INTRODUCTION 



In September 1971, a test program 

 was started on concrete spherical struc- 

 tures placed in the deep ocean for long- 

 term testing. This report is the second in 

 a series documenting the study; pre- 

 sented are the test results of the spheres 

 after 6.^ years in the ocean. The first 

 report (Ref 1) covered the fabrication, 

 ocean emplacement, and inspections up 

 to 1.3 years. Details of the test program 

 and the specimens are given in Refer- 

 ence 1. 



The technical objectives of the pro- 

 gram are to obtain data on time-depen- 

 dent failure, permeability^ and durability 

 of the concrete spherical structures. 

 These data can provide a technology base 

 from which engineering guidelines could 

 be written. Another important aspect of 

 the program was to expose the spheres to 

 real environmental conditions. The test 

 results will aid considerably in establish- 

 ing confidence and credibility for con- 

 crete as a deep-ocean construction 

 material. 



BACKGROUND 



Eighteen concrete spheres 66 inches 

 (1676 mm) in outside diameter and ^.12 

 inches (105 mm) in wall thickness were 

 placed in the ocean at depths varying 

 from 1,8^0 to 5,075 feet (560 to l,5'f7 

 m). Sixteen of the spheres were unrein- 

 forced concrete, eight of which were 

 coated on the exterior with a phenolic 

 compound to act as a waterproofing 

 agent; the other eight spheres were left 



uncoated. The remaining two spheres 

 were lightly reinforced with 0.5-inch (13- 

 mm) diameter steel bars. The reinforcing 

 bars had a concrete cover of 1 and 2.5 

 inches (25 and 63 mm). Half of the 

 exterior of each of these spheres was 

 coated with the waterproofing agent. 

 The reinforced spheres were to deter- 

 mine whether corrosion problems exist in 

 the deep ocean environment. 



The depth range for the spheres 

 corresponds to relative load levels of 

 from 0.36 to 0.83. The relative load 

 level, Ps /Pirn ' ^^ defined as the ratio of 

 sustained pressure to predicted short- 

 term implosion pressure. 



Time-dependent failure was expec- 

 ted for six of the spheres subjected to 

 the highest load levels; therefore, those 

 spheres were equipped with clock mech- 

 anisms to record the day of implosion. If 

 other specimens were to implode, the 

 yearly inspections would discover the 

 failed specimens. 



Permeability data were gathered 

 during inspections. The spheres, which 

 were approximately 1,000 pounds {^50 

 kg) buoyant, were tethered 30 feet (10 

 m) off the seafloor by a 2.25-inch {57- 

 mm) diameter chain. As seawater was 

 absorbed by and permeated through the 

 concrete, the sphere weight increased. 

 The reduced buoyancy of the sphere 

 meant that less chain was suspended off 

 the seafloor. Therefore, change of one 

 chain link corresponded to 0.50 cu ft (1^ 

 liters) of seawater being taken on by the 

 sphere. 



The concrete mix design was Type II 

 Portland cement, a water-to-cement 

 ratio of 0.^1, a sand-to- cement ratio of 



