Revision and Further Validation of Surface Performance-Graded Specification for Chip Seal Binders
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The design and selection of chip seal binders for adequate performance in service are currently based on specifications that include tests of emulsion residues or hot-applied asphalt cements at standard temperatures that do not cover the entire range of in-service temperatures, measure properties that are not performance related, and do not consider representative aging conditions for the critical first year. A surface performance-graded (SPG) specification for the evaluation and selection of chip seal binders that addressed these shortcomings was developed as part of previous Texas Department of Transportation (DOT) and NCHRP research projects. In the current study sponsored by the Texas DOT, the SPG specification was revised and further validated. This was accomplished through use of a single emulsion residue recovery method, determination of performance-related properties and exploration of additional criteria, and further validation of the SPG specification thresholds for these properties based on field performance monitoring and a comparison with laboratory results. This study was limited to producing a revised SPG specification for performance-related properties that addressed aggregate retention and bleeding in service. Specifically, the threshold for minimum shear strain at 0.8 G*i was reduced from 25% to 17.5%, and the m-value was removed. The effects of construction and quality control processes were beyond the scope of this study, and additional specifications are needed for use in conjunction with the SPG specification to address these issues and ensure adequate performance.
