Page:America's Highways 1776–1976.djvu/469

 Additives for concrete that controlled the set for better workability and that produced more durable structures were being further developed. Even so, concrete bridge decks were beginning to show signs of early deterioration, caused by salt used as a de-icing agent penetrating the concrete and destroying the reinforcing steel. This brought about specialized construction methods for the protection of bridge decks, such as the use of epoxy coated or galvanized reinforcing steel and waterproof mastics or membranes.

During the years from 1967–1974, highway builders were finding an increasing scarcity of key highway construction materials, such as cement, steel, asphalt, and paint, which accelerated the search for alternate materials. Gasoline and diesel oil for the big rigs also became scarce, especially during the oil embargo late in 1973 and early 1974. The use of some waste materials in highway construction helped stretch existing supplies somewhat. For example, some States started using fly ash as a substitute for some of the cement in concrete mixes. Some experimented with rubber from old automobile tires to modify asphalt in hot mixes.

Now the United States has become a Nation bound together by an extensive ribbon of efficient well-maintained, quality streets and highways. Where once the horse and wagon slowly plowed through muddy roadways, millions of cars and trucks swiftly carry people, goods, and services to every corner of this country, impacting the social and economic wellbeing of every community. The ability to steadily obtain more production and an improved quality of construction and maintenance of this Nation’s streets and highways while still preserving a reasonably level cost is due to the combination of the many factors of the construction and maintenance system as it has developed. Some of these factors, which have been discussed, are the competitive bidding mechanism, the improved managerial methods, a dependable public financing, the advancing technology, and the motive force of the State and Federal Governments in desiring to meet the needs of the Nation and her people.

However, though the capability and motivation were present, the success of this effort required the excellent cooperative spirit that existed among the Federal Highway Administration and its predecessors, the State highway departments, and the industry associations. Without this partnership, there would not be the sound construction industry or the effective highway network that we have today.

Hanging a girder during construction of a three-level interchange in Dallas, Tex. 463