strength. However, this strength was still 

 15% less than companion concrete con- 

 tinuously fog-cured. 



3. Three spheres were retrieved from the 

 ocean where they had been exposed to a 

 preload of 50% of their ultimate strength 

 for 5.3 years. These preloaded spheres 

 were tested in the laboratory under 

 short-term loading and, in general, 

 behaved similarly to that of non-pre- 

 loaded spheres. Whether preloaded or 

 non-preloaded, the saturated (uncoated) 

 concrete spheres had a tendency to fail 

 at lower pressures than those of dry 

 (coated) concrete spheres. 



4. Three of the original eighteen spheres 

 have imploded in the ocean under long- 

 term loading. The remaining spheres 

 have withstood load levels of 0.3 to 0.8 

 of their predicted short-term strength. 



5. The permeability of concrete in 

 uncoated spheres has shown a decrease in 

 rate with time and, in several cases, the 

 permeation of seawater through the 

 concrete wall has stopped. Coated 

 (waterproofed) spheres remained dry on 

 the interior. 



6. X-ray diffraction analysis of the fog- 

 cured and ocean-cured concrete has 

 shown the 5.3-year ocean-cured concrete 

 - whether coated or uncoated - to be 

 essentially unchanged from the fog-cured 

 concrete. 



SUMMARY 



After 6A years in the ocean, the 

 long-term test on concrete spheres at 

 deep ocean depths has demonstrated 

 several important factors that will result 

 in design criteria for undersea concrete 

 structures. Those items are listed in the 

 Findings section above. To summarize: 



(1) the compressive strength of concrete 

 decreased slightly due to becoming 

 saturated with seawater, (2) the rate of 

 strength gain with time for concrete in 

 the deep ocean was slower than that for 

 concrete cured in a standard fog room, 

 (3) spheres exposed to a load 50% of 

 their short-term strength for 5.3 years 

 behaved in a manner similar to that of 

 spheres that were not exposed to a long- 

 term load, i^) twelve spheres are still in 

 the ocean and are withstanding pressure 

 loads that range from 1,840 to 4^875 feet 

 (560 to 1,^^86 m), (5) the permeability of 

 uncoated concrete was quite low, (6) if 

 complete watertightness is desired, a 

 waterproof coating was found to be 

 effective, and (7) the durability of 

 concrete in the deep ocean was found to 

 be excellent. 



The results from this study show 

 undersea concrete structures to behave 

 exceptionally well at deep ocean depths. 

 The strength, permeability, and 

 durability of the spheres are within or 

 exceed engineering acceptability limits. 

 Confidence in using concrete for 

 undersea structures is substantiated and 

 enhanced by the results of this ocean 

 test. The test is continuing, and addi- 

 tional data will be forthcoming. 



ACKNOWLEDGMENTS 



The authors wish to acknowledge the 

 able assistance of Mr. Phillip C. Zubiate 

 as the senior project technician for this 

 task from its beginning, and the support 

 and cooperation of the Navy's Submarine 

 Development Group One for its services 

 in conducting the submersible operations. 



REFERENCES 



1. Civil Engineering Laboratory. Techni- 

 cal Report R-805: Long-term deep ocean 



31^ 



