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Styrene-butadiene-styrene (SBS) polymer is one of the most preferred additives to improve performance in hot mix asphalt pavements. The storage instability, in other words, the separation of a polymer-rich phase from the bitumen-rich phase in the course of storage and transportation is one of the prevalent problems in SBS modified bitumen. The present study attempted to obtain modified bitumen at the same performance level with the SBS modified bitumen, but stable with respect to the storage stability. For this purpose, both SBS and American Gilsonite (AG) were used in modified bitumen production. It was determined that modified bitumen at the same performance level was obtained with the use of 5 % SBS or 18 % AG in bitumen modification. It was also determined that the performance levels of the modified bitumen obtained with the use of 2 % SBS + 13 % AG, 3 % SBS + 10 % AG and 4 % SBS + 6 % AG were similar. Additionally, 2 %, 3 % and 4 % SBS modified bitumen were used for the assessment of storage stability properties of the SBS modified binders. These 8 different modified bitumen samples were tested for storage stability based on the EN 13399 standard. Penetration, softening point, rotational viscometer, bending beam rheometer, and dynamic shear rheometer tests were conducted on the samples. Based on all conducted tests, it was determined that more stable binders were obtained with the use of AG and SBS in terms of storage stability compared to solely SBS modified bitumen.

In this study, the volumetric properties, Marshall stabilities, the indirect tensile stiffness moduli, and the fatigue and permanent deformation strengths of hot mix asphalts prepared with the same performance grade binders in accordance with Superpave method at optimum binder contents were comparatively investigated. In addition, the effect of bitumen modification using SBS on the mechanical characteristics of the mixtures was evaluated. Dynamic creep and indirect tensile fatigue tests were conducted at two distinct stress levels and three different loading periods. As the binder tests, it was determined that the modified bitumen obtained by adding of 3% SBS by weight into the B 160/220 binder yielded the same level of performance with the B 70/100 bitumen. It was also found that using 3% SBS by weight for the purpose of bitumen modification enhanced the desired properties of the mixture to a significant degree. It was observed that the best performance belonged to the mixtures containing B 70/100 bitumen, while the worst performance was found for the mixtures made from B 160/220 bitumen. Additionally, although the mixtures prepared by the same performance grade binders in accordance with the Superpave system were expected to behave similarly, it was found that they differed considerably with respect to their stiffness, tensile strength and strength against permanent deformation.

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