sections of lightweight concrete could be used than normal weight concrete 

 and permit additional space for prestress or reinforcing steel and allow 

 for improved impact and punching shear resistance. Highly stressed lo- 

 cations of the hull can be fabricated with thicker sections of lightweight 

 concrete and thus reduce the average stress. The inelastic behavior of 

 lightweight concrete can also aid in significant redistribution of stresses 

 in overstressed hull locations. 



An example of expanded shale lightweight concrete usage in an ocean 

 structure is given by the USS SELMA, a 7,500-ton vessel built in 1918. 

 The vessel is presently grounded on a beach in Galveston, Texas, and 

 reportedly the durability of the concrete and lack of steel corrosion are 

 outstanding f eatures .L 3 5 J 



Lightweight aggregate concretes have not been tested for their suit- 

 ability in pressure-resistant structures subjected to several hundred 

 feet of hydrostatic head. In particular, information is lacking on the 

 permeability of lightweight concrete subjected to such pressures. Only 

 limited information is available on seawater absorption of expanded shale 

 lightweight concrete; experimental results were inconclusive. L 36 J The effect 

 of partial and full saturation with seawater on compressive and tensile 

 strengths of lightweight concrete is not known. In summary, there is a 

 lack of knowledge of the engineering properties and behavior of lightweight 

 concrete for ocean structures. 



Antifouling Concrete . OTEC structures will experience marine bio- 

 fouling. For example, the North Sea structures in 100-foot water depths 

 show about 4 inches of vegetation and animal growth from the tide zone 

 to 30-foot depth after several years of operation. Below 30 feet, 4 inches 



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