Effect of storage stability on chemical and rheological properties of polymer-modified asphalt binders for road pavement construction

Polymer modified asphalt binders (PMB) are being commonly used instead of neat binders when superior performance is needed during the road service life. The addition of polymer improves the binder's properties at high, low and mid-range temperatures. However, the effectiveness of polymer modification in improving road performance depends on a chemical-structural modification in the binder's composition to be effective and durable. The phase inversion phenomenon between asphalt components and the added polymer leads the binder to assimilate the polymer characteristics. PMBs can have stability problems and separation; in fact, polymers and bitumen components can lose most of the benefits from the modification due to separation during the storage phase. Common testing for storage stability assessment includes the cigar tuben test (EN 13399, 2010) which provides an indication of whether separation has occurred. To evaluate the effects of separation on performance-related properties of the binder, the present study analyzed the storage stability and separation phenomena of five PMBs by performing an advanced-rheological storage stability test, based on frequency sweep tests on samples taken from the top and bottom part of 3, 5 and 7-day stored cigar tuben specimens. Master curves were developed for newly mixed and several storage conditions and were compared to identify possible separation phenomena between top and bottom samples. Indices were also developed to quantify separation of samples. Results showed that storage stability problems commonly start at the third day of storage. Binders which were seriously affected by separation, seemed to incrementally lose their homogeneity (top and bottom part) between 3 and 7 days. Other binders preserved their rheological characteristics during storage, maintaining equal values between the top and bottom samples. All stored binders were affected by an aging factor.