This laboratory study to evaluate the strength and load distributing characteristics of some designed dense bituminous mixes, investigated the design of single course surfacing materials (i.e. of 4-in. thickness), and the laboratory performance of such construction in comparison with the conventional two course surface. In recognition of the importance of treating the surfacing as an integral part of the flexible road construction, all tests were carried out on a simulated road support specially fabricated for the purpose; a test method for flexural strength and load distributing characteristics which related these characteristics to the stiffness of the supporting layer(s) beneath the asphalt surfacing was adopted. Asphalt specimens were tested upon a series of leaf springs suspended over two parallel bars; the stiffness of the support can be varied by adjustment of the spacing between the bars and by altering the spring stiffness. Details are given of the apparatus, the specimens and the test procedure and graphs are presented which illustrate the test results. Analysis of the results shows the effect of rate of testing upon ultimate load of the asphalt beams and upon their load spreading capacity. Optimum binder content for maximum value of these two properties are seen to be considerably different from each other and in the former case to be rate-sensitive. It is noted that the single course designed mixes are generally superior over the standard, mixes in conventional 2-course construction. Based on this study, certain conclusions are drawn relating to: reduced voids and increased binder content at the critical lower face of slab; reduced binder content at the upper face; the removal of a relatively weak interface at an approximately mid-height level in the surfacing; the use of larger maximum size aggregate; and simplification of the laying procedure.

  • Supplemental Notes:
    • Proceedings of the meeting held in Houston, Texas, February 1973.
  • Corporate Authors:

    University of Minnesota, Minneapolis

    155 Experimental Engineering Building
    Minneapolis, MN  United States  55455
  • Authors:
    • Lees, G
    • MacKellar, K S
  • Conference:
  • Publication Date: 1973

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: p. 1-36
  • Serial:
    • Volume: 42

Subject/Index Terms

Filing Info

  • Accession Number: 00127323
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Dec 16 1975 12:00AM