A study of three South Carolina highway sections was conducted to determine the cause of poor performance. Comparison of test results from sites of excellent and poor performance revealed no important differences or defects in the asphaltic concrete pavement and the macadam or sand-clay base. Benkelman beam deflection measurements indicated that the US 378 section, located in the Middle Coastal Plain, had become more uniformly stable with the passing of time, and it was concluded that the early poor performance was probably due to high moisture content of the fills during construction. However, for the two highway sections (US 29 and US123) located in the Piedmont, very high deflections were noted at most sites of poor performance, and it was concluded that the high deflections and severe "alligator" cracking noted at these sites was due to the presence of elastic micaceous subgrade soil. Because the various forms of mica contain from 4% to 10% water of crystallization, whereas other common Piedmont soil minerals, except clay, contain little or no crystal water, the weight loss on ignition of the coarse fraction of a soil sample is a rough indication of the amount of mica responsible for the elastic nature of the soil. The elasticity as measured directly with the repeated-load consolidation test was compared with results of the ignition loss test for a number of samples, and the comparison yielded an inverse relationship which had a coefficient of correlation of 0.75. Integration of the Boussinesq equation for vertical stress and substitution of various values of modulus of elasticity as determined by ignition loss as well as direct measurement permitted the calculation of pavement deflection based on elastic theory. When the calculated deflections for the eighteen test sites were compared with the actual deflections as measured with the Benkelman beam, the coefficient of correlation was found to be 0.70 and 0.68 respectively. It was concluded that poor subgrade performance can be expected when cuts exceed 5 feet and that A-4 top soil and stiff, A-6 clay soil can carry heavy traffic without distress if a combined thickness of 12 inches of base and asphaltic concrete pavement is provided. The calculation of elastic deflection by the ignition loss method proved to be reasonably accurate in this investigation and is the basis for a recommended flexible pavement design procedure.

  • Corporate Authors:

    Clemson University

    Clemson, SC  United States  29634
  • Authors:
    • Rostron, J P
  • Publication Date: 1965-1-30

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: p. 20-140
  • Serial:
    • Issue Number: 100

Subject/Index Terms

Filing Info

  • Accession Number: 00084079
  • Record Type: Publication
  • Report/Paper Numbers: Bulletin
  • Files: TRIS
  • Created Date: Jun 10 1975 12:00AM