A comparison of the ROADHOG and AASHTO (1993) overlay design procedures for conventional flexible pavements is presented. Both procedures use a structural deficiency approach to overlay design yet differ in the methods used to estimate the effective structural number of an existing pavement and to estimate the in situ subgrade resilient modulus. Both methods use pavement surface deflections to backcalculate or estimate required design parameters. Specific comparisons include backcalculated subgrade resilient modulus, effective structural number, and recommended overlay thickness for a number of conventional flexible pavement configurations. Pavement surface deflections are generated using the ILLI-PAVE finite-element pavement model and the ELSYM5 elastic layer model. Pavement parameters varied to establish the deflection data base, including asphalt concrete surface thickness and resilient modulus, base course thickness and resilient modulus, and subgrade resilient modulus. The comparisons show that the AASHTO overlay design procedure recommends thicker overlays than does the ROADHOG procedure for pavements overlying relatively stiff subgrade soils. The difference in recommended overlay thickness is linked to differences in the estimates of both SN sub f, the structural number required to carry future traffic, and SN sub eff, the effective structural number of the existing pavement. The two design procedures recommend similar overlay thicknesses for pavements overlying soils with relatively low resilient modulus values. The analyses also show that the backcalculated value of subgrade resilient modulus plays a larger role in determining the overlay thickness for the AASHTO procedure than for the ROADHOG procedure.


  • English

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 94-101
  • Monograph Title: Pavement design and analysis
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00713508
  • Record Type: Publication
  • Files: TRIS, TRB, ATRI
  • Created Date: Nov 7 1995 12:00AM