In many cases it is economical and convenient to improve the structural condition of a pavement by means of an asphalt overlay. A number of different methods can be used for the design of the overlay, one of the most popular being based on deflection measurements and limiting deflection criteria. New methods based on a structural design approach have been proposed by various investigations. One of the difficulties of this approach is the measurement of the moduli of the various pavement layers to use in the theoretical calculations. This paper presents two new charts for designing overlays developed from the results of a theoretical analysis of model pavements using linear elastic theory. The one chart is used to determine the thickness of overlay required to reduce the deflection to the design limit. Since this chart was developed using a dual-load configuration which closely simulates that used in the Benkelman beam deflection test procedure, it is believed that it will give more accurate results than existing charts developed from consideration of a single loaded area. It is proposed that design deflection limits for overlays constructed on asphalt surface roads with granular bases be obtained from the deflection-load repetition relationship developed by the asphalt Institute, and the assumption is made that this will limit distortion to an acceptable degree during the design period. The other chart is designed to eliminate cracking of the overlay and gives the relationship between radius of curvature and tensile strain in the asphalt layer for various thicknesses of asphalt. It is concluded that the use of these charts could be useful for designing overlays in cases where it is necessary to use simple evaluation techniques and simple overlay design procedures. However, it is shown that the stres-dependency of materials in the existing pavement can have a significant effect on the relationships established, and this can only be taken into account if more sophisticated testing and analysis procedures are used. Two simple methods are described for measuring the in-situ moduli of pavement layers. The first involves measurement of both deflection and radius of curvature, and on roads with thin surfacings enables estimations to be made of the base/subgrade modular ratio and of the base modulus. It is concluded that this information would be of particular value when having to make a decision on whether it would be worthwhile improving a road by means of an asphalt overlay. The second method uses measurements of the deflection at various depths within the pavement structure using a modified Benkelman beam procedure. This not only enables the vertical strains at any point to be calculated (from the change in deflection within a finite depth), but also enables the moduli of the various materials to be calculated using elastic theory. In this way any weak layers within the structure can be identified or the effect of an overlay or new loading condition on the vertical strains within the structure can be determined. An example of the use of the method is given in the design of an overlay to strengthen an airfield runway for the coming of boeing 747 aircraft. /AUTHOR/

  • Supplemental Notes:
    • Presented at the Third International Conference on the Structural Design of Asphalt Pavements, Grosvenor House, Park Lane, London, England, Sept. 11-15, 1972.
  • Corporate Authors:

    International Conf Struct Design Asph Pvmts (3rd)

    University of Michigan, Department of Civil Engineering
    Ann Arbor, MI  United States  48104

    International Conf Struct Design Asph Pvmts (3rd)

    University of Michigan, Department of Divil Engineering
    Ann Arbor, MI  United States  48104

    Interrational Conf Struct Design Asph Pvmts (3rd)

    University of Michigan, Department of Civil Engineering
    Ann Arbor, MI  United States  48104
  • Authors:
    • Grant, M C
    • Walker, R N
  • Conference:
  • Publication Date: 1972-9

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 1155-66
  • Serial:
    • Volume: 1

Subject/Index Terms

Filing Info

  • Accession Number: 00261891
  • Record Type: Publication
  • Report/Paper Numbers: Proceeding
  • Files: TRIS
  • Created Date: Oct 22 1974 12:00AM