A nonstandard test was conducted to obtain an indication of the 
duration of workability for the concrete mixtures. A handful of freshly 
mixed concrete was manipulated manually to determine whether the concrete 
retained plasticity or crumbled. The low-strength mix crumbled 5.5 
hours after the start of mixing, and the high-strength concrete, after 
4.0 hours. 
COMPRESSIVE TESTING PROCEDURE 
Of 240 6 x 12-inch (152 x 305-mm) concrete test cylinders, 120 
were low-strength concrete and the other 120 were high-strength concrete. 
Thirty-six low-strength and thirty-six high-strength specimens were 
placed in the Pacific Ocean at 1,830 feet (560 m) (18 low-strength and 
18-high strength specimens in each framework). The temperature at this 
depth is about 42°F (6°C). The remaining 168 specimens were divided 
equally so that 84 were cured in a fog room at 73°F (23°C) and 84 cured 
in a tank of continuously circulating sea water at an average tempera- 
ture of 66°F (19°C). 
At age 28 days, six control specimens from both the fog room and 
the seawater tank were tested in compression; no deep-ocean specimens 
were tested at this age. At an age of about 3 months, an attempt was 
made to retrieve the deep-ocean specimens, but the framework outfitted 
for surface recovery equipment did not function. Therefore, specimens 
were not tested at this age. At an age of about 10 months, a manned 
submersible operation was conducted, and one framework was recovered 
(Figure 1). 
The specimens were transported to CEL and placed in seawater. 
Since the tops of the specimens were not level, approximately 1 inch (25 
mm) of concrete was cut from the top of each specimen after the plastic 
molds were removed. At this stage all 36 specimens were placed in 
seawater inside pressure vessels in CEL's Deep Ocean Laboratory and 
subjected to a hydrostatic head of 1,830 feet (560 m). The specimens 
were at atmospheric pressure for about 43 hours. 
Several pressure vessels were used so that when the pressure was 
relieved in one vessel all of those specimens could be subsequently 
tested. In this manner, the deep-ocean specimens underwent two pressure 
cycles before testing: from the seafloor to the atmosphere, in the 
pressure vessel for temporary storage, out of the pressure vessel for 
preparation for compressive load testing and back into the pressure ves- 
sel for test. During removal from the ocean, the depressurization rate 
was about 60 ft/min (0.3 m/s). This rate was used in pressurizing and 
depressurizing the pressure vessels. 
The 18 specimens for each low- and high-strength concrete cured in 
the ocean were tested as follows: 
1. Six specimens each were tested in compression while at a simu- 
lated deep-ocean depth of 1,830 feet (560 m). Using three portable 
compression testers, three specimens at a time were subjected to the 
deep-ocean environment (Figure 2), allowed to achieve equilibrium with 
the environment for 3 hours (i.e., allowed the pore pressure within the 
concrete to become equal to the external pressure), and then subjected 
