Evaluation of aggregate subgrade materials used as pavement subgrade/granular subbase.

PDFTech ReportFHWA-ICT-15-013UILU-ENG-2015-2016R27-124Subgrade materialsSubgrade (Pavements)AggregatesGranular basesImage analysisGround penetrating radarRecycled materialsPavement performanceSpecificationsRuts (Pavements)Field studiesIllinoisIllinois Center for TransportationKazmee, HasanTutumluer, ErolIllinois Center for TransportationUnited States. Federal Highway AdministrationIllinois. Dept. of TransportationUS Transportation CollectionWith recent focus on sustainable construction practices and the ever-increasing transportation costs and scarcity ofnatural resources, integration of large-size and marginally acceptable aggregates and recycled materials (e.g.,reclaimed asphalt pavement [RAP]) with current construction specifications is becoming imperative. As an incentive,the Illinois Department of Transportation has been using large-size rocks, popularly known as aggregate subgrade.However, adequate scientific knowledge about material performance is largely unknown. To this end, a researchstudy was undertaken at the Illinois Center for Transportation to evaluate the adequacy and field performances ofIDOT\ue2\u20ac\u2122s new aggregate subgrade specifications. A state-of-the-art image analysis technique was used to characterizethe size and shape as well as the texture and angularity properties of selected aggregate subgrade materials. Forfield evaluation, 24 combinations of pavements were constructed over subgrade with controlled low immediatebearing value (IBV) or unsoaked California bearing ratio (CBR) strength properties. Construction quality control wasachieved through in-place density and modulus measurements on aggregate layers using a nuclear gauge,lightweight deflectometer, and soil stiffness gauges. Periodic rut measurements were carried out on the pavementsurface throughout the accelerated loading process using an Accelerated Transportation Loading Assembly(ATLAS). Contributions of the underlying pavement layers to the total rut accumulation were evaluated throughinnovative applications of ground-penetrating radar (GPR), a lightweight variable-energy penetrometer device, knownas the PANDA, and a geo-endoscopy probe. Layer intermixing and material migration at the aggregate subgrade\ue2\u20ac\u201csubgrade interface improved the foundation layer stiffness properties and pavement performance resultssignificantly. RAP-capped construction platforms consistently exhibited a higher magnitude of rutting. Performancesof flexible pavement sections were governed by the as-constructed HMA thicknesses, which varied considerablyduring the paver operation because of RAP subbase sinkage and the weak subgrade. Adequate validation andpotential revisions to current IDOT specifications were recommended