4. Summary and conclusions
The comparative laboratory investigation described in this
paper focused on the effects of commercially available polymers
as an additive for bituminous mixtures used as binder courses.
The analysis was divided into two main phases: the first one was
dedicated to the comparison of mixtures to which polymers were
added with standard and modified bitumen-bound mixtures; the
second one aimed at evaluating the effects of different types and
dosages of polymers on the corresponding mixtures by using simulative
mechanical tests.
Based on the results reported in this paper, the following conclusions
can be drawn:
the addition of polymers does not significantly affect constructability
parameters (k and C1) or the volumetric characteristics
(air voids, VMA and VFB) of the corresponding mixtures;
polymers grant the same benefits as modified bitumen in terms
of dynamic modulus; benefits increase when a high dosage is
used;
in terms of frequency sensitivity, polymers noticeably affect the
dynamic modulus of the corresponding mixtures. Specifically,
the master curves of mixtures containing polymers, especially
those with medium and high dosages (e.g. 6% and 9%) show a
reduction in stiffness at high frequencies (low temperatures);
whereas, at low frequencies (high temperatures), their behavior
is quite similar to the reference mixture (without polymers).Therefore,
in winter, a reduction in the propensity of a
mixture containing polymers for thermal cracking can reasonably
be expected;
fatigue life is generally improved by the presence of polymers,
thus a high dosage (9%) of polymer A (EVA) grants the best
performance;
the addition of polymers clearly benefits a mixture’s rutting
resistance, with the exception of the mixture with 3%
polymer B (LDPE) in which a slight reduction of RD and
WTS can be observed compared to the reference mixture
(without polymers). Generally, in summer, a reduction in
rut deformation proneness in mixtures containing polymers
is to be expected.
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