UFC 3-260-03
15 Apr 01
7. RECOGNITION OF POTENTIAL FOR DETRIMENTAL FROST ACTION. There are several ways to
recognize either existing or potential frost action on pavements.
a. Visible surface effects associated with frost action include pavement heave and cracking during
the freezing season and noticeable weakening or deflection during the frost-melting period. Pavements
that are experiencing accelerated distress because of thaw weakening may also show alligator cracking or
other load-associated cracking at an early age. Pumping may take place at cracks and joints. During
pavement inspections, particular attention should be given to locations of transitions between cuts and fills
and also at any boundaries of subgrade soils of varying frost susceptibility. One common indication of
freeze-thaw damage to PCC pavements is the appearance of D (Durability) cracking. These are closely
spaced cresent-shaped cracks that occur adjacent to longitudinal and transverse joints or free edges.
b. The construction, maintenance, and previous evaluation records of the airfields may help in
confirming whether or not frost-susceptible conditions exist. Records of highway performance in the
vicinity of the airfield that have similar subgrade conditions may provide a clue as to whether weakening
occurs as a result of frost melting. In the analysis of highway performance records, the evaluator should
carefully note and assess the many local influences that may affect frost action, such as variations in
ground-water level, soil conditions, type of pavement surface, degree of shading, north versus south
slope, frequency of snow plowing, position of underlying bedrock, etc.
c. Supplementary field and laboratory investigations to determine if detrimental ice segregation and
thaw weakening are likely to occur in the base course, subbase course, or subgrade should be made, in
addition to the basic investigations specified in chapter 3. With time, base and subbase materials can
become degraded due to freeze-thaw cycles and traffic loads. The degradation may introduce additional
fines, thus increasing its thaw-weakening potential. Before rehabilitation, the gradation and frost
susceptibility of the base/subbase material should be determined and compared with the original
as-constructed classifications. If any of the materials classify as possibly frost susceptible (PFS), a
laboratory frost susceptibility test should be conducted to properly classify the material to estimate its
strength during thawing periods. At the time of maximum heave, the surface roughness of pavements
constructed over F4 subgrade soils, and in some instances over F3 soils may be objectionable for aircraft
with high landing and takeoff speeds. If experience indicates this is the case, it should be indicated in the
evaluation report, and the report should include the locations and descriptions of the objectionable
roughness. Surface elevations should be obtained at least once a month during the following winter to
determine the magnitude of the detrimental heave.
8. PAVEMENT EVALUATION-GENERAL. The procedure for pavement evaluation in cold regions is
illustrated in figure 7-4. Pavements in seasonal frost areas are evaluated using a stepwise procedure.
The first step is to determine if the pavement structure is completely protected from frost action. If it is
not, the second step is to determine if the thickness is adequate for limited subgrade frost penetration; if
not, the third step is to apply the reduced subgrade strength procedure for the pavement evaluation or
reduced modulii for NDT evaluation. Agencies may vary the procedure based on their experience.
Standard pavement evaluations conducted by DOD normally do not include step 2, limited frost pene-
tration. If the pavement thickness is adequate for complete protection or limited subgrade frost penetra-
tion and no effects of frost action are apparent, the pavement is evaluated using nonfrost criteria. If any
pavement feature evaluated at an airfield is adequately protected against frost action, a discussion to that
effect will be included in the text of the report. Appropriate notes should also be included in tables of the
report.
9. DETERMINE DESIGN FREEZING INDEX (DFI). The DFI is the average air freezing index of the
three coldest winters in the last 30 years of record. If 30 years of record are not available, the air freezing
index for the coldest winter in the last 10-year period may be used. If either data sets are not available, an
approximate freezing index may be obtained from the map in figure 7-2 showing design air freezing
indices for locations in North America. Special consideration will be necessary to compensate for local
7-4
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