INTRODUCTION 



The first application for lightweight concrete, in I9I9, was for a 

 concrete ship 434 feet long named the USS SELMA. During World Wars I 

 and II, hundreds of ships and barges were made of lightweight concrete. 

 More recently, normal weight concrete has found considerable application 

 in energy-related offshore structures, such as oil drilling and produc- 

 tion platforms. Proposals abound for other applications, such as sub- 

 merged oil production enclosures, seafloor fuel storage tanks, and even 

 liquefied natural gas transport ships. In any one of these applications, 

 a construction material lower in unit weight than normal weight concrete 

 would be beneficial to the designer in planning a structure of less 

 draft or higher payload capacity. 



An application with major economic implications for the United 

 States is related to future structures for ocean thermal energy conver- 

 sion (OTEC) . OTEC uses the temperature difference between the warm 

 surface water and the cold deep ocean water to evaporate and condense a 

 liquid for driving a turbine to generate electricity. Not only is a 

 massive floating platform required to support the hardware on the surface, 

 but an enormous cold water pipe that may be on the order of 60 feet in 

 diam and 2,000 feet long is also required. The pipe must be "flexible" 

 to reduce bending moments during periods of rough weather. Hence, it 

 would be helpful if the construction material had a low elastic modulus. 



Regular lightweight concrete is a candidate construction material 

 for OTEC. Compared to normal weight concrete, lightweight concrete 

 potentially can save weight of 40% while maintaining a compressive 

 strength of 5,000 psi and better. 



This study investigated a material that would also have a weight 

 saving of 40%; but possibly with a compressive strength greater than 

 that of regular lightweight concrete. This material, a lightweight 

 Portland cement concrete, used specially prepared aggregate. The special 

 aggregate was regular lightweight aggregate that had its void volume 

 filled with a polymeric material. 



There were several reasons for filling just the aggregate and not 

 the entire concrete material: 



1. The specific gravity of polymer is approximately equal to that 

 of seawater. Hence, aggregate filled with polymer would have approxi- 

 mately the same weight as seawater-saturated regular lightweight aggre- 

 gate. This means that the in-water unit weight of concrete saturated 

 from deep ocean exposure would be the same if polymer-filled aggregate 

 (PFA) or regular lightweight aggregate were used. 



