concrete strength is dependent on the degree of saturation and that 6- 

 inch-diameter , 12-inch—long cylinders under a pressure head of 500 feet 

 were not completely saturated after two months. Also, it was observed 

 that compressive strength of partly saturated concrete under hydrostatic 

 pressure showed small increases in uniaxial strength but that completely 

 saturated concrete showed strength decreases of 10% or more com- 

 pared to fog-cured concrete. 



The lack of knowledge about the behavior of saturated concrete is 

 an outstanding deficiency in the state-of-the-art. The pressure- 

 resistant hull is a highly stressed, critical component of OTEC and the 

 behavior of the construction material must be known. 



Lightweight Concrete . Structural lightweight concrete can be readily 

 produced with compressive strengths of 5,000 psi, and from some lightweight 

 aggregates, strengths of 6,000 psi. Lightweight reinforced concrete sat- 

 urated with seawater has a unit weight in the range of 115 to 125 pcf in 

 air and thus less than 60 pcf submerged. This represents an in-air weight 

 saving of 20% and a submerged weight saving of 30 to 35% or 

 more compared to normal weight reinforced concrete which, when saturated, 

 has a unit weight of about 155 pcf in air and 90 pcf when submerged. 

 Lightweight, as compared to normal weight, concrete has a lower modulus 

 of elasticity (about 60 to 75%) and, on the average, somewhat 

 greater creep and shrinkage. L J 



Aside from the obvious advantages of lower weight, which could greatly 

 affect the design of the cold water pipe and which might be critical in 

 being able to produce a structure of sufficient buoyancy, lightweight 

 concrete can be used in other ways. For equal weight structures, thicker 



18 



