Statewide Implementation of the Surface Performance Graded Specification for Chip Seal Binders in Texas
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Date
2017-08-01
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Abstract
Over the past 15 years, a Surface Performance-Graded (SPG) specification for chip seal binders was developed and validated using laboratory measurements and visual field performance of 120 highway sections (HSs). The SPG specification was established in an effort to extend the service life of chip seals by providing a binder grading system and associated selection method that: (1) accounts for differences in climate and (2) utilizes existing equipment and performance-based properties that preclude bleeding and aggregate loss in the critical first year of service after construction. The third year of implementation of the specification is ongoing and the current work is a record of the efforts during this period which involved simultaneous work on validating the existing performance parameters, educating the end users about the specification and its development, and addressing their concerns.
The improvement in the field performance correlation of the SPG parameters by considering construction factors signified the importance of the combined utilization of construction guidelines and material-related specifications. In terms of industry interaction, two round robins were conducted with TxDOT and various binder suppliers in Texas as a result of which: (a) the SPG specification was modified to incorporate offset 6° increments during the grading process and thus considerably reducing the number of grades in Texas and, (b) the need for a parameter that is indicative of modification was identified. On reviewing the existing phase angle threshold for its sensitivity to modification type and aging, alternative parameters were explored. Although the MSCR test parameters were not indicative of field performance, they seemed promising in terms of indicating binder modification. Based on the extensive literature review, guidelines were provided to modify the test protocol for use with chip seal binders. Further work on modifying the MSCR test protocol for chip seal applications and improving the test conditions for low temperature binder characterization were recommended.
The improvement in the field performance correlation of the SPG parameters by considering construction factors signified the importance of the combined utilization of construction guidelines and material-related specifications. In terms of industry interaction, two round robins were conducted with TxDOT and various binder suppliers in Texas as a result of which: (a) the SPG specification was modified to incorporate offset 6° increments during the grading process and thus considerably reducing the number of grades in Texas and, (b) the need for a parameter that is indicative of modification was identified. On reviewing the existing phase angle threshold for its sensitivity to modification type and aging, alternative parameters were explored. Although the MSCR test parameters were not indicative of field performance, they seemed promising in terms of indicating binder modification. Based on the extensive literature review, guidelines were provided to modify the test protocol for use with chip seal binders. Further work on modifying the MSCR test protocol for chip seal applications and improving the test conditions for low temperature binder characterization were recommended.
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SPG, chip seals, MSCR, specification, polymer modified binders