Effects of alternative polymer modifications on cracking performance of asphalt binders and resultant mixtures

The use of styrene-butadiene-styrene (SBS) polymer-modified asphalt (PMA) binder has successfully enhanced pavement cracking performance. Meanwhile, state agencies hesitate to allow the use of alternative PMA binders that meeting existing specification requirements for PG 76-22 SBS PMA binder, due to a lack of experience and documented performance. A previous study identified four out of seven alternative PMA binders that exhibited excellent elastomeric behavior and fracture properties. This study extends these prior efforts by assessing whether binder results translate to improved cracking performance of resultant mixtures. Superpave indirect tension (IDT) tests were conducted to obtain the fracture properties of asphalt mixtures with the four alternative PMA binders, as well as a standard PG 76-22 (3% SBS) PMA binder and a PG 67-22 unmodified base binder. Results showed that these alternative PMA binders, produced with SBS plus polypropylene composite, terpolymer plus polypropylene composite, SBS plus oxidized polyethylene wax and a fourth non-SBS polymer of unknown composition, not only reduced the rate of damage accumulation but also improved the failure limit of the resultant mixtures. The energy ratio (ER) parameter which has been closely tied to field pavement cracking performance was calculated for each mixture, and the results showed that these alternative PMA binder exhibited equivalent or better cracking performance than the PG 76-22 SBS PMA binder. Finally, the binder fracture energy density (FED) results satisfactorily rank mixture cracking performance thereby supporting the use of the binder fracture energy (BFE) test as an effective tool to quantitatively evaluate the relatively cracking performance of asphalt binder.