UFC 3-250-03
15 May 2001
pavement temperature is about -30EC (-22EF). Table 2-4 shows that this cold region can be further
classified as a moderately cold region since its DFI is less than 1,667 degree-Celsius-days. Table 2-4
also indicates that the required PVN of the asphalt selected must be greater than !0.5 for a design index
of 10. This will minimize low temperature pavement cracking. Now, PVN values must be determined for
the available asphalt cements. This can be done by either plotting penetration and viscosity at 135EC
(275EF) in figure 2-3 or by using PVN equations. If the details of figure 2-3 are not sufficient to
accurately determine PVN values, equations should be used. The general PVN equation is as follows:
(L & X) (&1.5)
PVN '
(L & M)
where
L = logarithm of viscosity in centistokes at 135EC (275EF) for a PVN of 0.0 at the given
penetration
X = logarithm of viscosity in centistokes at 135EC (275EF) of a given asphalt
M = logarithm of viscosity in centistokes at 135EC (275EF) for a PVN of -1.5 at the given
penetration
Values of X can be determined directly from asphalt cement viscosity data as provided in this example,
but values of L and M are a function of the penetration values of each asphalt. Equations for the values
of L and M are:
L ' 4.25800 & 0.79674 LOG (PEN)
and
M ' 3.46289 & 0.61094 LOG (PEN)
where PEN = penetration at 25EC (77EF) of a given asphalt cement.
Calculated PVN values of the two available asphalt cements are:
PVN = -0.638 for AC-2.5
PVN = -0.081 for AC-5
Based on table 2-4, an asphalt cement that has a PVN greater than -0.5 and lies on or to the right of the
minimum temperature diagonal line should be selected. The AC-5 asphalt cement is selected because it
has a PVN of -0.081 and lies to the right of the -30EC (-22EF) temperature diagonal line. This asphalt
cement satisfies the requirements of table 2-4 and should prevent low-temperature pavement cracking.
(4) SHRP performance grading (PG) of asphalt cements.
(a) General. The SHRP PG system (AASHTO MP1-93) classifies asphalt binders
according to the temperatures at which certain performance-related properties are met (AASHTO PP6-
93). These specifications will have replaced penetration and viscosity graded asphalts. The
specifications can be applied to unmodified and modified asphalt cements. The SHRP performance
grading procedures must be applied with caution to certain polymer modified asphalts binders (PMAB).
The SHRP PG specifications are built around viscoelastic properties such as complex modulus, G*,
2-11
Previous Page
