Validation of Hot-Poured Crack Sealant Performance-Based Guidelines

About the report:

This report summarizes a comprehensive research effort to validate thresholds for performance-based guidelines and grading system for hot-poured asphalt crack sealants. A series of performance tests were established in earlier research and include the crack sealant bending beam rheometer (CSBBR), crack sealant direct tension test (CSDTT), the crack sealant adhesion test (CSAT), a rotational viscosity test, and a dynamic shear test. Validation was accomplished through an extensive field performance study incorporating a wide spectrum of commonly used sealants installed in eight test sites around the United States using two basic treatment methods: (1) clean and seal, and (2) rout and seal. Performance of these sealants and treatment methods were monitored for 3 years to quantify relative performance, primarily through adhesive and cohesive failures, as well as overband wear. Field samples were also collected from the sites to conduct laboratory testing to reflect in-service properties. A statistical method was used to develop correlations of the test's parameters with the field performance. The composite score approach, combining ranking and correlation, was used to develop a quantitative scale for determining the level of acceptance. Based on the composite score, a strong or acceptable correlation was obtained between field performance and laboratory test parameters. After the correlation between field performance and lab results was confirmed, the thresholds for test methods were selected or fine-tuned.

An investigation was also conducted to evaluate the short-term and long-term aging effects of hot-poured crack sealants through a differential aging test. Rheological and mechanical properties of sealants at different aging stages were monitored to characterize the aging effects. Laboratory aging of sealants was studied using three different aging methods: kettle aging, melter aging, and vacuum oven aging (VOA). The aging index was used to evaluate the effect of these aging methods. By a comparison of the stiffness master curves obtained from the CSBBR test for field-aged samples and laboratory-aged samples, VOA was validated as a reasonable aging method for simulating 2 to5 years of field aging.

The research proposes new guidelines for full implementation as AASHTO specifications. In addition to validated and revised thresholds for existing protocols, the research proposed a modified adhesion test and a simplified test for tracking resistance. Close inspection of the installation techniques and early performance feedback also supported the development of guidelines for crack sealant installation and application.

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