Evaluation of the properties and microstructure of SBS and EVA polymer modified bitumen

This paper presents a laboratory study of modified bitumen containing styrene-butadiene-styrene (SBS) and ethylene vinyl acetate (EVA) copolymers. The polymer modified bitumen (PMB) samples have been prepared by means of multi purpose laboratory mixer depending on the type of the polymer. A 50/70 penetration grade base (unmodified) bitumen has been mixed with SBS and EVA polymers at different proportions. The properties and morphology of the samples have been determined and characterized using conventional and empirical test methods and fluorescence microscopy. The mechanical properties of the hot-mix asphalt (HMA) containing SBS and EVA PMBs have also been analyzed and compared with HMA incorporating base bitumen. The results indicated that, the morphology and properties of the modified bitumens, as well as the mechanical properties of polymer modified HMA are dependent on the type of polymer and polymer content. At low polymer contents, the samples revealed the existence of dispersed polymer particles in a continuous bitumen phase, whereas at high polymer contents a continuous polymer phase has been observed. Polymer modification improved the conventional properties of the base bitumen such as; penetration, softening point, temperature susceptibility, etc. It was also concluded that, the mechanical properties of HMA prepared with the SBS PMB samples such as Marshall stability were enhanced with the increasing polymer contents. (C) 2007 Elsevier Ltd. All rights reserved