The deep-ocean concrete, cured and tested at a pressure head of 
1,830 feet (560 m), had a compressive strength of 6,600 psi (45.5 MPa) 
at age 11 months; this strength represented a decrease of 13.4% compared 
with that of the fog-cured concrete at age 10.8 months. 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 
pressure to 1,830 feet (560 m), had compressive strengths of 6,520 psi 
(45 MPa) and 6,490 psi (4.48 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). This finding was the same as that found for the low-strength concrete. 
When compared, the compressive strength results for the low- and 
high-strength concretes showed the following: 
1. As the concrete cured in the fog room from ages 28 days to 10.8 
months, the strength increased 27.9% and 25.7% for the low- and high- 
strength concretes respectively. 
2. The seawater-tank-cured concrete had strengths essentially the 
same as that of the fog-cured concrete of equal age. The one exception 
was the high-strength concrete cured in the seawater tank for 10.2 
months; it showed an 8.8% decrease in strength compared with that of the 
fog-room-cured concrete. 
3. At 11.0 months, the deep-ocean, low-strength concrete had a 
strength essentially the same as that of the fog-cured, low-strength 
concrete, while the deep-ocean, high-strength concrete showed a strength 
decrease of 13.4% compared with that of the fog-cured, high-strength 
concrete. 
The relatively small decreases in compressive strength for the 
high-strength concrete may be explained by a physical phenomenon ob- 
served previously (Ref 2). Concrete saturated with water (pore volume 
either completely filled or essentially filled) has been found to have a 
compressive strength about 10% lower than that for concrete wherein pore 
volume is not saturated. The reason for this difference in strength may 
be due to pore-pressure buildup during uniaxial compressive loading for 
the saturated concrete. A small component of pore pressure acting in 
the radial direction will help form tensile microcracks that lower the 
ultimate compressive strength. Concrete that is not saturated would not 
experience the pore pressure buildup. 
It is known that pore water is consumed during cement hydration. 
The process is called self-desiccation because sufficient water is used 
during hydration to stop further hydration if an external source of 
water is not provided. The fog room, seawater tank, and ocean environment 
were external water sources; however, the fog-room environment was not 
as efficient in resupplying water to fill the voids as were the other 
two environments. At age 10.8 months, considerable hydration had occurred 
in the high-strength concrete, which means that most of the larger 
capillary voids had been filled with cement hydration products, prin- 
cipally calcium-silicate-hydrate "fibers" (Ref 3). The space between 
the fibers is the gel void volume through which water molecules move 
