TM 5-852-4/AFM 88-19, Chap. 4
of the permafrost table which will exist after
analysis, and detailed mix-design studies are justified.
23
construction . Protective coatings which are brittle or
Frost action is less detrimental in areas which are so
which have linear shrinkage coefficients widely different
cold that materials remain frozen throughout the winter
from steel should be avoided.
than in warmer areas where frequent freeze-thaw cycles
c. Concrete and masonry. Portland cement
occur during the winter months.
concrete is an extremely useful material in the cold
(3) Tests performed by Monfore and
173
Lentz to determine the suitability of concrete for use in
regions.
Gravel and sand deposits and/or rock
underground storage structures for liquefied natural gas
exposures are usually readily available (though this is not
ascertained the characteristics of concrete in very cold
necessarily so).
With proper processing of these
temperatures down to -250 F (-157 C). Sand and
deposits and with suitable water available, only the
gravel mixes with three different cement contents and
cement and air entraining component has to be
one using expanded shale for aggregate were used. All
imported. Good concrete is durable:' and presents no
samples employed air entrainment in amounts varying
fire hazard. Because concrete needs to be warm during
from 5.3 to 7.8 percent. Test temperatures ranged from
mixing, placement and curing and because it generates
+ 75 to -250 F ( + 24 to -157 C). Proceeding down
heat internally for a considerable time, difficulties arise
through the temperature range, Young's modulus
when concrete is to be placed on or near Permafrost
14
increased approximately 50 percent for the saturated
samples, increased only 8 percent for those stored at 50
and its effects.)
percent relative humidity, and remained the same for the
(1) Concrete which is exposed to freezing
oven-dried.
Poisson's ration remained essentially
at very early periods may be damaged sufficiently to
unchanged throughout the temperature range at
seriously lower the strength and durability which
approximately 0.22. Over the 325 F (181 C) range, the
otherwise will be attainable. It is necessary, therefore, in
all cases to carefully protect concrete against freezing for
contraction of the samples was in the neighborhood of
-3
the first 48 hours and for such additional time as may be
1.4 x 10 in./in. Compression tests showed an increase
needed to meet minimum strength and curing criteria
in strength with an increase in the cement factor.
(para 6-4). Beyond this critical point, concrete hardens
Strength curves for various cement contents exhibited
very slowly at low temperatures, and below freezing
similar trends with temperature (fig. 2-23a). The
there is almost no increase in strength or hardness.
compressive strength of the samples with 5.5 bags/yd'
Concrete which has been kept at a low temperature for a
cement content showed little change from + 75 to + 40
F (+24 to + 4 C) at about 5000 psi. At +40F (+4C) an
period may resume hydration and strength gain at an
increased rate when favorable conditions are provided.
upward trend started, reaching a maximum of
If subjected to large drops in temperature at early
approximately 18,000 psi at -150F (-101 C). This
periods cracking may occur, particularly if some degree
overall increase in strength is due to moisture within the
of restraint exists against shrinkage. However, concrete
samples (fig. 2-23b). Tests on oven-dry samples
also shrinks and cracks if cured quickly by too much
showed an increase in strength of 20 percent from +75
heat.
Some research has been done to develop
to -150F (-101 C), 50 percent moist samples gained
concretes which will set and gain strength at below
only slightly more, while 100 percent moist samples
freezing temperatures". However, these depend on use
increased by 240 percent.
of salt admixtures. They have not yet been tried in actual
(4) Precast and prestressed reinforced
construction and the possible effects of the salts on long
concrete may be used for foundations as well as
range strength and durability are unknown. They should
structures in arctic regions but special care must be
be used with caution in reinforced or pre-stressed
taken where frost heave, settlement or freeze-thaw
concrete because of corrosion hazard and never in the
under moist conditions may occur. Heave may, for
presence of zinc or aluminum.
example, produce tensile stresses and cracking in
(2) Freezing and thawing cycles in
reinforced concrete bearing piles.
While precast
completely cured good quality air-entrained concrete are
reinforced concrete sectional buildings have been used
not generally harmful but if the concrete is below
successfully',', exposed joints in such construction may
standard or if especially adverse factors exist at the time
be very carefully sealed and drainage must be provided
of the freezing thaw cycles the effects may be serious.
where joints can be damaged by freezing of accumulated
Concrete which will be exposed to frost action should
water within the joints.
have durable aggregates, 4 to 7 percent entrained air
(5) Unless favorable foundation conditions
depending on aggregate gradation, proper consistency
exist or can be provided, concrete block or brick
for good placement without segregation, adequate
masonry construction should be avoided because of its
curing, and best possible drainage afterwards. Concrete
poor ability to tolerate differential movements. When
which is saturated prior to freezing tends to be more
masonry is used for interior work, environmental
susceptible to freeze-thaw damage. For large or critical
protection must be
exposed structures, investigation and testing of available
aggregates including freeze-thaw testing, petrographic
2-33