Using Polymer Modified Asphalt Emulsions in Surface Treatments A ...

2.2.3 Synthetic Rubber and Latex
Synthetic latex is a thermoset elastomer which consists of a mixture of polymer particles
dispersed in water. Commonly used varieties of synthetic latex rubber include styrenebutadine
rubber (SBR, a random copolymer), polychloroprene (Neoprene), and
polybutadiene (PB). Common uses of latex modified asphalt emulsions include
microsurfacings, chip seals, and slurry seals. Lubbers and Watson (2005) note that the
handling and blending of SBR latex is particularly versatile, and is amenable to a variety
of pre- and post-modification methodologies (4). When sufficient quantities of synthetic
latex are added to compatible asphalts, the cured mixture is commonly characterized by
the existence of a continuous polymer network which envelops the bitumen particles
(see Figure 4). Benefits of properly blended latex polymers included improved stone
retention, increased skid-resistance, and improved low temperature performance (i.e.,
less brittleness, better elasticity).
Like NRL, when SBR latex is uniformly dispersed in the emulsion during blending, it
forms elastic lattices within the bituminous cement when cured. More specifically, as
water within an applied emulsion evaporates, droplets containing SBR coalesce along
the surfaces of asphalt particles, which results in the formation of a continuous,
honeycombed polymer network which extends throughout the binder (12). In this way,
SBR particles form “welds” between asphalt particles, which results in an increase in
tensile strength, stone retention, and resistance to cracking (12) (13). SBR
modification of asphalt emulsions may be accomplished by co-milling at the colloid mill,
post-blending after emulsification, or by mixing at the application site through the
distributor (a field variation of the post-blending method) (13). SBR compatibility with
the asphalt used should be verified to ensure the success of single-stage mixing
methods.
Takamura (2001) has demonstrated the benefits of performing SBR modification of
asphalt emulsions and microsurfacing mixes, in which significant increases in rutting
resistance were observed with increasing polymer content (14). Takamura notes that
as curing time lengthens, the benefits of increased polymer content become more
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