Properties of Concrete and Their Influence on Prestress Design

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Title: Properties of Concrete and Their Influence on Prestress Design

Author(s): Raymond E. Davis and G. E. Troxell

Publication: Journal Proceedings

Volume: 50

Issue: 1

Appears on pages(s): 381-391

Keywords: no keywords

Date: 1/1/1954

Abstract:
Of the various properties of concrete that have to be taken into consideration in prestre,ss design, there are three that merit special attention: (1) the necessity. for uniformity of quality of concrete throughout a prestressed member, (2) the desirability of employing a concrete for which the drying shrinkage will be low, and (3) the desirability of employing a concrete for which the creep under the action of prestress will be low. Factors which influence the degree of uniformity and magnitude of drying shrinkage and creep are discussed and suggestions made concerning the use of materials and practices which may be expected to lead to most favorable results. To secure uniformity, there is required a concrete mix that is more than ordinarily plastic and sticky, and which when vibrated will flow readily into place without segregation and bleeding. Close job control is required with respect to grading of materials, batching, USC of admixtures, mixing, trans-porting, and placing. Other things being equal, within the ordinary range of richnesses of mix, drying shrinkage of concrete is nearly proportional to the quantity of mixing water employed; creep is proportional to the quantity of hardened cement paste and the water-cement ratio. To keep these effects at a minimum, it is , desirable that the paste content be the minimum and the water-cement ratio be the minimum which will produce,a fresh concrete of the desired properties and a hardened concrete of the desired strength. Additional factors affecting shrinkage and creep include cement composition; grading, maximum size, and character of aggregates; admixtures (affecting uniformity as well as shrinkage); size of prestressed members; and others.