Volume 8, Issue 10 (November 2011)
Application of Rheological Models to Modified Roofing Asphalts
The increased understanding of material behavior with rheology has existed for approximately 80 years as a science and has been applied to roofing products for over 50 years. With asphalt binders, several techniques exist for understanding rheology via the use of models. One of the best recognized models for the evaluation of the rheology of unmodified asphalt binders is the Christensen-Anderson model, and various developments of that model have occurred, enabling its use with filled systems such as those used in roofing applications. In addition to this model, the Rowe-Baumgardner-Sharrock model (developed by the authors) is introduced as an alternate method for defining the properties of roofing products that exhibit visco-elastic solid properties. When rheological data are fitted to master curve functional forms, changes in the model parameters can be rapidly visualized. The performance of various products can be assessed using this technique and can be related to the rheological parameters developed from this model (for example, the rheological index, crossover frequency, etc.). An analysis of the data is presented that includes testing using various rheometers over a wide range of temperatures. These data have been combined into a single master curve and plotted in various formats. The data show how the rheological index and the crossover frequency of the materials change over time, particularly with aging. Performance products can then be assessed and evaluated from both the historical data and models that enable the prediction of cracking and deformation. Adiscussion of the key parameters and a trend analysis are shown. Furthermore, the analysis is applied toward understanding the effectiveness of polymer networks in the roofing materials. As materials age, their properties change, and this can be observed, allowing the study of the effects of polymer network degradation with aging. This paper offers some further understanding of how key rheological parameters change.