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Polymers are commonly used to modify asphalt binder in order to satisfy the performance-grade binder's rheological properties, such as shear, storage, loss, and bending stiffness. However, it is not known what types and percentages of polymers affect these properties under conditions of aging. To this end, base asphalt binders were modified with styrene-butadiene and styrene-butadiene-styrene polymers at 3, 4, and 5% and then aged in the laboratory using a rolling thin film oven for short-term aging, a pressure aging vessel for long-term aging, and a draft oven for intermediate aging. The stiffness properties of the modified binders were determined using dynamic shear rheometer (DSR), multiple-stress creep recovery (MSCR), Brookfield rotational viscometer (RV), and bending beam rheometer (BBR) tests. Comparison of aging indexes for storage and loss modulus indicated that aging increases the elastic or storage component more than the viscous or loss component of the complex shear modulus. It was shown that increasing the percentage of polymer results in a decrease in aging for both SB- and SBS-modified binders. Those modified with SB are more resistant to aging than are those modified with SBS. [ABSTRACT FROM AUTHOR]