Laboratory Performance of Polymer-Modified Asphalt Binders and Mixtures at Low Temperature

A research study was undertaken to investigate the impact of Vinyl Acetate Ethylene (VAE) copolymer as an asphalt binder modifier with and without combination with Styrene-Butadiene-Styrene (SBS) copolymer. SBS has been used for decades to enhance asphalt binder performance, but the use of VAE as an asphalt modifier is not that old. The overall goal of this project was to determine the level of improvement achieved in the engineering properties of asphalt binder and mixture at low temperatures (well below freezing temperatures) due to incorporation of VAE/SBS copolymers. Low-temperature rheological properties of the modified binders as well as low-temperature resistance of the corresponding asphalt concrete mixtures were evaluated. Three different types of VAE and one type of SBS were used and blended at different levels into the base neat binder along with the designated dosages of VAE. Polymer modification was carried out in the lab such that the total modifier content (SBS plus VAE) would be 4.5% of the mass of the binder blend. The neat base binder used in this study was a PG 64-22. There was no change in the binder nominal low-temperature grade due to the VAE modifications, but the binders modified with higher VAE content exhibited an improvement because of lower stress sensitivity. The results also suggested that an advantage of replacing a portion of SBS with VAE could be notably recognized at the low temperatures in terms of stress relaxation. Replacing part of SBS with VAE, at 25% or more of the total modifier, expedited stress relaxation (i.e., resulted in higher m-value from Bending Beam Rheometer). Indirect tensile strength (IDT) was conducted at − 20 and − 10 °C to evaluate the cracking potential of the VAE-SBS polymer-modified asphalt mixtures at low temperatures. The results indicated that while a significant difference did not exist in the indirect tensile strength of the polymer-modified mixes versus the control mix, there was an improvement with respect to fracture toughness of the VAE-modified asphalt mixtures. This finding is in line with the results from the binder characterization, indicating improved resistance to low-temperature cracking due to usage of VAE.