to 6,000 psi). This strength level served the industry well and provided the basis for establishing the prestressed concrete bridge industry in the United States. In the 1990s the industry began to utilize higher concrete compressive strengths in design, and at the start of the new millennium the industry is poised to accept the use of concrete compressive strengths up to 70 MPa (10,000 psi). For the future, the industry needs to seek ways to effectively utilize even higher concrete compressive strengths. The ready-mixed concrete industr