TM 5-852-4/AFM 88-19, Chap. 4
provided during the construction period. For exterior
considered a better determination of performance than
applications, the additional possibility of freeze-thaw
total amount of moisture absorption after freeze-thaw,
damage during the life of the structure must be
especially in those which absorb a great deal of
anticipated. Bricks which will be in contact with frozen
moisture.
Vermiculite concrete or other forms of
soil should be of SW (ASTM) grade or equivalent. The
lightweight concrete which will gradually absorb
mortar must be durable and moisture resistant.
substantial amounts of moisture when placed
d. Thermal insulating materials.
Thermal
underground are unsuitable as insulating material in
below-surface construction. To prolong effectiveness of
conductivity values of construction materials are usually
insulation underground, it should be placed in positions
given for the dry condition. However, many of these
offering minimum exposure to moisture and to moist
materials lose much of their insulation value if they
freeze-thaw conditions. Thus, from the point of view of
become wet. Many insulating materials will absorb
70,71,139
maintaining insulation effectiveness, incorporating
significant amounts of water (fig. 2-24 and 2-25)
insulation within a concrete foundation slab is preferable
and care should be exercised to select insulation
to placing the insulation in the ground below the slab. In
material for underground use which will absorb minimum
usages where complete moisture protection can be
moisture and to allow in the design for the degree of
readily provided, such as under the floor of a structure,
insulation impairment from moisture which is expected
any commercial insulation or insulating composition
over the life of the facility. Cellular insulations exhibit
suitable for general building usage may be employed
extremely varied performance and must be examined
provided it meets other applicable requirements such as
closely before acceptance for specific installation
bearing capacity or compression criteria.
Thermal
usages; details of manufacture may significantly affect
properties of a number of materials are given in TM 5-
moisture absorption rates. Cellular glass has performed
14
852-6/AFM 88-19, Chapter 6 . Insulation only slows
fairly well, though not perfectly, in maintaining its low
42,80
down rate of heat conduction; it cannot prevent heat flow.
. Both laboratory and field
conductivity in wet ground
When thick gravel pads contain some moisture, they
experiments show that cellular glass experiences slow
provide nonfrost-susceptible thermal buffers or heat
but progressive deterioration under wet freeze-thaw
sinks in which freezing and thawing are absorbed with
conditions. Table 2-3 shows field test data. Figure 2-
minimum detrimental effects; if freeze and thaw should
25d illustrates the effect of freeze-thaw on moisture
penetrate somewhat into the soil below such a gravel
absorption by various board-type insulations, but since
pad, the gravel layer helps to minimize frost heave and to
exposure to freeze-thaw in presence of water causes
smooth out any differential heave or settlement which
some cell damage in cellular insulations, thermal
may occur.
conductivity tests, after freeze-thaw cycles, are
2-35
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