Mechanism of Crumb Rubber Modifier Dissolution into Asphalt Matrix and Its Effect on Final Physical Properties of Crumb Rubber-Modified Binder

Modification of asphalt by crumb rubber modifier (CRM) is mostly done through exchange of components between asphalt and CRM. At 160 degrees C and 10 Hz, CRM absorbs aromatics of asphalt and swells; however, at 220 degrees C and 50 Hz, CRM dissolves into the asphalt; this process leads to the release of different components of CRM including carbon black, fillers, and polymeric and oily components. Depending on interaction conditions, CRM dissolution is performed differently, and therefore the state and role of the released components can be different. In this research different mechanisms of dissolution of one size of CRM in asphalt matrix and their effects on property development of modified asphalt were studied by using different analytic techniques, including dissolution test, dynamic shear rheometer (DSR), thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) spectroscopy. Dissolution test results in combination with DSR results indicate the state and the role of CRM particles in the matrix, while TGA and FTIR spectroscopy show the type and amount of released components from CRM. The results reveal that for the materials used in this study interaction temperature is the main factor affecting the mechanism of dissolution of the CRM particles and consequently defines the role of the released components of CRM in asphalt matrix. DSR results indicate that during interactions at 190 degrees C (intermediate interaction temperature), released components are more effective on physical properties of asphalt than are released components during interactions at 220 degrees C (high interaction temperature).