CHEMICAL AND RHEOLOGICAL EVALUATION OF AGING PROPERTIES OF SBS POLYMER-MODIFIED BITUMENS

The ageing properties of Styrene-Butadiene-Styrene (SBS) polymer modif ied bitumens were evaluated using Dynamic Mechanical Analysis (DMA), G el Permeation Chromatography (GPC) and Fourier Transform InfraRed (FTI R) spectroscopy. The binders were aged by means of the Thin Film Oven Test (TFOT) and the Rolling Thin Film Oven Test (RTFOT), respectively. It was observed that ageing resulted in degradation of the SBS polyme r (decrease in the polymer molecular weight) and oxidation of the bitu men (increase in the content of polar oxygen-containing molecules and increase in bitumen molecular weight). The polymer was observed to res ist formation of sulphoxides. Changes in the rheological properties of aged-modified binders were dependent on a combined effect of bitumen oxidation and polymer degradation, which varied with bitumen source/gr ade and polymer type/content. In all cases, the aged modified binders showed better rheological properties than aged base bitumens. The stud y also indicated that the ageing index obtained using DMA was largely influenced by temperature and frequency. This parameter may be applied for evaluating the base bitumens and modified binders with a low poly mer content (3% in this study), but not for modified binders with a hi gh (6%) polymer content. (C) 1998 Elsevier Science Ltd. All rights res erved.