Aggregate Retention in Chip Seal

Chip seal is a widely used preventive maintenance treatment for flexible pavements. However, a major problem with chip seal is the damage caused by loose aggregates from newly placed seals, partly because of a lack of compatibility between aggregate and asphalt emulsion. In this study, limestone, crushed gravel, synthetic lightweight aggregates, and recycled asphalt pavement materials were studied in the laboratory with two polymer-modified asphalt emulsions to find the aggregate–emulsion combination that would result in maximum chip retention. Replicate specimens were tested in the ASTM D7000 sweep test for each aggregate–emulsion combination. Lightweight aggregates and gravel were also tested in a newly developed test setup for simulating the sweep test. Test results show that lightweight aggregates perform better than gravel. However, lightweight aggregate sources play an important role in chip retention. Emulsion is the most significant factor that affects chip loss. Statistical analysis identified the influential design factors affecting chip retention. Analysis of variance shows that aggregate and emulsion types and aggregate–emulsion interaction are significant factors affecting chip retention. Aggregate precoating and its interaction with emulsion type are insignificant factors as far as chip retention is concerned.