Influence of thermo-oxidative aging on chemical composition and physical properties of polymer modified bitumens

This paper presents some experimental results on property changes due to thermo-oxidative aging of bitumen modified by styrene-butadiene-styrene (SBS) and ethylene vinyl acetate (EVA) copolymer incorporated at various concentrations, i.e. 3, 5 and 7 wt.%. The chemical compositions, the properties and the morphology of the samples have been determined and characterized using SARA (saturates, aromatics, resins and asphaltenes) analysis, conventional test methods and optical microscopy, respectively. The study reveals that polymer modification globally improves the conventional properties of the base bitumen as evidenced by a decrease in penetrability, an increase in softening point and a reduction in temperature susceptibility inducing a rubbery elastic behavior to the base bitumen. This effect is dependent on both the type and the content of polymer used. Moreover, samples prepared with SBS show better improvement as compared with EVA modified bitumens. The morphological analysis shows that there is a clear difference between the SBS and EVA modified bitumens. For 3 wt.% SBS modified bitumens, the polymer phase is homogenously dispersed in a continuous bituminous matrix consisting of polymer particles swollen by the solvating phase of the bitumen. In the case of EVA modified bitumen with the same polymer content, much finer dispersion of EVA particles is observed. After thermo-oxidative aging, the results clearly indicate a hardening of samples, being more pronounced for the base bitumen and those modified with EVA. For all samples, aging reduces the content of aromatics and at the same time increases the contents of resins and asphaltenes, while changes in the content of saturates are almost negligible. These structural modifications may result from oxidation of the bitumen and some chemical interactions with the polymers. (C) 2011 Elsevier Ltd. All rights reserved.