INTRODUCTION 



Numerous experimental studies have been 

 performed at the Civil Engineering Laboratory 

 (CEL)" on the behavior of concrete structures under 

 hydrostatic loading [1-11]. These studies have 

 shown that concrete is well suited as a construction 

 material for pressure-resistant structures to depths of 

 3,000 feet. The empirical data were obtained from 

 test specimens subjected to relatively short-term 

 loading conditions where the longest loading-period 

 for any specimen was 42 days. This series of ocean 

 tests was conducted to supplement the earlier 

 research by providing data on concrete structures 

 subjected to in-situ deep-ocean conditions for periods 

 of up to 10 years. 



The objectives of the test program were to 

 obtain design information on time-dependent failure, 

 permeability, and durability of the concrete spheres. 

 Data on time-dependent failure will permit a rational 

 factor of safety to be applied to pressure-resistant 

 structures; data on seawater permeability of concrete 

 will allow predictions of the quantity of water to be 

 expected to penetrate to the structure's interior; and 

 data on the durability of plain and steel reinforced 

 concrete will determine such factors as strength 

 changes with time, chemical composition changes of 

 the concrete, and steel corrosion problems. 



TEST DESCRIPTION 



Eighteen, 66-inch-OD concrete spheres were 

 placed in the ocean at depths ranging from 1,840 to 

 5,075 feet (Table 1). This depth range corresponds to 

 a sustained pressure-to-short-term implosion pressure 



ratio, Ps/Pim-'^ °^ ^-^^ "^° ^•^^- '"^ ^^^ anticipated 

 that the spheres subjected to a Pj/Pim "^^^io of 0.70 or 

 greater would implode with time [8] ; therefore, the 

 six spheres at greatest depths were equipped with 

 clocks that would count days in periods up to three 

 years. If a sphere imploded, the clock would record 

 the day of failure. 



Permeability data will be gathered using the 

 following method: the spheres are buoyant by 

 approximately 1^000 pounds and are tethered 32 feet 

 off the seafloor by a 2-1/4-inch-diameter chain. As 

 seawater permeates the concrete, the weight of the 

 sphere will increase. The reduced buoyancy of the 

 sphere means less chain can be suspended off the sea- 

 floor, so the sphere moves closer to the seafloor. A 

 change in height of one chain link (2-1/4-inch chain) 

 corresponds to 0.5 cu ft of seawater which has 

 permeated to the hull interior. 



The permeability rate of seawater through 

 waterproofed and nonwaterproofed concrete will be 

 determined. Eight spheres were coated on the 

 exterior with a two-part phenolic coating; another 

 eight spheres remained uncoated. All sixteen of these 

 permeability specimens were of unreinforced 

 concrete. The remaining two spheres were reinforced 

 with conventional steel bars of 0.5-inch diameter. The 

 reinforcement was covered with 1 or 2.5 inches of 

 concrete. Also, one-half of the exterior of each sphere 

 was coated with the phenolic compound while the 

 other half remained uncoated. 



The durability of the concrete will be studied by 

 determining the changes in strength and chemical 

 composition with time. The concrete compressive 

 strengths will be obtained from core specimens drilled 

 from 14 X 18 x 18-inch blocks. Blocks are located 

 with the spheres in the deep ocean and on land. 



Formerly the Naval Civil Engineering Laboratory; now a detachment of the Naval Constmction 

 Battalion Center, Port Hueneme, California. 

 Numbers in brackets indicate references. 

 '^ The short-term implosion pressure, P;,^, is calculated by the following empirical equation |81 : 



P:„ = [5.02(t/D„) - 0.038] f; 



