Polyphosphoric Acid in Combination with Styrene-Butadiene-Styrene Block Copolymer - Laboratory Mixture Evaluation

摘要

State Agencies in the United States have known for years the benefits associated with asphalt binders that are modified with elastomer-type polymers to improve the rutting and fatigue cracking properties of the hot mix asphalt. However, in recent years, a majority of asphalt binder suppliers are now using polyphosphoric acid (PPA) in combination with decreased percentages of polymers to meet various performance graded asphalt binder requirements. This has raised concerns among the State Agencies in fear that the combination of PPA and reduced polymer percentages will result in an inferior asphalt binder when compared to the same asphalt binder solely modified by polymer. To help answer this question, a research program was developed to examine and compare the laboratory properties of an asphalt binder modified with and without PPA. Asphalt binder testing, consisting of continuous PG Grading and Multiple Stress Creep Recovery, and asphalt mixture testing, consisting of Dynamic Modulus and Flexural Beam Fatigue tested at both short and long-term aged conditions, as well as repeated load testing to evaluate permanent deformation were conducted on a base binder and the base binder modified in two manners; SBS polymer only and reduced SBS polymer + PPA. The paper presents the findings of the asphalt binder and asphalt mixture evaluation and shows that the use of PPA in formulation with SBS provides an equal performance, with respect to HMA mixture rutting, fatigue performance, and resistance to moisture damage, to the highly SBS modified asphalt binder.