OVERLAY DESIGN: WHAT ARE THE STATES PRESENTLY DOING?

A SURVEY WAS CONDUCTED BY AN NCHRP PROJECT TO OBTAIN INFORMATION FROM THE STATES ON THEIR METHODS OF USING THE AASHO INTERIM GUIDES FOR THE DESIGN OF PAVEMENT STRUCTURES AND ON RELEVANT DESIGN PROCEDURES. THE QUESTIONNAIRE TO EACH STATE CONTAINED 70 QUESTIONS, FOUR OF WHICH PERTAINED DIRECTLY TO ASCERTAINING CRITERIA USED IN UPGRADING THE EXISTING PAVEMENT STRUCTURES ON HIGHWAYS. A SUMMARY IS PRESENTED OF THE REPLIES TO THE QUESTIONNAIRES. BASICALLY, THE STATES USED THE FOLLOWING FIVE CATEGORIES FOR PROCEDURES FOR ESTIMATING THE OVERLAY THICKNESS REQUIRED: EXPERIENCE, FLEXIBLE GUIDES, DEFLECTION, AASHO PSI, AND VISUAL. THE FOLLOWING SEVEN EXPERIENCE FACTORS WERE PART OF THE CRITERIA FOR ESTABLISHING OVERLAY THICKNESS: CONDITION SURVEY, RIDING QUALITY, MAINTENANCE COST, MATERIALS SURVEY, TRAFFIC, SKID, AND DEFLECTION. THE MAJOR CATEGORIES OF OVERLAY DESIGN PROCEDURES ARE DISCUSSED AND DESCRIBED. AN ANALYSIS OF REPLIES REGARDING THE MINIMUM OVERLAY THICKNESSES INDICATES THAT THE MINIMUMS WERE NOT ABSOLUTE VALUES, BUT RATHER GENERAL MINIMUMS THAT MAY BE VARIED DEPENDING ON PROJECT CONDITIONS. RIGID PAVEMENTS REQUIRE A GREATER MINIMUM OVERLAY THICKNESS, PROBABLY TO COMBAT REFLECTION CRACKING OVER THE JOINTS. THE REVIEW OF CURRENT OVERLAY DESIGN PRACTICES INDICATES THAT ONLY A FEW DESIGN METHODS ARE AVAILABLE, AND THESE ACCOUNT ONLY FOR WHEEL LOAD STRESSES, WITH NO CONSIDERATION OF VOLUME CHANGE STRESSES. ONLY THOSE METHODS UTILIZING DEFLECTIONS EVALUATE THE LOAD-CARRYING CAPACITY OF THE IN-PLACE PAVEMENT STRUCTURE. THE AASHO FLEXIBLE GUIDES HAVE BEEN UTILIZED IN THE DESIGN OF OVERLAYS, BUT THIS IS AN EXTENSION OF AN EMPIRICAL EQUATION BEYOND ITS LIMITS OF DERIVATION. THIS IS TRUE IN REGARD TO USE WITH RIGID PAVEMENTS BECAUSE THE BASIS FOR ASSIGNMENT OF THE LAYER EQUIVALENCE VALUE TO CONCRETE IS UNKNOWN. IT IS FELT THAT, ALTHOUGH EXPERIENCE IN EMPIRICAL APPROACHES WORKS FAIRLY WELL, THERE IS AN IMMEDIATE NEED FOR A RATIONAL OVERLAY DESIGN PROCEDURE THAT ENCOMPASSES BOTH WHEEL LOAD AND VOLUME CHANGE STRESSES.

  • Digital Copy:
  • Supplemental Notes:
    • Paper sponsored by Committee on Salvaging Old Pavements by Resurfacing, Maintenance of Bituminous Pavements, and Maintenance of Portland Cement Concrete Pavements and presented at the 48th Annual Meeting.
  • Authors:
    • McCullough, B Franklin
  • Publication Date: 1969

Media Info

  • Media Type: Print
  • Features: Figures;
  • Pagination: pp 4-9
  • Monograph Title: Design of overlays and pavement rehabilitation
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00218571
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Feb 16 1970 12:00AM