Rutting potential of Elvaloy® terpolymer and polyphosphoric acid-modified asphalt binders based on the MSCR test and the burgers model

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Matheus David Inocente Domingos
Adalberto Leandro Faxina

Asphalt binders play a key role in the resistance of the asphalt mixture to failure by rutting, fatigue cracking and low-temperature cracking. With respect to rutting, the multiple stress creep and recovery (MSCR) test has been taken by researchers worldwide as an interesting alternative to estimate the susceptibility of the material to the accumulation of permanent strain (Jnr – nonrecoverable creep compliance) and the level of its elastic response (R – percent recovery), as well as its stress sensitivity and degree of nonlinearity (Jnr, diff – percent difference in nonrecoverable compliances). In addition to these parameters, the four-element Burgers model has been commonly used in the literature to fit the repeated creep data obtained in this test. The present study utilized the MSCR test to analyze the creeprecovery behavior of asphalt binders modified with polyphosphoric acid (AC+PPA, PG 76-xx) and Elvaloy® terpolymer combined with PPA (AC+Elvaloy+PPA, PG 76-xx) at high pavement temperatures ranging from 52 to 76°C. A recent test protocol standardized by AASHTO (T350-14) was followed in the experiments, and rheological modeling of the data was made based on a seven-step procedure previously described elsewhere. Substantial increases in R and considerable decreases in Jnr are observed in the binder after the addition of PPA or a combination of Elvaloy® terpolymer and PPA, which can be translated into higher elastic responses (R values) and a much lower rutting potential in the field (Jnr values). This is especially remarkable for the AC+Elvaloy+PPA, which showed the best outcomes in the MSCR test, a high level of elasticity at the aforementioned pavement temperatures and a fairly low stress sensitivity. On the other hand, the parameter GV (viscous component of the creep stiffness) obtained from the Burgers model ranked the AC+PPA as the most rut resistant formulation at temperatures no greater than 58°C. Despite the fact that the results of the AC+PPA in the MSCR test are not as promising as the ones of the AC+Elvaloy+PPA, this formulation may be taken as an option to replace the base material on roads and highways with higher traffic levels and/or lower vehicle speeds, provided that the pavement temperatures are not higher than 64°C.

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