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

of residual asphalt (3). Additionally, as the swelling of the polymer components of a
modified emulsion increase, less polymer additive is needed (by weight) to achieve c*.
Polymer swelling is generally believed to be caused via interaction with aromatics
contained within maltene fractions, and will eventually lead to the formation of a
continuous network (18).
Factors influencing the c* include the quantities of diblock (SB) versus triblock (SBS)
copolymer used, mixing temperatures, the chemical compatibility between the asphalt
and polymers utilized, and blending time (3). Within this context, “compatibility” refers to
the degree of molecular interaction occurring between the asphalt and polymer modifier
components of the mixture, with more compatible asphalt being characterized by a
higher degree of polymer swelling and increased homogeneity and dispersion of the
polymer fractions when mixed. In this regard, block copolymer modifiers must be
matched to compatible asphalt which will readily dissolve the end-block styrene
domains at typical mixing temperatures, as this ensures thorough dispersion of polymer
chains during the emulsification and milling process (3).
Stroup-Gardiner and Newcomb report that the complex modulus of 6% SBS-modified
AC-10 decreases significantly with increasing SB diblock content at higher temperatures
(3). Moreover, the researchers note that as the concentration of the diblock SB
increases within an SBS modifier, the resultant complex modulus decreases
substantially, leading to increased pavement rigidity, particularly at higher temperatures
(3).
Studies by Serfass et al (1992) show that SBS-modified asphalt emulsions exhibit
excellent adhesion properties with a diverse variety of aggregate, and can be applied
over a much longer working season than similarly modified hot mixes (19). Moreover,
emulsified asphalt applications were also shown to tolerate higher polymer dosing levels
than modified hot mixes, resulting in improved stone retention, cohesive, and
viscoelastic properties; especially in crack sealing applications.
Investigation into the effects of SBS and SEBS triblock copolymers on asphalt rheology
conducted by Gahavari (1997) shows a substantial increase in complex moduli at low to
18