very slowly. It is probable that the fog-cured concrete was not sat- 
urated because of the low permeability of the cement paste. Given addi- 
tional time (more years), the concrete could become saturated in the fog 
room (Ref 2). However, at age 10.8 months, the fog-cured concrete may 
not have been saturated. The deep ocean concrete was saturated and 
showed 13.4% less strength than that shown by the fog-cured concrete. 
Also, if the seawater-tank-concrete was saturated, its lower strength of 
8.8% could be explained by this phenomenon. 
The above discussion to explain strength differences does not apply 
to the low-strength concrete because, at the age of 10 to 11 months, 
strength differences did not exist. The high water/cement ratio of 0.66 
for this mix indicates that capillary voids would always exist. The 
capillary volume, formed by the original mixing water, was so large that 
gel fibers could not fill all the space; hence, permeability of water 
through the paste was considerably easier. It is possible that the 
saturated low-strength concretes did not develop pore pressure buildup 
during compressive testing because the capillary voids vented the pressure. 
Hence, the saturated concretes (seawater-tank and deep-ocean) behaved 
similarly to that of the unsaturated fog-room concrete. 
4. The deep-ocean concretes, both low- and high-strength, tested 
at a pressure head of 6 feet (2 m), showed strengths essentially the 
same as that for the deep-ocean concrete tested at 1,830 feet (560 m). 
This result implies that the concretes were saturated with water and in 
equilibrium with the external environment. When this case exists, 
high-pressure heads have no influence on the concrete strengths. 
5. The deep-ocean concretes, both low- and high-strength, tested 
at a pressure head of 6 feet (2 m) after being subjected to three rapid 
cycles of pressure head to 1,830 feet (560 m), showed strengths essen- 
tially the same as that of the deep-ocean concrete tested at 1,830 feet 
(560 m). The pressure cycles were imposed on the specimens to determine 
whether the pore structure was disrupted by any of the pressure cycling 
that occurred for the deep-ocean concrete. The results indicated that 
the pressure cycling rate of 600 ft/min (3 m/s) was not harmful, so it 
is likely that the cycling rate of 60 ft/min (0.3 m/s) when coming out 
of the ocean was also not harmful. 
The difference in pore pressure build-up between rapid pressure 
cycling and uniaxial loading is difficult to determine. For the rapid 
pressure cycling of 600 ft/min, the pore pressure changed at a rate of 
4.4 psi/sec (30 KPa/sec) (calculated as 1 psi/2.25 ft x 1 min/60 sec x 
600 ft/min). The maximum rate of pore pressure build-up within the 
concrete tested under uniaxial loading would be for the case where all 
the water was trapped within the concrete. The uniaxial loading rate 
was 50 psi/sec (345 KPa/sec) which would be the pore pressure build-up 
rate. This rate is 11 times greater than that from the rapid pressure 
cycling. However, it is known that all the pore water was not trapped 
within the concrete during uniaxial test. Beads of water formed on the 
exterior surface as the concrete was loaded uniaxially, so the magnitude 
of actual pore pressure build-up was unknown, but ranged between 0 and 
50 psi/sec (0 and 345 KPa/sec). 
