Study on Frequency Dependency of Sol-Gel Transition of Asphalt

One important factor related to the asphalt pavement performance is the transitory nature of asphalt. Heating asphalt from – 40 to 150 °C, one can observe the transition from glassy solid to viscoelastic solid, viscoelastic solid to viscoelastic fluid and finally to Newtonian fluid. This study focuses on capturing the viscoelastic solid-fluid transition. Specifically, this transition was captured here by the storage modulus (G') and loss modulus (G") cross-over when the sample is subjected to a temperature sweep with constant strain amplitude and frequency. Since this measure depends on frequency of testing, this study also quantifies the influence of frequency. Two types of asphalt of the same grade but manufactured by different process (blending and air blowing) were tested at unaged, short-term aged and long-term aged conditions. The G'-G" cross-over point changes at low frequency and the frequency dependency vanishes above 40 Hz. This frequency independent G'-G" cross-over temperature can then be truly called as the viscoelastic transition temperature or sol-gel transition temperature. It was interesting to note that the aging conditions did not alter the frequency dependency. Also there was no significant difference in cross-over temperature of blended and air blown asphalt.