Viscoelastic transition of unaged and aged asphalt

This investigation reports the viscoelastic solid to fluid transition of asphalt as the temperature is varied. Air blown, blended asphalt and pitch obtained from Arab mix crude were tested under unaged, short-term aged, and long-term aged conditions. All the materials were subjected to two experimental protocols in the 20-50°C temperature region. In the first experimental protocol, the material was subjected to frequency sweep in small amplitude oscillatory shear and in the second protocol the material was subjected to large deformation stress relaxation. From the analysis of the experimental results, it was seen that asphalt exhibited a viscoelastic solid regime, a viscoelastic fluid regime, and a transition regime in the temperature range tested. In the small amplitude oscillatory shear, the transition regime was captured using a frequency-dependent storage modulus (G′)-loss modulus (G'') crossover. In the stress relaxation experiments, the material exhibited three distinct slopes and the transition temperatures were identical with what was seen for frequency sweep experiments. The transition regime for blended and air blown asphalt varied from 15-35°C and the transition temperatures shifted to higher values as the material aged. The variation of damping energy and the failure of time temperature superposition principle also confirmed the transition from viscoelastic solid to viscoelastic fluid behavior in such temperature regions. © 2013 American Society of Civil Engineers.