INTRODUCTION 
Previous work (Ref 1) involved the feasibility of placing freshly 
mixed concrete at deep ocean depths. The Navy has an interest in such 
capability relative to building in-situ structures and foundations. The 
investigation (Ref 1) determined that the task would be feasible using a 
drillpipe suspended from a surface platform to convey the concrete by 
gravity force to the seafloor. Flow control would be maintained by 
frictional forces between the pipe and concrete. The technology appeared 
to be state-of-the-art for the hardware and ocean engineering systems, 
but tests were recommended on the concrete materials. 
This study pertains to one aspect of the concrete behavior -- its 
compressive strength after being placed on the seafloor and allowed to 
set and cure. The main question is: If freshly mixed concrete is 
placed on the seafloor for structural purposes, what will be the result- 
ing in-situ compressive strength? A test plan was formulated to deter- 
mine whether a long-term (up to 2 years) strength-change occurred because 
of the effect of the deep ocean environment on the concrete. 
TESTING PROGRAM 
The concrete placement procedure for deep depths should follow the 
basic method for that of tremie-placed concrete. This method has the 
end of a pipe submerged in the deposited concrete so that the mass of 
deposited concrete grows from within; in this manner, there is minimum 
mixing between seawater and concrete, and few cement fines wash away. 
For this testing program, freshly mixed concrete was placed in the 
ocean by confining the material in 6 x 12-inch (152 x 305-mm) cylindrical 
plastic molds. The concrete was exposed to the pressure environment and 
to the seawater by providing two 1/8-inch (3-mm) diam holes in the lids 
to the molds. The lids prevented the cement fines from washing away. 
The procedure simulated the tremie placement condition of freshly mixed 
concrete being exposed to seawater under hydrostatic pressure. 
Speed of concrete placement was another important consideration be- 
cause the concrete should be workable when it reaches the seafloor. It 
was conceivable that hydrostatic pressure could compact the concrete. 
For two principal reasons, namely, the quantity of specimens to be cast 
and cost constraints, the concrete test specimens were made ashore, 
transported immediately after casting to the oceanic site by helicopter, 
and allowed to freefall to the seafloor. Because of this approach, the 
individual specimens were confined within a framework that could be 
transported inside a military helicopter, and could freefall through 
water in a stable manner. Freefalling was risky because the seafloor 
has rock outcrops that could cause the framework to overturn; hence, it 
was necessary to use two frameworks to increase the odds of attaining an 
upright landing. 
