to a uniaxial compression test* to failure. One of the three specimens 
was instrumented with a compressometer-extensometer (ASTM C469), except 
that linear position transducers, adapted for underwater application, 
were used to measure displacements instead of dial gages. 
2. Six specimens each were tested under uniaxial compression while 
at a pressure head of 6 feet (2 m). None of these specimens was instru- 
mented. 
3. Six specimens each were tested under uniaxial compression while 
at a pressure head of 6 feet (2 m) after the specimens had been exposed 
to three rapid cycles of pressure to 1,830 feet (560 m) at a rate of 600 
ft/min (3 m/s). None of these specimens was instrumented. 
A total of 24 control specimens were tested using the same compres- 
sion testers as the deep-ocean concrete specimens. The fog-cured speci- 
mens were tested in the laboratory environment, while the seawater-tank 
specimens were tested under a pressure head of 6 feet (2 m). One-third 
of all these specimens were instrumented with the compressometer- 
extensometer. 
RESULTS AND DISCUSSION 
Compressive Strength 
Low-Strength Concrete. Table 1 shows that there was no significant 
change in strength between the fog-room cured and seawater-tank-cured 
concrete. The fog-room concrete had compressive strengths of 3,300 psi 
(22.8 MPa) at 28 days and 4,220 psi (29.1 MPa) at 10.8 months, an increase 
of 27.9%, while the seawater-tank concrete had compressive strengths of 
3,400 psi (23.4 MPa) at 28 days and 4,220 psi (29.1 MPa) at 10.2 months. 
The deep-ocean concrete, cured and tested at a pressure head of 1,830 
feet (560 m), had a compressive strength of 4,090 psi (28.2 MPa) at an 
age of 11 months. This strength was essentially the same as that for 
the 10.8-month fog-cured concrete; the decrease of 3.1% was not statis- 
tically significant. 
The deep-ocean concrete tested at a pressure head of 6 feet (2 m), 
and at a pressure head of 6 feet (2 m) after being subjected to three 
rapid cycles of hydrostatic pressure corresponding to 1,830 feet (560 
m), had compressive strengths of 4,320 psi (29.8 MPa) and 4,070 psi 
(28.1 MPa) respectively. These specimens did not show a statistically 
significant change in strength compared with that of the deep-ocean 
concrete tested at a pressure head of 1,830 feet (560 m). 
High-Strength Concrete. Table 2 shows there was no statistically 
significant change in strength between the fog-room-cured and seawater- 
tank-cured concrete at the age of 28 days, but at about age 10.5 months 
the seawater-tank-cured concrete showed a decrease in strength of 8.8% 
compared with that of the fog-room-cured concrete. The fog room concrete 
had a compressive strength of 6,060 psi (41.8 MPa) at age 28 days and 
7,620 psi (52.6 MPa) at age 10.8 months, an increase of 25.7%. 
*This test was not a triaxial compression test because no confining 
stress was imposed by the environmental pressure. The internal pore 
pressure of the specimen was in equilibrium with the external pressure. 
4 
