Table 18. Performance predictions for F3 test section with water table at 2.4 m
(8 ft). Freeze/ thaw seasons applied as upper boundary temperatures were mean
year (195960), maximum year (197879), minimum year (198687), average of
the 3 coldest out of 30 (196465).
Applications to failure (1000)
Failure criteria
Mean
Max
Min
3/30
Horizontal
Asphalt Institute (MS-1)
533
384
573
397
Asphalt Institute (MS-11)
1,224
1,215
1,117
1,445
Corps of Engineers
487
375
593
368
Coetzee/Conner
32,818
25,284
50,660
23,530
Vertical
>107
Asphalt Institute (MS-1)
96,046
51,120
96,046
>107
Corps of Engineers
1,197
600
1,143
>107
FAA
7,298
4,080
7,625
Note: Traffic simulated at rate of 562,830 ESAL applications/yr.
warming that remained above freezing. The mini-
damage due to subgrade rutting was predicted with
mum year had several freeze/thaw events, but they
the minimum year in which no frost penetrated
were less severe--none of them penetrated be-
the subgrade.
yond the base course materials. The maximum
year began with a very severe freeze event that
Phase 3
penetrated to the subgrade and lasted all winter. In
The third phase of the study modeled two flex-
the spring, thawing of this freeze bulb was inter-
ible pavement sections to which 21 years of envi-
rupted by two smaller freeze events, such that there
ronmental conditions were applied. Various analy-
existed a thawed layer in the subbase between two
ses were conducted attempting to correlate the
frozen zones. The year with a freezing index equal
predicted damage with the characteristics of the
to the mean of the three coldest in 30 (3/30 year)
freeze seasons simulated.
had a freeze season consisting of a single severe
freeze event that penetrated into the subgrade,
Cross sections/Material properties
which then thawed with no small freeze events.
The two cross sections simulated employed layer
Table 18 lists the predicted damage in terms of
thicknesses from two Mn/ROAD test sections. The
applications to failure from this environmental se-
first, section F4, was a "full-depth" section con-
ries, in which traffic was simulated at 562,830
sisting of an asphalt layer lying directly above the
ESALs per year. Compared with the mean year,
lean clay subgrade. The second, section F3, was a
failure due to the horizontal strain criteria (asphalt
"conventional" section, including class 6 special
cracking) is predicted earlier with the maximum
as the base material (substituted for class 5 special
year and the 3/30 year, and later with the mini-
in the actual pavement structure) and class 3 spe-
mum year. However, the spread of values is not
cial as the subbase.
that great, and three of the four models predict
Physical properties used for the materials were
failure sooner than the design figure of 3,300,000
the same as shown in Table 14, with the exception
that a lower density (1.69 Mg/m3, 105.5 lb/ft3)
applications for all four of the seasons modeled.
was used for the 1206 subgrade (Fig. 15). The as-
Time of failure due to the vertical strain criteria
phalt modulus was calculated with a combination
(asphalt rutting) is predicted sooner in the maxi-
of the Ullidtz model at above 1C temperatures
mum year than the mean year, and at about the
and the Schmidt model at colder temperatures.
same time as the mean year with the 3/30 year. No
37
Previous Page
