Published: Jan 1956
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Specifications for concrete structures are intended to insure that properties of the hardened concrete shall be suitable for the proposed service. It is not difficult to determine what is required in terms of strength, modulus of elasticity, permeability, and durability of the finished structure. But it is difficult, if not impossible, to specify and maintain exactly the properties of fresh concrete such as water-cement ratio, cement content, type and grading of aggregates, and the construction procedures of mixing, handling, placing, and curing that will result in hardened concrete of the desired properties. The problem is one of establishing standards for materials and procedures that will keep deviations in properties of the hardened concrete within predictable limits. The difficulty in establishing limits for these deviations is due to the many variables that are involved in the manufacture of concrete. The materials, particularly the aggregates, have wide ranges in physical and chemical properties and grading. Equipment for mixing, transporting, and placing concrete is seldom alike on different projects, and construction procedures for carrying out the different operations have not been standardized. Small wonder that concrete is not always a uniform product.
Manager, Portland Cement Assn., Research and Development Laboratories, Skokie, Ill.
Paper ID: STP39416S