Viscoelastic characterization of blended binders for asphalt pavement recycling
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The main purpose of this dissertation was to study the SHRP Performance-Graded (PG) binder system for selection of recycling agent for asphalt pavement recycling projects. Traditional asphalt cement testing methods such as viscosity and penetration have several shortcomings and could not characterize the binders at a wide range of temperatures and loading times. The PG system characterizes asphalt cement with cyclic and creep tests in a wide range of temperatures and loading times. The PG system makes it possible to relate the testing parameters with the asphalt pavement distresses such as fatigue, rutting, and low-temperatures cracking. SHRP did not look at the asphalt pavement recycling. Therefore, it was necessary to study the PG binder system for asphalt recycling. One asphalt cement was selected as the binder in the reclaimed asphalt pavement. Two soft asphalt cements and two recycling agents were selected as the rejuvenator. The original binder was aged in the laboratory and was blended with rejuvenated materials. The resultant 10 blended binders were characterized with a Dynamic Shear Rheometer and a Bending Beam Rheometer apparatus. The testing procedure used involved performing sweep temperatures ranging from -30 to 70°C. The PG testing results were used to develop some models for characterization of blended binders. The proposed models are based on PG binder testing parameters such as complex shear modulus (G*), phase Angle (δ), stiffness (S), and m-value. The analysis showed that a linear relationship is accurate enough for prediction of PG binder parameters with a proportion of recycling agents. The temperature dependency of blended lines for complex shear modulus, stiffness, phase angle and m-value was studied. The loading time dependency of blended binders was studied by building the master curves. The SHRP A-002A binder model was used for estimating the rheological indexes (R) and crossover frequencies (ωc) of blended binders. The regression analysis showed that a linear relationship is accurate enough for prediction of SHRP A-002A parameters with a proportion of recycling agents of blended binders. The temperature dependency of shift factors was studied with defining temperature, Td, from WLF Equation.