Polymer application for the improvement and modification of the bitumen used in roads surfaces has expanded in recent decades. The roads engineers and constructors, therefore, have used the modified bitumen in asphalts helping in this way to increase roads and pavements service life and improving the durability of the roads and asphalts. The bitumen used in asphalt mixture constitutes only a low percentage of the weight of this mixture (between 4% and 6%), but even this small amount has a significant effect on asphalt performance. The polymers that are mostly used in promoting the bitumen specifications are polymer modifiers including: styrenebutadiene-styrene (SBS), as well as similar polymers such as styrene-butadiene-rubber (SBR), ethylene-vinylacetate (EVA) and polyethylene (PE). Polymers as the most important family of bitumen modifiers are added to bitumen to improve bitumen performance and to increase its effectiveness. Among the existing polymers, SBS is considered as the best bitumen modifier. In this research, SBS as one of the elastomer-thermoplast modifiers was added in different weights (2%-5%) to bitumen 60/70 in Isfahan Refinery and its effect on asphalt properties were investigated. Adding this polymer to bitumen improves the Marshall stability of sample asphalt, flow, module of rupture and asphalt content voids. However, it has a minor effect on asphalt special weight. Adding SBS would also lead to asphalt fatigue life.

The weaknesses of the traditional asphalt cements produced by the refineries are the main factors in premature failure of asphalt pavements. One of the measures to prevent these failures is the modification of the asphalt using additives. A variety of materials have been used for modification, among which are polymers and nano materials, including nanoclays. As the effects of these two types have not been compared in the literature, this paper describes the results of an experimental work, in which the effects of a type of nanoclay and Styrene-Butadene-Styrene, SBS, on the properties of 60.70 penetration grade asphalt cement have been investigated. Different amounts of each additive have been added to the asphalt, and the properties of penetration grade, softening point, penetration index, dynamic viscosity, and the rheological properties including phase angle and complex dynamic modulus have been studied. The results show that, both the additives have a stiffening effect on the asphalt, which increase the strength against permanent deformation. However, the stiffening effect is dependent on the type of additive and the amount of them used for modification. The SBS polymer has a better effect for improving the resistance against permanent deformation.

With respect to the physical and mechanical limited qualities of bitumen, it benefits from certain specific ability in application and its life service. Polymers as the most important modifiers of bitumen are applied to it in order to improve its functional efficiency. Among various polymers, styrene-butadiene-styrene (SBS) is the best modifier of the bitumen. In this work, SBS polymer as one of the modifiers of elastomeric thermoplastics with different weight percentages (2% to 5%) have been mixed with bitumen (60.70) of Isfahan Refinary and its effect on different properties of the bitumen for example penetration index, softening point, Frass breaking point and reduction in weight percentage has been studied. Furthermore, in this paper, the modified bitumen property on performance grade is the preferred category. Classification of modified bitumen based on performance grade makes it possible to provide perfect bitumen pattern in different climates.

A key issue to the development of using modified bitumen is the high price of additives, including fibers, which in turn, can increase the cost of bitumen and modified asphalt mixtures. In contrast to other research, in this study, cheap waste materials obtained from paper-making manufacture, including Liquor and cellulose microfibers (obtained from waste pulp mills) are used to improve the properties of modified bitumen while reducing the cost of producing modified bitumen. Further, bitumen modified by styrene-butadiene-styrene (SBS) and styrene-butadiene rubber (SBR) were examined in this study in order to compare with bitumens modified by cellulose microfibers. For this purpose, SHRP tests, including dynamic shear rheometers and bending beam rheometers, were performed on polymer and fiber modified specimens. Based on the results of this study, all modified samples displayed a significant increase in bitumen hardness. Tests of classical bitumen and rotational viscosity demonstrated that polymers of butadiene-styrene-styrene and styrene-butadiene rubber significantly enhanced the viscosity and hardness of bitumen in comparison with other polymers. Consequently, the mix and compaction temperature of the modified samples with these additives have significantly increased. Results revealed that Liquor-containing bitumen improved its high-temperature performance, but it had a negative effect on the bitumen's low-temperature performance. Furthermore, cellulose microfibers had less effect on improving bitumen's properties than polymers such as styrene-butadiene-styrene and styrene-butadiene-rubber. However, cellulose microfibers' capabilities to modify the properties of bitumen, including a lower mixing and compaction temperature of asphalt mixtures than polymers and cheaper production and implementation of asphalt pavements due to the use of cheap waste materials, cannot be overlooked.

Road safety and convenience of driving has been greatly affected by pavement quality; so, it is essential to evaluate the asphalt performance and its common failure such as Fatigue. Nowadays, an increase in frequency of heavy load traffic causes premature fatigue distresses in asphalt pavements which leads to enhancement the costs of road maintenance and repairs. This makes the improvement of the properties of bitumen and asphalt mixtures inevitable. Although the amount of bitumen in asphalt mixtures is not high, it has a significant impact on mixture performance. Styrene-butadiene-styrene is known as one of the most used polymers to improve the properties of asphalt which has led researchers to use alternative materials with the same functional properties due to the lack of sufficient instability in bitumen and its high price. In this study, to find a suitable alternative for this polymer, a mixture of low-cost polymers of styrene-butadiene-rubber and polystyrene has been used with the ratio from 35 to 65 percentage of each combination. In this regard, styrene-butadiene-styrene and polymer blends has been added to the bitumen of the asphalt samples by 3 to 5 percentage. Moreover, 2 percent nanoclay has been mixed inorder to increase the stability of the polymers in bitumen. Thereafter, four-point bending beam and indirect stretch tests has been utilized to evaluate fatigue performance of samples. The results of this research shows that the polymer blends with mentioned composition can be used instead of unstable and expensive traditional SBS, especially when samples have more than 50 percentage styrene-butadiene-rubber in their compositions.

The fuel resistance property plays an important role in asphalts, but available standards for determining this characteristic are presently lacking. In the present work, a number of polymer modified bitumen with styrene-butadiene-styrene (SBS) polymer (4, 5, 6% SBS) and SBS/ sulfur modified bitumen with various percentages of sulfur (1.65, 3, 3.5% based on polymer content) were prepared. Each sample was immersed in the fuel and after 24 hour its weight loss was measured to determine the effect of fuel on them. Results showed that, increase in SBS content caused improvement in physical and rheological properties of bitumen.After adding sulfur to SBS, conventional properties (softening point, penetration, ductility and temperature susceptibility) was improved. Rheological properties were determined by Dynamic Shear Rheometer (DSR). Increase in polymer content and sulfur level led to increase in complex shear modulus (G*) and improvement of the rutting factor. Results indicated that more physical bonds with increase in polymer content and more chemically bonding between polymer, sulfur and bitumen by increasing in sulfur content led to more fuel resistance characteristic.