Low-Temperature Vacuum Drying Procedure for Rapid Asphalt Emulsion Residue Recovery

Abstract

Asphalt emulsions are used extensively in tack coats and preservation surface treatments. The current specifications for asphalt emulsion residue recovery in AASHTO PP 72 are based on low-temperature evaporative drying. The shortest residue recovery procedure included in AASHTO PP 72 requires 6 h of conditioning in an oven to dry an emulsion. The ability to recover emulsion residues efficiently is of great interest given the ongoing efforts to develop emulsion performance-graded specifications based on residual binder properties. In this study, a rapid, vacuum drying technology was evaluated for asphalt emulsion residue recovery. The procedure enables the recovery of sufficient residual binder for dynamic shear rheometer (DSR) testing within 20–40 min. Five emulsions of different classifications were evaluated using both the vacuum drying procedure and the AASHTO PP 72 procedures. The vacuum drying procedure leads to similar water loss to the AASHTO PP 72 procedures. Based on the temperature-frequency sweep and multiple stress creep and recovery (MSCR) test results, the vacuum-dried residues are softer and more viscous than residues recovered using the AASHTO PP 72 procedures. Fourier transform infrared spectroscopy (FTIR) was performed to identify if oxidation levels could explain the observed in rheological trends. However, the results suggest no clear trend in the oxidation levels of residues recovered using AASHTO PP 72 compared with the rapid vacuum procedure. Future work is necessary to infer which method best reflects residual binders placed in the field.