Introduction

Although there has been a large research effort into the behaviour of structural concrete in the marine environment during the past two or three decades, comparatively little attention has been given to the direct effect of water pressurisation on concrete strength, particularly at ocean-depth pressures. The most notable exception was the pioneering research of Haynes, at the Naval Centre in California, who principally studied the performance of large hollow concrete spheres, but also reported a limited number of tests on conventional solid specimens[1], noting a significant loss of compressive strength at a water pressure equivalent to submersion at 6000 metres depth. In contrast, it is generally accepted that active confinement applied mechanically to concrete, for example by steel prestressing, causes a considerable strength increase. The loss of compressive strength from water pressurisation observed by Haynes is therefore anomalous.

The main purpose of the investigation described here was to confirm and to quantify the compressive strength loss of concrete under high water pressure. In addition, tests were carried out on plain concrete beams to determine the degree of flexural strength loss from water pressurisation. Finally, a range of tests was carried out to find the reason for the loss of strength and to determine whether strength loss also occurs at lower water pressures. All concrete specimens tested in this study were stored continuously in water from casting until the time of test.