United States Department of Transportation
i
Elimination of Empirical, Ineffective and Expensive PG Plus Tests To Characterize Modified Binders
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2019-08-01
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[PDF-2.25 MB]
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Edition:Final Research Report Mar. 2018 – Mar. 2019
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Abstract:For characterizing the polymer modified binders, different state Departments of Transportation (DOTs) use different time consuming and empirical Performance Grade (PG) Plus test methods. Furthermore, the PG Plus tests are silent when asphalt binders are modified with chemicals such as polyphosphoric acid (PPA). But, the effects of the elastomeric or plastomeric polymer are not accurately identified through these conventional tests such as Elastic Recovery (ER) and tenacity. Thus, the main research goal of this study is to recommend alternative test method(s), which can possibly be pursued by using a commonly available device, a Dynamic Shear Rheometer (DSR). Three PG binders (PG 64-22, PG 70-22 and PG 76-22) certified in Arkansas have been selected for this investigation. These asphalt binders from different sources were evaluated in the laboratory to establish a good correlation. These binders have been prepared with different modifiers: styrene-butadiene-styrene (SBS) polymer, PPA, or a combination of both. Multiple Stress Creep and Recovery (MSCR), ER-DSR, Linear Amplitude Sweep (LAS), and Binder Yield Energy Test (BYET) were explored to find their effectiveness. After exploring the DSR-based tests, it can be concluded that the ER-DSR and MSCR tests can be good replacements of elastic recovery test (AASHTO T 301). However, the presence of PPA cannot be identified by following these test methods. Thus, chemical tests such as SARA (Saturate, Aromatic, Resin and Asphaltene) analysis, pH and FTIR (Fourier-transform Infrared spectroscopy) were explored to identify the presence of PPA. The pH measurement test was found to be useful to trace the presence of acid and degree of modification. The SARA analysis was used for observing the changes in chemical fraction due to aging and subsequently useful to predict rutting. On the other hand, spectroscopical analysis (FTIR) was found to be an effective tool to evaluate the change in chemical fingerprint due to aging.
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