Developing a Framework to Estimate RAP Binder Performance Grade and Assess Stockpile Variability Without Extraction

Abstract

The current method for qualifying Reclaimed Asphalt Pavement (RAP) involves the extraction and recovery of its binder using chemical solvents such as Trichloroethylene (TCE). However, TCE poses significant environmental and health risks and is currently subject to regulatory bans in the United States under updated Environmental Protection Agency (EPA) guidelines. This study introduces two experiments aimed at providing a comprehensive characterization of RAP without relying on extraction and recovery processes. The first experiment introduces a laboratory framework for estimating the performance grade (PG) of RAP binder without solvent extraction. The first step was to identify suitable performance tests for assessing RAP binder stiffness using laboratory-prepared artificial RAP. Among the evaluated tests, the Indirect Tensile Asphalt Cracking Test (IDEAL-CT) and High-Temperature Indirect Tensile Test (HT-IDT) showed strong logarithmic correlations with extracted RAP binder PG and were selected for the framework. The framework utilized these tests to evaluate field RAP samples and three re-mixed samples prepared by mixing the post-ignition aggregates with three asphalt binders of known PG at the same asphalt content as the field sample. Results showed that IDT Strength from HT-IDT and Pmax from IDEAL-CT provided reliable PG estimates for two of three field RAP sources. The second experiment examined RAP stockpile variability and its impact on mixture performance. First, both traditional and performance-based RAP characterization were conducted to evaluate the variability of 10 field RAP stockpiles. The results indicated that the stockpile analyzed was found to be uniform. Additional modified RAP samples were subsequently prepared in the laboratory to simulated stockpile segregation and contamination. Both traditional and performance-based RAP characterization methods detected variability due to segregation, but only the performance-based approach identified contamination without the need for binder extraction. Finally, the modified and control RAP samples were incorporated into a high RAP mix design for performance testing following a balanced mix design (BMD) approach. The control mixture demonstrated balanced performance, while modified mixtures showed inadequate cracking resistance.