State Study 111 - Polymer Modified Hot Mix Asphalt Field Trial.pdf

CONTROL Section
Both the binder and surface test values were acceptable. Stability was low for both mixes.
ROTATIONAL VISCOMETER TESTS
The rotational viscometer was used as part of SHRP Binder Tests to determine viscosity
of the different modifiers. Figure 16 displays the viscosity with respect to temperature for
the binder courses. At the lower temperature of 275 O F the modifiers are all spread out
ranging from a high viscosity value of 2600 cP for MULTIGRADE to a lower value of 500
cP for the CONTROL Section. All of the modifiers have higher viscosity at the lower
temperature than the AC30 in the CONTROL. However, at the higher temperature of 374 O
F, all of the modifiers are bunched together ranging from a high value of 400 cP for the
NOVOPHALT modifier to a lower value less than 100 cP for the CONTROL and
MULTIGRADE. The modifiers are all more viscous at the lower temperatures whereas the
AC30 without a modifier did not change much in value.
A similar chart is shown in figure 17 for the surface course with the results being the same
as for the binder course, i.e., scatter of the data at the lower temperature and a bunching
of the data at the higher temperature. MULTIGRADE, which is a gel, had a very high
viscosity at the lower temperature but has the lowest at the higher temperature. The
unmodified AC30 did not change much with increase in temperature.
GYRATORY COMPACTOR TESTS
The SGC was also used as part of the SHRP binder tests to determine densities on 6 in
diameter pills at 7 percent air voids. Twenty-four samples were made for each modifier for
the right lane pavement and these samples were to be tested later in the Asphalt
Pavement Analyzer to determine rutting resistance of each modified HMA.
GYRATORY TEST MACHINE TESTS
The US Army Corps of Engineers GTM was used to determine shear strength and air
voids with respect to revolutions. Shear strength was calculated using the force diagram
and equation from reference 1. The force diagram for computing shear strength has been
reproduced and is shown in figure 18. Referring to the force diagram and taking moments
about O (while neglecting wall friction and moment N x b), the formula for Gyratory shear
(S G ) determined as follows:
where:
S G = 2 WL / Ah
W = p x a = Load on roller
L = Length of roller lever arm
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