Rheological Behavior of Emulsion Residues Produced by Evaporative Recovery Method

The increasing use of surface treatments has generated a need for the development of specifications and test methods for performance of construction and in-service properties of emulsions. A major impediment in characterizing emulsion is the establishment of a generally accepted residue recovery method. ASTM recently approved a procedure for a low-temperature evaporative recovery method. It involves consecutive 24-h curing periods at 25°C and 60°C in a forced-draft oven. Initial rheological evaluation of emulsion residues indicates that residue properties far exceed those of the unaged base binder and are closer to those of aged materials. Also, concerns have been expressed about the length of this procedure and the possibility for reducing the time required. This study focused on evaluating whether the full 48-h curing period is required and identifying the cause of different behaviors relative to base binders. Evaluation was conducted at high and intermediate temperatures on emulsion residues and base binders subjected to different aging conditions, with the dynamic shear rheometer. The study included neat and polymer-modified base asphalts, and latex, polymer-modified, and conventional cationic rapid set emulsions. Results indicate that oxidative aging contributes significantly to the change in rheology with time of curing, compared with unaged base binder. Especially for modified emulsions, the full 48-h curing period is needed for full development of rheological properties. However, the properties should be compared with short-term aged binders rather than unaged binders. Results support the ASTM method but suggest that residue be considered rolling thin-film oven-aged material rather than unaged material.