THE PERMANENT DEFORMATION CHARACTERISTICS OF A DENSE BITUMEN MACADAM SUBJECTED TO REPEATED LOADING

Experiments were performed on continously graded asphaltic material to check the validity of a procedure which involves the calculation of the vertical and horizontal stress distribution through the pavement using linear or non-linear elastic theory and the evaluation of the corresponding permanent strain distribution from the results of appropriate laboratory tests; summation of the permanent strain with depth gives the permanent deformation of the surface. Dense bitumen macadam made with nominally 100-per bitumen and crushed rock aggregate (porphyry) of 25-mm maximum particle size were used. Repeated load, triaxial tests were used. Tests were conducted under controlled stress conditions, and resilient as well as permanent strains were measured. A series of creep tests were also performed. The six major variables investigated were vertical stress, temperature, confining stress, frequency of the vertical stress pulse, rest periods and binder content. The studies showed that an increase in temperature caused a substantial increase in strain. An increase in vertical stress caused an increase in strain and an increase in confining stress caused a decrease in strain. The level of static confining stress which gave the same strain as the dynamic confining stress was approximately equal to the mean level of that stress. The realistic changes in the relative lengths of vertical and confining stress pulses did not affect the strain. The rate of strain appeared to be time dependent at frequencies above 1 Hz. Rest periods between vertical stress pulses had negligible effect on strain. An optimum binder content of 4 percent existed for maximum resistance to strain between 10 and 30 c. At 40 C, better resistance was achieved with a 3 percent binder content. There was some evidence of a simple relationship between dynamic test results and those from simple creep tests. Interpretation of the results in terms of mix stiffness as a function of bitumen stiffness was encouraging. The results obtained from laboratory tests when applied to the pavement design problem produced reasonable values of rut depth.

  • Corporate Authors:

    University of Minnesota, Minneapolis

    155 Experimental Engineering Building
    Minneapolis, MN  United States  55455
  • Authors:
    • BROWN, S F
    • Snaith, M S
  • Conference:
  • Publication Date: 1974

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: p. 224-252
  • Serial:
    • Volume: 43

Subject/Index Terms

Filing Info

  • Accession Number: 00125404
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Oct 18 1975 12:00AM