Impact of Quarry Gradation on Base Course Aggregate Testing and Rutting Model Calibration Phase II

Rutting or accumulation of permanent deformation is the primary damage/distress mechanism of unbound granular base/subbase layers in pavements. Accordingly, rutting resistance is a major performance measure for designing pavements with granular base/subbase layers. Granular base/subbase permanent deformation may contribute significantly to the overall flexible pavement surface ruts. Low strength granular materials are generally more susceptible to higher permanent deformation accumulation. A properly compacted good quality aggregate base/subbase, on the other hand, adequately prevents settlement and any lateral movement in the layer through high shearing resistance and contributes significantly to dissipation of wheel load stresses. Indeed, the National Cooperative Highway Research Program (NCHRP) 4-23 study identified shear strength of unbound aggregates as one of the most significant mechanistic properties influencing pavement performance (Saeed et al., 2001). Moreover, shear strength property rather than “resilient modulus” (MR) has been always shown to better correlate with unbound aggregate permanent deformation behavior for predicting field rutting performance (Thompson, 1998; Tao et al., 2010; Xiao et al., 2012). The influence of stress state on MR of unbound materials is well known (e.g., Hicks and Monismith, 1971; Rada and Witczak, 1981; Thompson and Elliott, 1985; Uzan, 1985). Increased confining stress can substantially increase the resilient modulus of unbound pavement materials, particularly for coarse grained granular base materials, while increased shear stress can substantially decrease the resilient modulus, particularly for fine grained subgrade soils. The incorporation of stress state influences on the resilient modulus of unbound granular base and subbase layers was explicitly included in the American Association of State Highway and Transportation Officials (AASHTO’s) empirical pavement design procedure beginning in 1986. Although the influence of stress state on unbound resilient modulus is relatively well understood, its influence on the actual performance—rutting, cracking, roughness—of flexible pavements is less clearly known in practice. The design domains in which the influence of stress state is significant are also poorly defined. This issue has taken on more significance with the recent release of the AASHTO’s Pavement ME Design Guide implementation of the mechanistic-empirical (M-E) pavement design procedure. Whereas the earlier implementation of the M-E pavement design procedure in the public domain MEDPG software explicitly included stress dependence of unbound resilient moduli as Level 1 inputs, this capability has been removed from the new Pavement ME software implementation. This is arguably a step backwards for the pavement design profession. Road pavements in North Carolina (NC) have a long history of good performance of unbound base courses often constructed with granite type aggregate materials. The new AASHTO mechanistic-empirical (M-E) pavement design guide Pavement ME software does not credit the contribution of the unbound aggregate base sufficiently for it to be cost competitive. To properly account for aggregate quality impacting performance of pavements with unbound aggregate bases, the first challenge is to be able to incorporate aggregate shear strength or rutting potential into materials characterization through the inputs required by M-E design procedures such as Pavement ME.


  • English


  • Status: Active
  • Contract Numbers:

    RP 2015-23

  • Sponsor Organizations:

    North Carolina Department of Transportation

    Research and Development
    1549 Mail Service Center
    Raleigh, NC  United States  27699-1549
  • Project Managers:

    Kadibhai, Mustansir

  • Performing Organizations:

    University of Illinois, Urbana-Champaign

    Department of Civil Engineering, 201 Engineering Hall
    Urbana, IL  United States  61801
  • Principal Investigators:

    Tutumluer, Erol

  • Start Date: 20150315
  • Expected Completion Date: 20160116
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01582671
  • Record Type: Research project
  • Source Agency: North Carolina Department of Transportation
  • Contract Numbers: RP 2015-23
  • Files: RiP, STATEDOT
  • Created Date: Dec 2 2015 2:45PM