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    Ready-Mixed Concrete

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    Ready-mixed concrete—defined as concrete sold as a finished product ready for use in a plastic and unhardened state—represents the largest category of portland cement concrete used in the United States. Approximately 150,000,000 cubic yards were produced in 1964. That accounts for about 60 per cent of all the cement sold in this country. The growth of the industry has been very rapid. In 1930 there were fewer than 200 companies producing not more than 5,000,000 cubic yards. The 150,000,000 cubic yards for 1964 come from some 5,000 to 6,000 companies. There has been a similar dramatic development in equipment to produce ready-mixed concrete. Prior to about 1930, the typical central mixer had a capacity of 1 to 112 cubic yards, although there were a few of 3 cubic yard capacity, and a few plants had more than one mixer. The concrete was transported in dump trucks, in special watertight open bodies, and, to a lesser extent, in the then recently developed agitators. The open trucks commonly had capacities of 1 to 2 cubic yards, and the agitators were only a little larger—about 2 to 3 cubic yards. Today central mixers of 6 cubic yard capacity and larger are the general rule. Many have capacities of 9 to 10 cubic yards and more. The predominant current practice is to use a truck mixer for the delivery of the centrally mixed concrete. Open bodies or agitators not suitable as mixers are used principally under special circumstances—generally for a particular job.

    Author Information:

    Walker, Stanton
    Director of engineering emeritus, Nat. Sand and Gravel Assn. and Nat. Ready Mixed Concrete Assn., Silver Spring, Md.

    Committee/Subcommittee: C09.40

    DOI: 10.1520/STP49888S