Variable-Temperature Raman Spectroscopy Study of the Phase Transition Mechanism in Asphalt Binders

Tobetter understand the mechanism of precipitation and dissolutionof the crystalline wax in asphalt, it is necessary to investigatethe phase transition process of asphalt at different temperatures.Variable-temperature Raman spectroscopy has been employed to analyzethe phase transition properties of eight asphalt binders from theSHRP material reference library. More abundant Raman spectral structureinformation is obtained by introducing silver nanoparticle colloids(Ag NPs) as a surface-enhanced Raman scattering (SERS) substrate toquench the self-fluorescence. The findings show that Raman spectroscopycan effectively identify different aging states of asphalt accordingto characteristic peaks. In the temperature range of 20-100 & DEG;C, three areas of the Raman spectrum, including 500-1200,1300-1800, and 2500-3000 cm(-1), indicatethat the asphalt has transformed from an ordered phase to a disorderedphase and to a liquid phase. The order parameters are selected torepresent the change of ordered and disordered structures in asphalt.The phase transition occurs mainly from the changes in the intensityand frequency of the Raman crest related to the crystal structureand distorted conformation. The temperature range of phase transitionsfrom an ordered to a disordered range of asphalt has an obvious correlationwith the wax melting point of asphalt, and the disorder degree andmolecular defects of asphalt are also positively correlated with thewax content in asphalt.