DEFLECTION CRITERIA FOR FLEXIBLE PAVEMENTS AND THE DESIGN OF OVERLAYS

The long-term performance of flexible pavements can be determined by the magnitude of the transient deflections which occur under traffic. A continuous programme of deflection measurements extending over fifteen years has been carried out on the full-scale road experiments in flexible construction built by the Road Research Laboratory. Over 300 experimental sections and in addition 30 lengths of major road whose construction is of particular interest have been tested annually with the Benkelman Deflection Beam under a wheel-load of 3175 kg (7000 lb). The measured deflections have been corrected for the influence of temperature on the stiffness of the bituminous components, and 'standard' deflections at 20 degrees C have been related (a) to the age of the road expressed in terms of the cumulative total of equivalent standard 8200 kg (18,000 lb) axle loads carried, and (b) to the condition of the pavement in terms of rutting and cracking. The deflection histories thus derived enable the development of critical conditions within the pavement when strengthening of the road would be most appropriate, to be related to deflection behaviour under traffic. Well-defined relations between standard deflection values measured early in the life of pavements and their lives have been established. For lives exceeding 1 million standard axles they are of the form life (deflection) cubed. For pavements with crushed stone, rolled asphalt and coated macadam bases under rolled asphalt surfacings the surves are similar, but acceptable deflection levels are lower on pavements with cemented bases. Charts making due allowance for the slow increase in deflection which takes place during the life of a pavement are being prepared to enable prediction of road performance from deflection values measured at any time to be made. An example is given. Overlays have been applied to certain full-scale road experiments as they have been retired from service and deflection studies have been continued. The behaviour of overlays laid to strengthen normal roads is being similarly studied. Relations have been derived for the reduction in deflection brought about by over-lays of different thicknesses applied to various types of pavement on different subgrades. The results have been compared with those predicted from the application of multi-layer elastic theory. Deflection histories of overlaid pavements have been used to prepare recommendations for overlay thicknesses to achieve any required extension of pavement life. The implementation of recommendations for pavement strengthening is considered. /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  USA  48104

    International Conf Struct Design Asph Pvmts (3rd)

    University of Michigan, Department of Divil Engineering
    Ann Arbor, MI  USA  48104

    Interrational Conf Struct Design Asph Pvmts (3rd)

    University of Michigan, Department of Civil Engineering
    Ann Arbor, MI  USA  48104
  • Authors:
    • Lister, N W
  • Conference:
  • Publication Date: 1972-9

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 1206-26
  • Serial:
    • Volume: 1

Subject/Index Terms

Filing Info

  • Accession Number: 00261887
  • Record Type: Publication
  • Report/Paper Numbers: Proceeding
  • Files: TRIS
  • Created Date: Oct 22 1974 12:00AM