A Study to Evaluate the Effects of SBS Polymer Modification on the True Grade of an Asphalt Binder

Polymers are currently added to asphalt to increase characteristics that essentially improve the life of the asphalt. One polymer commonly added to asphalt is Styrene-butadiene-styrene (SBS). This polymer is common due to its elastic properties that increase viscosity, elastic response, and complex modulus. Although this is known, the current PG grading system may not adequately show the attributes of polymer modified asphalt. Historically, additional tests, known as PG Plus tests, have been performed on polymer modified asphalt (PMB) to ensure the asphalt has been modified to the end user specification. The new multiple stress creep and recovery (MSCR) test has been proposed to eliminate the proliferation of plus specifications throughout the states. The current performance grading specification, AASHTO M320, and the elastic recovery test were compared to the new MSCR grading specification, AASHTO MP-19, to ascertain a more appropriate grading system. This will be studied by taking in-house polymer modified binders that were developed and verified to have achieved full interlocking by use of fluorescence microscopy and measuring the mechanical properties of the in-house polymer modified binders to obtain the continuous grade of the binders. The addition of polymers increased the rheological properties and high grades of the base binder, as well as increasing the traffic grades of the proposed MP 19 specification. Although, the low PG grade was not changed, the continuous grading system showed that addition of polymer did, in fact, change the low-temperature properties of the binder.