for all degrees of compaction, although the very high
(143 tons). The energy required for the hydraulic pump
loading rate might not prove as effective as some slower
for a press of this magnitude would draw around 2 kw
means.
of electric power at maximum pressure. Roughly 20
blocks could be made in an hour for a maximum energy
cost of less than 2 kwh (7.2 mj). This is almost enough
CONCLUSIONS
energy to melt one of these bricks, or to increase the
water content of the total volume of snow to almost
In terms of the original thrust of the project--to
5%.
develop a low-energy method of producing high-
While snow with 5% moisture content would be an
strength compacted snow for construction purposes--
excellent material for conventional snow-compaction
the results reported here show that CFG ice is a strong-
methods, there are a number of problems with produc-
enough construction material for most paving
ing it in very cold areas:
applications, and more than strong enough for building
walls, shelters, and so forth.
Numerous techniques have been tested in Antarctica
Since the initial density of the bricks was in the ice
and in Greenland with very modest success. It
range, i.e., the bubbles were isolated, many problems
appears to be a formidable problem to achieve
are minimized, such as those associated with vapor
uniform distribution of the heat through the surface
movement, e.g., depth hoar, as well as with percolation
snow layer, and this results in very uneven strength
of salt water or other fluids. The material appears to be
of the compacted layer.
stable in a thermal gradient as well.
The very great amounts of heat required to overcome
The CFG ice produced in this study is interesting
the latent heat of fusion of ice to produce water vastly
for a number of reasons. First, the means of its
increase the energy cost of melting snow either to
compaction (using extremely high compaction
raise the moisture content of the snow cover or to
pressures) appears to have completed the sintering
produce bulk water for application as spray or steam.
process at the time of fabrication, as there is no
The energy cost goes far beyond that of warming
evidence of increasing strength, either compressive or
the snow, as the subsequent processing would
flexural, with time. Second, the very small grain size
involve numerous passes with rollers, planes, and
resulting from the high compaction pressures appears
similar equipment.
to be stable, at least in the conditions prevailing in this
Even under optimum conditions it is difficult to
study. In most cases the crystal sizes do not appear to
achieve a uniform compacted snow layer with a
density as high as 700 kg/m3, and the resulting
have changed appreciably even after 20 days. This
further supports the idea that the sintering process is
material is not as strong as natural ice, whose strength
complete at the time of fabrication. Third, the material
marks the lower bound of CFG ice.
is very strong and seems to be tough, although fracture
Since conventionally produced compacted snow is
toughness was not measured. The small grain size may
porous, it is still subject to such problems as depth
account for this, as crack propagation would be
hoar development, and is unsuitable for use in areas
inhibited both by this and by the small, uniformly dis-
where water infiltration, especially salt water, is
tributed bubbles.
likely.
We used a hydraulic press in this study to compact
the snow because it was convenient, available, and easy
LITERATURE CITED
to monitor. Other techniques may be used with equal
success, such as a lever arm, perhaps in conjunction
Abele, G., and A.J. Gow (1976) Compressibility
with a hydraulic press or a mobile roller assembly to
characteristics of compacted snow. U.S. Army Cold
produce a continuous sheet of compacted material.
Regions Research and Engineering Laboratory,
Equipment limitations may dictate the maximum
CRREL Report 76-21.
load applicable by hydraulic or mechanical apparatus.
Abele, G., R.O. Ramseier, and A.F. Wuori (1968)
Another means of achieving a great force is by drop-
Design criteria for snow runways. U.S. Army Cold
ping a dead weight from various heights. A 500-kg
Regions Research and Engineering Laboratory,
weight, for example, dropped from a height of 3 m
Technical Report 212.
will produce an impact load from about 25 up to nearly
Butkovich, T.R. (1962) Studies of the age hardening
100 tons, depending on sinkage. If the resulting brick
of processed snow. U.S. Army Cold Regions Research
has the same properties as one compressed to the same
and Engineering Laboratory, Research Report 99.
degree but over a longer time, this compaction method
Ebinuma, T., and N. Maeno (1984) Experimental
may prove to be the easiest and most practical, perhaps
14
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