Rheological studies of performance grade bitumens prepared by blending elastomeric SBS (styrene butadiene styrene) co-polymer in base bitumens
Graphical abstract
Introduction
Bitumen is a mixture of asphaltene, aromatic and naphthenic hydrocarbons. Small quantities of organic acids, bases, and heterocyclic components containing nitrogen, oxygen, sulfur are also present along with some metals e.g. Fe, V, Ni [1]. The use of synthetic polymers to modify the performance of conventional bitumen binder’s dates back to the early 1970, when a decrease of temperature susceptibility, increased cohesion and modified rheological characteristics were observed for these modified bitumen binders [2]. Polymers for such purposes should have a number of requirements [3]. It must be compatible with bitumen and not cause phase separation during storage at high temperature [1], [2], [3], [4]. Styrene butadiene styrene (SBS) is probably the most frequently used polymer in the bitumen modification [1], [5], [6], [7], [8]. SBS itself shows cross-linked elastomeric network behavior [9]. It is usually added in the concentration of 3–6% wt. When mixed with base bitumen, SBS is swollen and disperse throughout the bulk and behaves as cross linker [9], [10], [11], [12]. This cross linkage increases the elasticity, recovery and cohesion of the bitumen. These parameters play vital role in the rheological properties of modified bitumen. SBS copolymers derive their strength and elasticity from physical cross linking and the molecules into a three dimensional network [1], [2], [3], [4], [9], [10], [11]. Extent of polymer modification depends on the nature of base bitumen (feed stock) and subsequently the compatibility of the bitumen-polymer system [11], [12]. SBS is one of the most commonly used polymers to modify the performance of bitumen as it forms high interaction with maltene components [13].
In this paper the modification was carried out by using SBS in the concentration range of 0.5–1.5% wt of base bitumen to prepare performance grade bitumen PG58 and PG64. The comparison of rheological properties of PG58 and PG64 bitumens was done. The variation in different rheological parameters like δ, G*, G*/Sin δ and G′modified bitumen/G′base bitumen, G″modified bitumen/G″base bitumen and G*modified bitumen/G*base bitumen has been studied against temperature.
Section snippets
Materials
Two base bitumens, 60/70 and 80/100 were obtained from Haldia Refinery (Indian Oil Corporation), India and styrene butadiene styrene (SBS) elastomeric copolymer was supplied by DuPont.
Preparation of SBS modified bitumens
Six SBS modified bitumens were prepared at laboratory scale using 500 mL glass assembly. Three different concentrations of SBS copolymer as 0.5% wt, 1.0% wt and 1.5% wt were taken with 60/70 and 80/100 base bitumens each to prepare six modified bitumens. Pre-weighted amount of polymer was added to base bitumens at
Physicochemical properties of base bitumens
The key physicochemical properties of 60/70 and 80/100 base bitumens are mentioned in Table 1. Both the base bitumens have specific gravity in the range of 0.97–1.02 and °API in the range of 7.22–8.59. This indicated that both are aromatic rich. Low colloidal index (CI) and SARA analysis also showed that 60/70 is more aromatic rich (Table 2) and thus may have good potential compatibility with SBS. 60/70 base bitumen is also harder than 80/100 as it has low penetration and high softening point
Conclusions
Improvements in the rheological properties of bitumen have been studied when 0.5, 1.0 and 1.5 SBS % wt is added in to 60/70 and 80/100 base bitumen respectively. Conventional physicochemical characteristics like penetration, softening point, and ductility of bitumen have been determined and correlated. As far as rheological properties are concerned, complex modulus G* increases with addition of SBS and decreases with increase in temperature. In similar manner the value of phase angle δ
Acknowledgements
We kindly acknowledge the Director CSIR-IIP for his kind permission to publish these results. The authors also thank to Mr. Piyush Gupta and Mr. L. N. Shiva Kumar Konathala for carrying out NMR and SEM analysis.
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