Underwater Fatigue Performance of Structural Lightweight Concrete

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Title: Underwater Fatigue Performance of Structural Lightweight Concrete

Author(s): V. Ramakrishnan, T. W. Bremner, and v. M. Malhotra

Publication: Special Publication

Volume: 145

Issue:

Appears on pages(s): 947-966

Keywords: compressive strength; fatigue (materials); flexural strength; lightweight aggregates; lightweight concretes; offshore structures; prisms; rupture; shales; stresses; underwater testing; Structural Research

Date: 5/1/1994

Abstract:
High-strength lightweight concrete is a promising material with many advantages over normal weight concrete in the construction of offshore structures that are submerged underwater for most of the time. In these structures, which are subjected to dynamic loading, the flexural fatigue strength and endurance limit of concrete submerged in water are important design parameters because these structures are frequently designed on the basis of fatigue loading. Presents the results of an experimental investigation to determine the flexural fatigue strength of lightweight concretes made using expanded shale aggregates. Six different concretes were investigated in this study. A total of 120 prisms (20 prisms of 76 x 102 x 406 mm, in size for each concrete) were tested in flexural fatigue loading of 20 cycles per sec (Hz) when they were submerged in water. The prisms that survived 2 million cycles of fatigue loading were tested in static flexure to demonstrate their residual strength (modulus of rupture). The test results are compared with the results of similar concretes tested in air in an earlier investigation. The static flexural strength (modulus of rupture) and the flexural fatigue strength were higher for the specimens tested underwater compared to similar specimens tested in air. In general, there was no reduction in the endurance limit (the ratio of the fatigue strength to the modulus of rupture) for the lightweight concretes when they were submerged in water. There was an increase in the residual static flexural strength for the prisms previously subjected to 2 million cycles of fatigue stress underwater.