Establishing Particle Size Recommendations for Cationic Asphalt Emulsions

Asphalt emulsions are used in flexible pavement maintenance and rehabilitation treatments. Emulsion specifications for material characterization are based on testing methodology dating to the 1930s. Newer test methods, including particle size analysis (PSA) of binder droplets in emulsion, have been explored but not implemented into specifications. The objective of this study is to observe the particle size and performance of cationic slow-setting (CSS) emulsions and establish baseline particle size recommendations for cationic emulsions. Four physical property tests (residue, oversize particles, viscosity, and particle size) and two cold mix asphalt performance tests (indirect tensile strength (IDT) and direct shear test (DST)) were conducted on two emulsions (CSS-1 and CSS-1H) over a six-month period. The physical properties of both emulsions were acceptable, and median particle size of the CSS-1H was approximately 3 microns larger than the CSS-1. The IDT strength and DST shear strength of the CSS-1H were higher than of the CSS-1. Recommendations for particle size were proposed by defining maximum limits on median, d10, d90, and span. It is recommended that the maximum median (d50) size of CSS emulsions is 6.0 microns. Future research is needed to standardize PSA procedures, assess recommendations for a wider range of emulsions, and evaluate applicability of minimum particle size limits.