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

design specifications are meticulously prescribed, implemented, and verified by the
highway agency (68).
2.5.3 Slurry Seals and Microsurfacing
Slurry seals consist of a homogeneous mix of crushed aggregate and an asphalt
emulsion which is applied to the pavement surface as a single-pass monolayer. Curing
of the slurry seal coat occurs as the water evaporates, leaving only the residual asphalt
to coat the aggregate surfaces. In general, slurry seals contain a high proportion of
fines which generally yields a highly skid-resistant surface. In addition, slurry seals also
improve water- and skid-resistance, but most are generally applied to only lower-volume
(i.e., < 1,000 ADT) roads.
Microsurfacing is a commonly used form of slurry sealing consisting of a combination of
mineral aggregate and fillers, a polymer modified asphalt emulsion, and other additives.
The primary difference between microsurfacing and most other forms of slurry sealing is
the thickness. Slurry seals are generally laid at 1-1.5 inches in thickness, whereas
microsurfacings are thickly applied in multiple layers. In addition, the PME used in
microsurfacing are broken chemically instead of through evaporation which is used in
most other asphalt emulsion applications. This permits the microsurfacing to gain
cohesive strength rapidly, thereby minimizing lane closures and traffic delays (69).
Microsurfacing is commonly used to correct wheel-path rutting and improve skidresistance,
and can be applied to either high or low volume roadway pavements (40,
70). Takamura (n.d.) reports that polymer enhanced microsurfacings can be used to fill
ruts up to 5 cm in depth using a rut-box (54). When applied in rut-filling applications, it
is desirable to assess the rut-resistance potential of the PME (at a minimum) through
the performance of DSR testing on the extracted asphalt residue (48, 49, and 54).
Takamura (n.d.) also provides comparisons of the effects of microsurfacing curing
between mixtures containing varying polymer concentrations (54). Figure 21 illustrates
the change in rutting resistance temperature versus curing time for 5% and 3% polymer
contents in microsurfacing mixtures. As has been noted previously, increases in rutting
resistance are evident in both mixtures as curing time increases. Moreover, note also
that although the rutting resistance for the 5% mixture is improved over the 3% mix, the
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