MODIFIED BITUMENS FOR ASPHALT WEARING COURSES

Asphalt mixes must have a high resistance to plastic flow to prevent deformation. New mixes have been investigated because mixes which had proved satisfactory for years failed during the hot summers of 1975 and 1976. The article deals with the use of binders of higher penetration index (pi) having reduced temperature susceptibility. A graph of the relative viscous strain with temperature shows that the stiffness increases over the temperature range with increasing values of pi. The author examines practical applications of higher pi bitumen with gap-graded mixes such as BS 594 rolled asphalt, and continuously graded mixes such as asphaltic concrete. Results from laboratory experiments are compared with those from field trials to show the relative deformation of gap-graded mixes as a function of pi. A pi of +2 reduces deformation to half that found when using normal bitumen; a pi value of +4 was found to reduce deformation by a factor of about four. Experience had shown no problems in mixing, laying and compacting asphalts with these values of pi. It was felt that there was a lack of knowledge of the behaviour of higher pi bitumen in continuously graded mixes, and it is recommended that the pi value should not be greater than +2 until more evidence from field trials is available. /TRRL/

  • Availability:
  • Corporate Authors:

    Shell International Petroleum Company Limited

    Shell Center
    London SE1 7NA,   England 
  • Authors:
    • Lucas, A G
  • Publication Date: 1977-5

Media Info

  • Features: Figures;
  • Pagination: p. 7-8
  • Serial:
    • Shell Bitumen Review
    • Issue Number: 55
    • Publisher: Shell International Petroleum Company Limited
    • ISSN: 0037-3516

Subject/Index Terms

Filing Info

  • Accession Number: 00164260
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Report/Paper Numbers: Analytic
  • Files: ITRD, TRIS
  • Created Date: Jan 30 1978 12:00AM