Rheological Characterization of Blended Paving Asphalt

ABSTRACT Asphalt is processed in India through various means such as straight-run, air blown and blending. Production of asphalt for paving purposes in some of the refineries is carried out by blending the heavy extract with the PDA pitch. Since 60/70 or 80/100 penetration grade is predominantly used in India, appropriate proportions of PDA pitch and extract are determined to meet the penetration grade. Considering the current move in India towards viscosity grading and then to performance grading, a need was felt to observe the rheological properties of blended asphalt and the role of blending process on the final end product. This investigation reports the rheological characterization of various blends made with PDA pitch and heavy extract. Three blend proportions were manufactured by two different blending process and all the blends were subjected to short term aging in rolling thin film oven. The unaged and short term aged blends were tested for steady shear, creep and recovery and stress relaxation properties. The single point measurement of viscosity at a specific temperature cannot reveal the complex behaviour of asphalt. A complete and systematic rheological characterization is necessary. In fact, this investigation reports for the first time, stress overshoot in steady shear and measurement of first normal stress difference relaxation for blended asphalt. From the analysis of the experimental data it is shown that blends with higher proportion of PDA pitch are more temperature susceptible and the blending process tends to “homogenize” the mixture. One can use the data gathered from these experiments for designing asphalt blend with the required appropriate property. These experiments also underline the requirement to develop non-linear constitutive models for asphalt and asphalt blends.