Effect of High-Density Polyethylene Pyro-Oil Modification on Chemical, Rheological, and Damping Properties of Binders

Plastic waste is harmful to the environment and takes thousands of years to decompose naturally. Pyrolysis is an effective method of plastic waste management, and the oil obtained from the process can be used as a modifier for bituminous binders. The polymer modification of bitumen is an effective and commonly used method for improving the rheological performance of the binders. The mixing temperatures are considerably elevated after the addition of polymers to the binders. Various pyrolytic oils are used to reduce the mixing and compaction temperatures of the polymer-modified binders (PMBs). This study analyzed the effect of the addition of high-density polyethelene (HDPE) pyro-oil in viscosity graded (VG30), styrene-butadiene-styrene (SBS), and ethylene vinyl acetate (EVA)-modified binders on the mixing temperatures and rheological properties. The concept of rheograms and Carreau–Yasuda (CY) model fitting were used to determine the mixing temperatures. The rheological investigation involved frequency sweep, temperature sweep, steady shear test, and multiple stress creep and recovery tests using a dynamic shear rheometer. The variation of black diagrams was studied for the binders along with the variation in phase angle and complex modulus of the binders. Fourier-transform infrared spectroscopy was used to assess the chemical changes after the modification and aging of the binders. Damping energy characteristics were investigated for the unmodified, polymer-modified, and HDPE pyro-oil–modified bituminous binders. With increasing shear rates from 100 to $\mathrm{10,000}{\mathrm{s}}^{-1}$, the mixing temperatures of the modified binders decreased by about 8°C–16°C. The addition of pyro-oil to the base and polymer-modified binders decreased the percentage rate of increase in carbonyl and sulfoxide indexes, in turn increasing the resistance to aging of the binders. The addition of pyro-oil reduced the mixing temperatures of base and SBS-modified binders, and the rutting performance of SBS-modified binders. This reduction in mixing temperatures and aging will lead to less energy consumption at the mixing plants, and longer service life of pavements.

The use of HDPE plastic waste in the form of pyro-oil in flexible pavements will help reduce the amount of plastic waste. The modification of bitumen with pyro-oil will decrease the amount of bitumen used in pavement construction, ultimately reducing the use of nonrenewable crude reserves that are depleting rapidly. The concept of rheograms for evaluating the flow behavior of the modified binders suggested in this study and its application in mixing plants will be beneficial in reducing mixing temperatures at higher shear rates. The use of pyro-oil for the modification of polymer-modified binders will lead to a reduction of mixing temperatures. This will help save energy at the plants. The application of pyro-oil along with polymers will produce aging-resistant, rutting-resistant, and damping-resistant binders, which will lead to stronger and durable pavements for longer service periods. Hence, the analysis in this research will be beneficial for researchers, highway engineers, hot-mix plant owners, pavement designers, and consultants.