BACKGROUND: Emulsion-based chip seals are the most commonly used chip seal type in the United States; they are frequently used as pavement preservation treatments on flexible pavements. Their primary purpose is to seal fine cracks in the underlying pavement's surface and prevent water intrusion into the base and subgrade. Because chip seals are not expected to provide additional structural capacity to the pavement, benefits ideally are accrued by their application early in a pavement's life before a great degree of distress is exhibited. Although a large body of research is available on chip-seal design practices (as documented in NCHRP Synthesis 342: Chip Seal Best Practices), chip-seal design in the United States remains empirical in nature--based on experience and judgment. Chip-seal design processes that consider the surface condition of existing pavement, traffic volume, environment, and other relevant factors in determining the characteristics and applications rates of aggregates and binder have not been widely used in the United States.
In spite of their apparent benefits, the use of chip seals for pavement preservation in the United States is hampered by the lack of nationally accepted guidance on their design and construction and appropriate specifications and testing procedures for constituent materials. Research is needed to identify the factors that influence chip-seal design and performance and to develop a manual that documents design and construction practices and delineates necessary testing and specifications. Such a manual will provide highway agencies with the information necessary for designing and constructing long-lasting chip seals and preserving pavements.
OBJECTIVE: The objective of this research was to develop a Manual for the Design and Construction of Emulsion-Based Chip Seals for Pavement Preservation in a format suitable for consideration and adoption by the American Association of State Highway and Transportation Officials (AASHTO). The research was limited to the application of chip seals to asphalt-surfaced pavements.
STATUS: Project is complete; published as NCHRP Report 680, available at