Performance-Related Test of Recycled Aggregates for Use in Unbound Pavement Layers

摘要

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) frostfree layers, and (5) select fill material (sometimes as part of the working platform). The properties 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 (performance 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 performance 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 during construction, under repeated load and freeze-thaw cycling, and (8) drainability. Recycled aggregate properties that were determined to affect performance of unbound pavement layers are shear strength, frost susceptibility, durability, stiffness, and toughness. For this study, tests were conducted on RAP and RCP containing three different constituent aggregates (i.e., crushed limestone, granite, and gravel) to provide a range of materials 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.