Effects of Curing and Oxidative Aging on Raveling in Emulsion Chip Seals

Abstract

Although chip seals have a proven history of performance, several distresses are commonly encountered in the field. The most common distresses in chip seals are flushing or bleeding and aggregate loss from the top layer (i.e., raveling). Raveling is not restricted to the early life of the chip seal, but continue throughout the service life. The current state of knowledge and testing of the mechanisms governing raveling in chip seals does not sufficiently account for the effects of in-service emulsion–aggregate bond maturation and oxidative aging on chip loss over the expected service life of the chip seal. Emulsion–aggregate adhesion was thought to control the early raveling process, while the residual asphalt binder rheological properties and aggregate embedment in the emulsion might contribute to later raveling in chip seals. Raveling of chip seals subjected to varying degrees of time–temperature conditioning was evaluated to account for different chemical and physical interactions at the aggregate–asphalt interface. Testing results showed that the rate of in-service raveling depended on the curing process and subsequent in-service oxidative aging as the adhesive and cohesive forces at the emulsion–aggregate interface changed. The initial bond maturation resulted in a decreased rate of chip loss, and the in-service oxidative aging of the asphalt emulsion led to a higher aggregate loss as a result of the emulsion's strain intolerance and inability to relax stresses induced by traffic.