Durability Considerations for Concrete Water-Retaining Structures


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Title: Durability Considerations for Concrete Water-Retaining Structures

Author(s): Nihal Vitharana

Publication: Special Publication

Volume: 170


Appears on pages(s): 1379-1410

Keywords: Concretes; cracking (fracturing); durabilty; heat-of-hydration; loads (forces); shrinkage; stiffness; strains; temperature; thermal stresses.

Date: 7/1/1997

This paper presents the results of several studies carried out on the parameters affecting the durability and serviceability performance of concrete water-retaining structures. It has been identified that one of the main causes for the early deterioration of concrete water-retaining structures is the occurrence of strain-induced loadings arising from temperature changes, shrinkage, and swelling. However, a majority of the current design guidelines and recommendations are quite cursory in this regard. The evaluation of induced strains, as well as stresses generated by the restraining effects, is quite complex compared with the effort needed for much-familiar dead and live loads. It was shown that the strain-induced loadings are as significant as the hydrostatic loading. The inevitable cracking of concrete relaxes the strain-induced loadings and this aspect should be considered if economical and practical designs are to be achieved. Swelling of concrete, occurring after filling the reservoir, generates a differential strain gradient across the wall thickness. A comprehensive analysis method was developed to predict the wall structural behaviour from basic moisture transfer modeling. Creep of concrete would relax the induced stresses by about 50% generally. Concretes with low W/C have been introduced recently in order to achieve improved impermeability properties and strength parameters. An inherent property of low W/C concrete is the autogenous shrinkage taking place during hydration. When restrained, this could cause through-depth cracking, thus making the structures unserviceable.