Impact Of Polymer Modification On Ideal Ct And I Fit For Balanced Mix Design

This study evaluated the impact of polymer modification, without changing the base binder, on the intermediate- temperature cracking resistance of asphalt mixtures characterized using the Indirect Tensile Asphalt Cracking Test (IDEAL-CT) and the Illinois Flexibility Index Test (I-FIT). Twelve asphalt mixtures prepared with two mix designs and six virgin binders (including two unmodified and four polymer-modified asphalt binders per mix design) were evaluated. Each mixture was tested at three binder contents and two temperatures: 25°C and an equal stiffness temperature (T=G*). In almost all cases, the polymer-modified asphalt (PMA) and unmodified mixtures with the same base binder had statistically equivalent IDEAL-CT and I-FIT results, indicating a lack of sensitivity to polymer modification. Increasing the binder content or adjusting the test temperature to T=G* did not discriminate the PMA and unmodified mixtures in the two tests. Interaction diagram analysis of the IDEAL-CT and I-FIT results showed that polymer modification generally affected the toughness and post-peak behavior of the mixture, but these effects tended to offset each other on the final cracking index parameters. Unlike the IDEAL-CT and I-FIT, the two cyclic loading tests evaluated in the study demonstrated the benefits of polymer modification. This discrepancy highlighted the potential limitation of the monotonic loading tests in assessing the fatigue cracking resistance of PMA binders and mixtures. Finally, asphalt binders extracted from the PMA versus unmodified mixtures with the same base binder showed distinctly different rheological properties, but these differences were not captured in the IDEAL-CT or I-FIT when the test variability was considered.