Rheological and Chemical Properties of Hydrated Lime and Polyphosphoric Acid–Modified Asphalts with Long-Term Aging

The rheological and chemical properties of hydrated lime-polyphosphoric acid (PPA)–modified asphalt binders before and after laboratory oxidative aging were investigated through dynamic shear rheometer (DSR) and nuclear magnetic resonance (NMR) tests. Ten percent by weight of hydrated lime was mixed with 1.5% by weight of PPA-modified asphalt binders. The neat asphalts and multimodified asphalts were subjected to the pressure aging vessel test at a pavement service temperature of 60°C for different durations. The rheological properties of unaged and aged modified asphalts were measured with a DSR at various temperatures. NMR was used to investigate whether hydrated lime reacts with PPA. The rheological results indicate that the addition of hydrated lime to PPA-modified asphalt binders cancels the stiffening effect of PPA. In other words, the addition of PPA to asphalt increases the high-temperature performance grade (PG). The addition of hydrated lime to PPA-modified asphalt removes the benefit of the high-temperature PG that PPA provided. Furthermore, hydrated lime reduces the rate of oxidative age hardening. The interaction between hydrated lime, PPA, and asphalt binders is asphalt-type-dependent. The interaction between sol-type asphalts and hydrated lime and PPA is different from that of gel-type asphalts.