Effects of paraffin on low temperature properties of SBS modified binder

The method applied most to improve engineering properties of bituminous hot mixtures which are used in coating layer is the enhancement of bitumen’s properties with various additive materials. Polymer based additive materials are generally used for bitumen modification. Among these additive materials, styrene-butadiene-styrene (SBS) block copolymers are mostly used. It was determined that SBS increases the resistance of mixtures against to rutting and fatigue at high temperatures. However it was determined that increased content of SBS caused both worsening of the low service temperature and also workability of the mixtures. It is reported that a rubbery network is created which improves elastic response and enhance low temperature cracking resistance in case the SBS-rich phase forms. It is known that using paraffin’s property of reducing viscosity and increasing softening point together with SBS modification which causes increase in viscosity, enhances this combined binder’s properties of high temperatures and workability; however there exists no study related to the behavior of this combined binder at low temperatures, in literature. In this study the effect of SBS and paraffin modification on base bitumen were investigated. Firstly the bitumen modified individually with SBS and paraffin was evaluated in terms of Bending Beam Rheometer (BBR) test. Then, the bitumen including both SBS and paraffin in different contents was tested. Including the three different SBS and paraffin content and also base bitumen, totally 16 different combination were evaluated. In conclusion, it was determined that the ratio of stiffness to m-value gives better result in evaluation of low temperature behavior. At low temperatures, it was determined that stiffness increase with increasing additive rates; however this increase is much more in paraffin modification, in particular, SBS addition at low ratio decreases the increase of stiffness caused by paraffin modification.

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