LONG-TERM, DEEP-OCEAN TEST OF CONCRETE SPHERICAL STRUCTURES-RESULTS AFTER 13 YEARS,
 Technical Report R-915, Naval Civil Engineering laboratory, Port Hueneme, CA, by R. D. Rail and R. L. Wendt, July 1985, 60 pages.

In 1971, a long-term, deep-ocean test was started on 18 pressure-resistant, hollow concrete spheres, 66 inches in outside diameter by 4.12 inches in wall thickness. The spheres were placed in the ocean near the seafloor at depths from 1,840 to 5,075 feet. over a 13-year period, annual inspections of the spheres using submersibles have provided data on time-dependent failure and reliability. After 5.3 years of exposure, three spheres were retrieved from the ocean for laboratory testing, and after 10. 5 years two more spheres were retrieved and tested. This report is the third report in a series describing and summarizing the findings from the ocean and laboratory tests. Data on concrete compressive strength pin, short-term implosion strength of the retrieved spheres, and permeability and durability of the concrete were obtained. The data have shown that concrete exhibits good behavior for ocean applications. High quality, well-cured concrete can be expected to gain and maintain strength when submerged in seawater under high pressure. Concrete is a durable material in the deep ocean; neither deterioration of the concrete matrix nor corrosion of reinforcing steel are problems, even though the concrete becomes saturated with seawater. Uncoated concrete has a very low rate of permeation of seawater through the concrete and even this small flow can be prevented by a waterproofing coating.

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