Detection of Polymers in Asphalt Binders

Superpave^TM performance-graded asphalt binder technology continues to advance with some producers focusing on the use of additives to enhance the performance of asphalt binders. A common practice is to modify an asphalt binder with a polymer to extend the high- and low-temperature range. However, agencies require a method to verify the presence of the polymer. The method that is presented serves to demonstrate that gel-permeation chromatographic (GPC) can be used to detect the presence of polymers in asphalt binders. Typically, the polymers used in asphalt binders have a number average molecular weight ranging from 300 to 600 times larger than the number average molecular weight of asphalt binders. The GPC technique separates the polymer from the asphalt binder as a function of molecular size. The analysis of eight unknown samples, some of which were reported to contain a polymer, was conducted. The GPC results demonstrated that three of the asphalt binders were polymer modified while the remaining five asphalt binders were not modified. After the results were reported, the actual composition of the asphalt binders was revealed and found to be in agreement. Thus, GPC can be used as a simple screening test to identify when asphalt binder has been modified with a polymer.