TM 5-822-13/AFJMAN 32-1018
CHAPTER 4
ELASTIC MODULI OF PAVEMENT MATERIALS
4-1. Climatic Factors.
In the design system, two climatic factors, temperature and moisture, are considered to influence the structural
behavior of the pavement. Temperature influences the stiffness and fatigue of bituminous material and is the
major factor in frost penetration. Moisture conditions influence the stiffness and strength of the base course,
subbase course, and subgrade. Temperature does not influence the stiffness and fatigue of the PCC, but tem-
perature differential in the concrete can cause the slab to warp and break easily. In concrete pavements, mois-
ture differential can also cause the slab to warp but the effect is relatively minor.
a. Design pavement temperature. Pavement is generally designed for two different failure modes. One is for
the shear failure in the subgrade and the other is for the fatigue cracking in the surface layers. The design
procedure requires the determination of one design pavement temperature for consideration of vertical com-
pressive strain at the top of the subgrade and horizontal tensile strain at the bottom of cement- or lime-stabi-
lized layers and a different design pavement temperature for consideration of the fatigue damage of the bituminous
concrete surface. In either case, a design air temperature is used to determine (figure 4-1) the design (mean)
pavement temperature. Temperature data for computing the design air temperatures are available from the
National Oceanic and Atmospheric Administration (NOAA) "Local Climatological Data Annual Summary with
Comparative Data." With respect to subgrade strain and fatigue of cement- and lime-stabilized base or subbase
courses, the design air temperature is the average of two temperatures: (1) the average daily mean temperature
and (2) the average daily maximum temperature during the traffic period. The traffic period is normally 1 month.
For consideration of the fatigue damage of bituminous materials, the design air temperature is the average daily
mean temperature. Thus, for each traffic period, two design air temperatures are determined. For design pur-
poses, it is best to use the long-term averages such as the 30-year averages given in the annual summary. As an
example, the determination of the design pavement temperatures for lo-inch bituminous pavement can be dem-
onstrated by considering the climatological data for Jackson, Mississippi as tabulated below. For the month of
August, the average daily mean temperature is 81.5 degrees F., and the average daily maximum is 92.5 degrees
F.; therefore, the design air temperature for consideration of the subgrade strain is 87 degrees F., and the design
pavement temperature determined from figure 4-1 would be approximately 100 degrees F. For consideration of
bituminous fatigue, the design air temperature for August in Jackson, Mississippi is 81.5 degrees F., resulting in
a design pavement temperature of approximately 92 degrees F. (from fig 4-1). These design pavement tempera-
tures are determined for each of the traffic periods.
Temperature, degrees F.
Month
Average Daily Maximum
Average Daily Mean
January
58.4
47.1
February
61.7
49.8
March
68.7
56.1
April
78.2
65.7
85.0
72.7
May
June
91.0
79.4
July
92.7
81.7
August
92.5
81.5
September
76.0
88.0
October
80.1
65.8
November
68.5
55.3
December
60.5
48.9
4-1
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