A laboratory evaluation is reported of the properties of asphalt surfacing materials as they affect the tendencey for tendency for cracking to occur at low temperatures. The laboratory simulation and procedures are detailed in the measurement of thermally induced fracture stresses and temperature. The basic concept involved cooling a beam of compacted asphalt at constant rate, while mainaining it at as nearly constant length as possible, and measureing the stress generated by means of strain gauges. The asphalt mix variables investigated were as follows: rheological characteristics of bitumens (including consistency or hardness); asphalt mix type (whether continuously or gap graded, etc.); aggregate properties; bitumen content at variable filler-biumen ratio; bitumen content at constant filler-bitumen ratio; and polymer additives. It is concluded on the basis of the work that the thermal failure temperature for a given asphalt is heavily influenced by the properties of the bitumen used and can be related to the low-temperature stiffness of the bitumen calucalted from its fundamental rheological properties. Low Newtonian viscosity, low temperature susceptibility of bitumen are all factors conducive to reducing asphalt failure temperature. Variations in aggregate grading and properties have little or no effect on the resistance of asphalt to thermally-induced fracture. It was also found thet increasing the binder content of asphalt within paracticable limits only slightly reduces its thermal fracture susceptibility. Since the failure temperature of asphalt is independent of the rate of cooling, it is deduced that failure occurs when the bitumen attains a critical physical state, rather than when incremental stresses accumulate to exceed the fracture strength of the asphalt. The addition of synthetic polymers to bitumen can reduce asphalt fracture susceptibility, but their use for this purpose is likely to be small until better cost-effective species are identified.

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: p. 285-331
  • Serial:
    • Volume: 43

Subject/Index Terms

Filing Info

  • Accession Number: 00125406
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Oct 18 2000 12:00AM