(0.78 103 in.). Since the FAA specifications
208 specifications. Field test data showed a
for the remaining materials gave no infor-
reduction in the bearing capacity of base and
mation on the percentage finer than 0.02
subbase materials that ranged from 13 to
mm, the percentage passing the no. 200
60%.
sieve was used to determine frost-suscepti-
For stabilized materials, we found that the
bility. However, this has been found to be
results of the ASTM (1992c) D-560 durability
conservative, i.e., materials that would pass
test can be used to infer the frost-resistance
the COE criterion failed the percentage
(thaw-weakening) properties of the material.
passing the no. 200 criterion. Using the
Data were found that clearly showed the
Asphalt Institute criterion, we evaluated the
reduction of strength as a function of freeze
remaining base and subbase materials and
thaw cycles for lime-treated soils. For cement-
found that, within the limits specified, the
treated soils, we found that the tensile strength
remaining unstabilized materials were
of the material decreased with increasing
frost-susceptible.
freezethaw cycles. We also found that when
We also found that for oolitic limestone, the
15% cement was added to the soil, there was
percentage passing the no. 200 sieve had no
no reduction in the tensile strength after 12
influence on frost heave, although this was
freezethaw cycles. The resilient modulus of
not the case for hard limestone. For the
cement-treated soils remained at its before-
oolitic limestone, the amount of moisture
freeze level when cement contents greater
present in the layer had a significant effect
than 5% were added to the soil. Although the
on frost heave. This finding also probably
modulus was the same, the strength of the
applies to the caliche and shell base materi-
material decreased. The permeability in-
als. Addition of slag as substitute aggregate,
creased in soils treated with up to 6% lime.
up to 50%, was found to reduce frost heave.
No information was found on the thaw-
For the frost-susceptibility of stabilized
weakening characteristics of cement-treated
(lime and portland cement) soils, the data
bases and econocrete subbases.
showed that a minimum of 3% lime or
cement is required to reduce frost heave by
about 50%. The addition of a pozollith to
RECOMMENDATIONS
lime or cement appeared to reduce frost
The results presented in this report are based on
heave significantly in ML and CL soils. In
limited information found in the literature, so
cohesionless soils, it was reported that
actual laboratory and field tests should be con-
about 3 to 8% cement is required to reduce
ducted to validate some of the findings. In any
frost heave. For frost-susceptible gravel
case, the following recommendations are made.
soils, 2% cement is required to change it to a
The COE frost-susceptibility criterion should
non-frost-susceptible material.
be included in all appropriate FAA specifica-
Thaw-weakening of the base material was
tions.
inferred from the time it took to drain an air-
For reducing frost heave and the thaw-
port pavement by 20, 50, and 100%. The
weakening period, the amount passing the
COE drainage requirement is that 50% of
no. 200 sieve should be kept below 2%. We
the base be drained within 10 days. We used
highly recommend that drainage layers,
the drainage model developed by Casa-
meeting the COE criteria, be included in
grande and Shannon in this study, finding
future airport pavement design and con-
that none of the materials passed the COE
struction in cold regions. Drainage layers
criterion. Some of the materials came close
should be placed below the pavement sur-
to it, suggesting that if the fines contents
face and at the top of the subgrade.
were further reduced to 2 or 3%, they may
An effort should be made to develop engi-
come close to meeting the criterion. As for
neering properties of both unstabilized and
the P-213 material, the base appeared to re-
stabilized base and subbase materials sub-
main saturated all year round. This material
jected to freezethaw cycling. This was
should not be used in seasonal frost areas.
Available data showed a hundred-fold
found lacking in the literature. These data
will be critical to the development of the FAA
reduction in the frozen and thawed modu-
mechanistic design procedure.
lus of materials that meet the P-154 and P-
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