Nanoclay-modified asphalt mixtures for eco-effi cient construction - Nanotechnology in Eco-efficient Construction - page 111

Chen et al. (2002) showed that SBS improved the rheological properties of
asphalt binder due to the formation of a polymer network in the binder.
This network forms in two stages: at low polymer concentrations, the SBS
acts as a dispersed polymer and does not signifi cantly affect properties; at
higher concentrations, local SBS networks begin to form and are accompa-
nied by a sharp increase in the complex modulus, softening point tempera-
tures, and toughness.
Radziszewski (2007) studied mechanical properties of asphalt mixtures
containing elastomer, plastomer and fi ne rubber modifi ed binders. His study
showed that while being exposed to simulated short-term ageing and long-
term ageing, asphalt mixtures behave differently in terms of rutting and
creeping. Ageing causes higher stiffness with unmodifi ed binder mixtures
than with polymer or rubberized bitumen modifi ed binder mixtures. Per-
manent deformation depends on the type of asphalt mixture and the type
of binder used. Asphalt concrete with rubberized bitumen, asphalt concrete
with 7% polymer modifi ed binders and SMA and Superpave mixtures with
unmodifi ed binders appeared to be most resistant to permanent deforma-
tions after long-term laboratory ageing (Radziszewski, 2007).
Recently, nanoscale inorganic fi llers have drawn increasing interest as it
is theoretically possible to signifi cantly improve the properties of pristine
polymers such as bitumen with a relatively small percentage of additive
(Lan and Pinnavaia, 1994; Lan et al. , 1995, Kornmann et al. , 2001; Zerda and
Lesser, 2001; Becker et al. 2002, Liu et al. , 2003). Nanoclays are micro-scale
fi llers which would make polymers effi cient as fi ller reinforcements. Ghile
(2005) performed mechanical tests on asphalt mixture modifi ed by Cloisite.
The results showed that nanoclay modifi cation can improve mechanical
behaviour properties of the mixture such as indirect tensile strength, creep
and fatigue resistance. Chow (2003) investigated surface modifi ed montmo-
rillonite nanoclay and compatibilizer, and found that the strength and stiff-
ness of polyamide polypropylene nanocomposites improved due to the
synergistic effect of surface modifi ed montmorillonite nanoclay and com-
patibilizer. Yasmin et al. (2003) found that the addition of Nanomer I.28E
and Cloisite 30B into some pure epoxy polymers produced materials with
higher elastic modulus than that of the pure epoxy.

￿ ￿ ￿ ￿ ￿ ￿

6.3 Material and methods

The aggregates used in this study were crushed limestone aggregates with
gradation characterized by 12.5 mm nominal size (according to Pavement
Guidelines in Iran) and limestone mineral fi ller. Physical properties of the
aggregate, both coarse and fi ne, together with mineral fi ller are given in
Table 6.1 and aggregate gradation shown in Fig. 6.3. The bitumen was a
60/70 penetration grade (AC-10) and its properties are shown in Table 6.2.