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Good concrete must embody adequate workability, strength, and durability. The most important of these is durability. It is futile to provide ease of placement and an excess of load-carrying capacity if the structure does not remain functional and attractive for a reasonable period. Many factors contribute to concrete's ability to endure: the quality of materials, the proportions, the mechanics of mixing and placement, and the ambient conditions during construction and throughout the life of the structure. An important element is the quality of the aggregates—their soundness and freedom from deleterious substances. It is difficult to distinguish sharply between measurements which evaluate the soundness of an aggregate and those which identify deleterious substances. Soundness is the more general term, usually considered to be an attribute of the aggregate as a whole. Attempts to measure that property involve representative samples tested in such a way as to predict over-all performance level. In the case of deleterious substances, attention is focused on the individual particles or contaminants that may be harmful to concrete.
Bloem, D. L.
Director of engineering, Nat. Sand and Gravel Assn. and Nat. Heady Mixed Concrete Assn., Silver Spring, Md.