INVESTIGATING PROPERTY DETERIORATION IN SBS MODIFIED BINDER AND MIXTURE DURING STORAGE

Abstract

Polymer modified binder (PMAs) enhance the performance of bituminous roads over a wide range of traffic and environmental conditions. Roads constructed using PMAs have a longer service life and lower maintenance requirements. Styrene-butadiene-styrene (SBS) is one of the most widely used polymers for binder modification since the combination of styrene and butadiene segments offers excellent stiffness and elastic recovery characteristics. Although SBS offers excellent performance properties for the binder, it has limited thermal and oxidative stability. This drawback becomes significant when SBS modified binders are exposed to elevated temperatures (180 °C to 200 °C) during storage and transportation in closed metal containers. To mimic the storage conditions, we have carried out the laboratory investigation by storing the PMA samples in laboratory ovens in closed tubes and containers. This comprehensive study was carried out considering many parameters such as storage temperature, storage time, SBS concentration, SBS type, base binder, and additives. Our investigation reveals significant property deterioration in SBS modified binder during storage, and the extent of decline strongly depends on SBS concentration and storage temperature. Asphalt mix performance was also evaluated to understand the effect of property deterioration in SBS modified binders on bituminous pavements. We report a comprehensive study on the effect of storage temperature, SBS concentration, and base binder on polymer modified binder properties during storage at elevated temperatures in sealed aluminum tubes. Our results show that storage temperature and SBS concentration play a significant role in the observed property erosion, while the type of base binder has a lesser effect. The samples were stored in sealed aluminum tubes at 150 °C, 180 °C, and 210 °C for up to 21 days. At 150 °C, the properties of PMAs remained intact even after storing for 21 days. But, significant erosion in conventional and rheological properties of SBS modified binder takes place within the first 3 days of storage at temperatures ≥ 180 °C. At 210 °C, the PMA properties degrade to the base binder values within 1 day. Gel permeation chromatography and rheological results clearly show the degradation of SBS molecules. The property loss is most significant when the SBS concentration is between 3% and 6%, in the steep middle region of the S-curve (softening point vs. polymer concentration). Among PMAs with different base binders, noticeable differences were observed only when the SBS concentration was in the steep middle region of the S-curve (3–6%). We have discussed all the results in the background of the S-curve, thereby highlighting the major role played by SBS concentration in property erosion during storage.