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S U M M A R Y Unbound pavement layers in flexible and rigid pavements generally serve to provide (1) a working platform, (2) structural layers for the pavement system, (3) drainage layers, (4) frost- free layers, and (5) select fill material (sometimes as part of the working platform). The prop- erties of recycled aggregates (recycled asphalt pavement [RAP] and recycled concrete pavement [RCP]) greatly influence their performance as unbound granular pavement layers. Failure of an unbound pavement layer results in pavement distresses. Fatigue cracking, rutting/corrugations, depressions, and frost heave of flexible pavements are distresses (per- formance parameters) that can result from poor performance of aggregate in unbound base and subbase layers. Similarly, cracking, pumping/faulting/loss of support, frost heave, and erosion in rigid pavements can result from poor performance of subbase layers. Factors contributing to distresses in both rigid and flexible pavements due to the poor per- formance of unbound layers include (1) shear strength, (2) density, (3) gradation, (4) fines content, (5) moisture level, (6) particle angularity and surface texture, (7) degradation dur- ing construction, under repeated load and freeze-thaw cycling, and (8) drainability. Recycled aggregate properties that were determined to affect performance of unbound pavement lay- ers are shear strength, frost susceptibility, durability, stiffness, and toughness. For this study, tests were conducted on RAP and RCP containing three different con- stituent aggregates (i.e., crushed limestone, granite, and gravel) to provide a range of ma- terials with poor to excellent performance. The recycled materials were blended with a virgin aggregate known to provide good performance in unbound pavement layers. Laboratory test data were analyzed. The following tests were found to produce statistically significant performance indicators of recycled aggregates in unbound pavement layers: ⢠Screening tests for sieve analysis and the moisture-density relationship, ⢠Micro-Deval for toughness, ⢠Resilient modulus for stiffness, ⢠Static triaxial and repeated load at optimum moisture content and saturated condition for shear strength, and ⢠Frost susceptibility (tube suction). Requirements for test parameters for recycled materials were established to evaluate recy- cled materialsâ suitability for use in particular traffic and climatic conditions. The research team developed a decision chart incorporating aggregate shear strength, stiffness, toughness, and frost susceptibility to provide a measure of the performance potential of a particular aggregate. The researchers also developed a validation plan to evaluate the research results in the long term. This plan proposes accelerated pavement testing of specially constructed pavement sections and long-term performance monitoring of in-service test pavements. Performance-Related Tests of Recycled Aggregates for Use in Unbound Pavement Layers 1
