Uniformity of Unmodified Asphalt Binders in Large Storage Tanks

A prime concern in regard to the storage of asphalt binder in storage tanks is that material allowed to stand in a tank will begin to stratify. This stratification could cause the material to not be homogeneous throughout the tank. If the material is not homogeneous or if the material changes in the storage tank, the Performance Grading (PG) grade of the material would then be in question. Asphalt binder suppliers throughout the Northeast were asked to provide several samples of asphalt binder. These samples were drawn off of a storage tank that contained a neat asphalt binder. This study examined neat asphalts only. The goal was to get samples that represented the tank when it was full, two-thirds full, one-third full and nearly empty. The samples were taken from tanks that would take at least 1 week to empty. The rationale behind this was that if stratification were to occur, this would allow enough time for the material to stratify. The samples were sent to the Connecticut Advanced Pavement Lab for American Association of State Highway and Transportation Officials (AASHTO) MP-1 testing. The samples were tested so that trends in the data could be analyzed regarding changes to the material in the tank. The results of the testing indicate that the unmodified asphalt stored in the suppliers’ tanks appears to remain homogeneous as the level of binder in the tanks is drawn down. The results obtained were within the published AASHTO precision and bias values for each type of testing.