Multiple Stress Creep–Recovery Test of Ethylene Vinyl Acetate and Polyphosphoric Acid-Modified Binder

The effect of longer creep and recovery times—from $1/9$ to $2/18$ s—on the percent recoveries (R) and the nonrecoverable compliances ($J_{nr}$) of some modified asphalt binders was investigated. A $50/70$ base asphalt cement [AC, penetration grade (PG) 64-xx] was modified using ethylene vinyl acetate (EVA) copolymer, polyphosphoric acid (PPA), and a combination of both additives to produce the $\mathrm{AC}+\mathrm{EVA}$, $\mathrm{AC}+\mathrm{PPA}$, and $\mathrm{AC}+\mathrm{EVA}+\mathrm{PPA}$ formulations, respectively. These formulations have the same high PG grade in the original Superpave specification (PG 76-xx). All the materials were tested at five equally spaced temperatures ranging from 52 to 76°C. The base binder experienced a decrease in its rutting potential after the addition of modifiers because the $R$ values increased and the $J_{nr}$ values decreased at typical high pavement temperatures. Unlike the other asphalt binders, the $\mathrm{AC}+\mathrm{EVA}$ showed small increases in $R$ and slight decreases in $J_{nr}$ at lower temperatures (up to 64°C) with increasing loading–unloading times, which can be translated into minor reductions in its susceptibility to rutting when both times were doubled.