TM 5-809-1/AFM 88-3, Chap. 15
4-3. Environmental conditions.
economical means of maintaining a stable thermal
regime in permafrost under slabs-on-grade is by
a. Freezing and thawing. Special additional
means of a ventilated foundation. Provision is made
design considerations and measures are necessary
for ducted circulation of cold winter air between the
where freezing and thawing may occur in underlying
insulated floor and underlying ground. The air
soils. The effects of such occurrences, which are
circulation serves to carry away the heat both from
termed "frost action," include surface heaving
the foundation and the overlying building, freezing
during freezing and loss of bearing capacity upon
back the upper layers of soil which were thawed the
thawing. Detrimental frost action is the result of the
preceding summer. The characteristics of permafrost
development and/or thawing of segregated ice in
and engineering pinciples in permafrost regions are
underlying soils. Potential difficulties from frost
described in TM 5-852-1/AFM 88-19, Chap. 1, and
action exist whenever a source of water is available
TM 5-852-4.
to a frost-susceptible soil which is subject to
d. Applicable technical manuals. Where freezing
subfreezing temperatures during a portion of the
and/or thawing may occur in underlying soils, slab
year. Conditions necessary for the development of
design will be in accordance, as applicable, with TM
ice segregation in soils together with a description
5-818-2/AFM 88-6, Chap. 4 and TM 5-852-4.
of the ice segregation process and the detrimental
Thermal computatio procedures are detailed in TM
effects of frost action are given in TM 5-818-
5-852-6/ AFM 88-19, Chap. 6.
2/AFM 88-6, Chap. 4.
b. Cold storage facilities. A somewhat different
4-4. Concrete strength.
problem is encountered in cold storage facilities
a. General. For a given water-cement ratio, the
where a structure in contact with the ground is
maintained at subfreezing temperature. Thus, frost
concrete strength likely to be obtained in a given
action under such structures is a long-term rather
locale depends primarily on the aggregate sources
than a seasonal phenomenon, and deep frost
available. Maximum particle size and quality of the
penetration will eventually result, even in areas
coarse aggregate will have a pronounced effect on
where subfreezing ground temperatures are not
concrete strength as will the gradation of the
naturally experienced, unless insulation or
blended coarse and fine aggregate. In general,
provisions for circulation of warm air beneath the
aggregates of the bankrun variety, as opposed to
slab are provided in design. Recommended as a
crushed aggregates, will produce a lower-strength
reference is American Society of Heating,
concrete due to particle shape. Specified concrete
Refrigerating, and Air-Conditioning Engineering
strength should be sufficient to provide high wear
ASHRAE Handbook and Product Directory,
resistance properties, constructability, and a
Equipment, and Applications, (see Biblio). It should
reasonably high flexural stress to attain the greatest
be kept in mind that insulation may merely slow
economy in the design. A study should be made of
frost penetration. It does not prevent heat flow.
the strengths likely to be encountered, since
c. Permafrost. Since construction alters the ex-
specifying an unusually high-strength concrete mix
isting thermal regime in the ground, an additional
may result in a higher material cost for the project.
b. Traffic types. The minimum concrete compres-
problem is encountered in regions where heat flow
from the facility may result in the progressive thaw-
sive strength for floors subjected to pneumatic tired
ing of perennially frozen ground (permafrost). Ther-
traffic will be 4,000 pounds per square inch; for
mal degradation of permafrost which contains
floors subjected to abrasive traffic such as steel
masses of ice will result in subsidence as well as
wheels, the minimum concrete compressive strength
reduction in bearing capacity. Both may be severe.
will be 5,000 pounds per square inch.
The most widely employed, effective, and
4-3
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