TM 5-852-4/AFM 88-19, Chap. 4
d. In permafrost areas, deep fills constructed
head can develop, destroying its water-tightness. If the
section is heavy enough so that only a thin layer of poor
with thawed materials may require up to many years to
mortar is produced on the face of the concrete by the low
freeze to the ultimate thermally stable condition, if placed
temperatures, it may sometimes be acceptable to place
by single-step construction. When this slow, long-term
concrete directly against frozen soil, provided the soil
freezing is likely to result in undesirable frost heaving,
supporting the foundation is not susceptible to settlement
consideration should be given to placement of fill in
on thaw. When underlying soils contain sufficient ice so
annual increments, each of which will freeze completely
that settlement will occur on thaw, special pads of wood,
during the winter following its placement. The result will
gravel and/or rigid insulating material or their
be a more immediately stable foundation, upon
combinations, of adequate bearing strength, should be
completion. An example of this procedure was the two
used between the frozen ground and the concrete
stage construction of a runway extension embankment at
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course to protect the frozen ground from thawing and to
Sondrestrom Air Base, Greenland . Inorganic soils are
aid in retention of heat by the concrete. Wherever
very often covered with living "tundra mat," a mantle of
concrete must rest on or adjacent to frozen soil, strong
moss and peat. In permafrost areas this material should
consideration should be given to the use of precast
usually be left in place during the placement of fill, thus
sections to avoid the problems of protection, to insure
preserving to a limited extent its value as an insulating
quality construction and to minimize work schedule
layer. The natural cover around a construction site
problems. On important work, refrigeration pipes placed
should be protected from disturbance by construction
within a granular course have been employed to maintain
equipment, to minimize subsequent degradation. Cutting
the 32 F point on the temperature gradient at the proper
of the tundra mat by heavy tracked vehicles is a common
position between the underlying permafrost and overlying
source of local thawing and subsequent ponding of
newly cast concrete. Electrical heating cable may also
water, erosion and degradation of permafrost.
e. The design should take into account the
be used where supply of heat is necessary. Artificial
refrigeration placed within the concrete has much more
possible frost heave of backfill and the effect of such
limited utility, as such refrigeration cannot be turned on
heave on footings, structural elements, utility connections
until the concrete has gained minimum required strength
and walls. Backfill adjacent to walls should be non-frost
and in this time excessive thaw settlement of underlying
susceptible in situations where frost heave or frost thrust
materials may occur if ground ice is present.
damage might otherwise occur.
f.
(2) Plans to protect fresh concrete from
Determination of construction material
freezing and to maintain temperature at not less than the
availability is an essential element in the design effort. If
specified permissible minimum should be made well in
special materials such as non-frost-susceptible backfill
advance of expected freezing temperatures.
All
are only accessible at specific times of the year, this may
necessary equipment and materials should be ready for
be a critical factor in design decisions.
use at the site of the work before concrete placing is
permitted. It is too late to start assembling protective
6-4. Placing concrete under freezing air or ground
devices and materials after concrete placing has
temperature.
commenced and the temperature begins to approach the
a. General.
Under freezing conditions,
freezing point. The complications which these measures
concrete placement should conform to standard
introduce can be greatly reduced by maximum
procedures, but additional special precautions should be
22,115,203.
employment of prefabricated components and members.
employed as needed to assure good results
(3) "Concrete which is not allowed to
(1) As a general rule, concrete should not
freeze and which is placed at low temperatures above
be placed in direct contact with ground or rock at
temperatures below 33 F. If the concrete section is thin
freezing, and receives long-time natural curing, develops
higher ultimate strength, greater durability, and less
and the temperature of the ground well below freezing,
thermal cracking than similar concrete placed at higher
the concrete may freeze or at least may not set and
temperatures. A high concrete temperature as placed
harden properly. If the concrete section is massive, its
will impair these good properties, although it may
heat of hydration will generate ample heat for strength
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expedite small jobs and finishing in cold weather."
gain and prevention of freezing but this heat may at the
Concrete mixed and placed at a high temperature also
same time thaw the ground for some depth and this may
requires excessive mixing, requires a higher water
result in settlement and formation of voids even while
content to maintain a specified consistency, and usually
work is in progress, if ground ice is present. The
results in quick setting. Rapid moisture loss from hot
concrete may be fractured, foundation bearing capacity
concrete surfaces or high temperature differentials at the
may be reduced, and it may become impossible to
maintain foundation grade lines. Thaw water may pipe
up through the fresh concrete before set if a pressure
6-4
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