Rheological performance evaluation of asphalt modified with bio-based polymers

Fuel-based polymers, used as modifiers and additives in asphalt cement binders, improve the rheological performance of the base asphalt binders, therefore increase the resistance to pavement distresses. However, demand for polymers that are biodegradable, environmentally friendly, and cost effective is increasing. Soybean oil used as an alternative in place of soft and rubbery elastomers polybutadiene derived from crude oil was synthesized to bio-based polymers via chemical synthesis methods reversible addition-fragmentation chain transfer (RAFT) and atom transfer radical polymerization (ATRP).\nIn this study, bio-based polymers (PS-PAESO and PS-PAESO-Cl) with different styrene parameters were blended at a dosage of 3% by weight to a base asphalt binder by the solvent blending approach and three different shear blending methods. The objective of this study was to characterize the rheological properties of bio-based polymer modified asphalt blends by conducting dynamic shear rheometer (DSR), rolling thin film oven (RTFO), pressurized aging vessel (PAV), and bending beam rheometer (BBR) based on the Superpave performance graded asphalt binder specifications. The complex modulus (G*), phase angle (δ), mass losses, creep stiffness were determined to evaluate the rheological properties of the modified blends. Statistical analysis was conducted to evaluate the related factors that may influence the test results and to develop statistical modeling for predicting the bio-based polymers with appropriate styrene parameters that would optimize the rheological performance of the modified blends.\nResults from high temperature performance tests show that the addition of bio-based polymer (PS-PAESO and PS-PAESO-PS) used in this study increase the critical high temperature of the base binder that indicate an improvement on the resistance of rutting at high temperature. The similar results are observed from the master curves and the black diagrams which both exhibit stiffer behavior of the base asphalt at higher temperatures after modification, which indicates a rubber-elastic network establishment within the blends. Whereas, these bio-based polymers do not substantially improve the resistance to low temperature thermal cracking based on the critical low temperature results. Another finding is the use of bio-based polymers generally widened the continuous performance grade range of the base asphalt binder, which indicates that the bio-based polymers reduce the temperature susceptibility of the base asphalt binder. Furthermore, the statistical analysis on laboratory test results show no statistically significant difference between the three shear blending methods used in this study and no statistically significant difference between the polymer synthesis reaction durations. However, further statistical analysis by using block design on the shear blending methods and the polymer reaction durations shows there is statistically significant difference between the short and long reaction durations but no statistically significant difference between the shear blending methods. The finalized prediction models based on the response surface modeling present the same predicated styrene parameters in polymer to the test result analysis, which indicates that bio-based polymer with styrene parameters as lower molecular weight and lower styrene content are recommended for achieving higher critical high temperatures.