Effects of Curing Time, Temperature, and Vacuum Pressure on Asphalt Emulsion Residue Recovered by Vacuum Drying Method

This study included five different recovery methods for six emulsions (CRS-2, CRS-2P, CRS-2L, SS-1, SS-1L, and SS-1H) and their corresponding unaged base binders. These five recovery methods consisted of different curing times, temperatures, and vacuum pressures. The goal of this study was to understand the effect of these variables on the rheological properties of the recovered asphalt emulsion residue during the recovery process. Rheological properties such as G*/sin delta, phase angle, and average percent strain recovery were determined to quantify stiffness, oxidative aging, and change in creep recovery due to polymer modification. One new recovery method using a vacuum drying oven was explored in this study. This method reduced the effects of oxidative aging and reduced the recovery time to 6 h. The results show that this newly proposed vacuum drying method ensured better drying of the sample and produced residue that was not unnecessarily aged and was similar to unaged base binder in stiffness, whereas with ASTM D7497 oxidative aging plays a significant role in residue stiffness by almost doubling the stiffness relative to unaged base binder. Also, this 6-h vacuum drying method allowed us to clearly identify the presence of polymer. Overall, this report explains the reasons for the differences between the stiffnesses of unaged base binder and emulsion residue, considering oxidative aging, remaining moisture, emulsifier, and polymer modification.