Title: Corrosion Fatigue in Concrete For Marine Applications
Author(s): P. D. Arthur, John C. Earl, and Trevor Hodgkiess
Publication: Symposium Paper
Appears on pages(s): 1-24
Keywords: beams (supports); bending; concretes; corrosion; cracking (fracturing); fatigue (materials); fatigue tests; marine
atmospheres; offshore structures;
concrete; sea water. prestressed concrete; reinforced
Structural concrete is widely used in marine environments, but a relatively recent development has been its use in structures such as oil production platforms, ships, wave energy devices etc., where fatigue loading can be significant. It is well known that the effect of a corrosive environment on structural steelwork is to reduce its fatigue life, and this paper describes work in progress to determine whether or not the same is true for structural concrete, both reinforced and prestressed. Reinforced and prestressed concrete beams are being tested in unidirectional bending, and in reverse bending, in jackets containing sea-water, at slow cycling rates (about 0.17 Hz)which approximate to sea-wave frequencies. The sea-water is pH and temperature controlled and is continuously circulated from a storage tank. Control specimens are tested at higher frequencies (3 to 5 Hz) and these show the expected reduction in fatigue endurance, compared withtests in air. However, the wave-frequency test results show that deposits are formed in the flexure cracks after 3 to 4 days of cyclic loading, and this has the effect of increasing, rather than decreasing, the fatigue lives of the beams - certainly when the bending is unidirectional. Under reverse bending this effect is not yet confirmed, although the crack-blocking is observed to take place. Electron-microscopy of the failure surface is being utilised to establish the mechanism by which corrosion fatigue failure occurs under these conditions.