CHANGES OF THE QUALITY OF AGGREGATES THROUGH HEATING IN DRYING DRUM DURING PRODUCTION OF ASPHALTIC CONCRETE

FOERAENDRING AV STENMATERIALEGENSKAPER GENOM UPPHETTNING I TORKTRUMMA VID FRAMSTAELLNING AV ASFALTMASSA

In connection with disputes on the quality of laid asphaltic concrete, laboratory analyses are made on aggregates recovered from bituminous mixes. The aggregates have in such cases been exposed to high temperatures in the drying drum and their properties may have changed. A literature study of the influence of high temperatures has been made and also some former experiences are described. According to laboratory tests, temperatures of 400-500 deg C are needed before measurable changes in the mechanical properties of aggregates can be obtained. Some rock materials can be especially susceptible to thermal action; examples are some varieties of marble and mica-rich gneiss. Rock materials, rich in quarz, are weakened at a temperature of 573 deg C (because of a crystallographical change in quarz). At a temperature of 700 deg C most aggregates are more or less weakened. Dark, mafic rocks can be altered and oxidized without degrading to a greater extent. The influence of high temperatures increases with the heating time. Several full-scale experiments have been made abroad during which the aggregate has been investigated before and after passing the drying drum. As a rule, the mechanical properties have changed very little. Apparently, the time the aggregate is exposed to high temperature is too short for a thermal degradation. Weak particles can even be broken down to fines and the aggregate recovered from the mix can have improved mechanical properties. The adhesion to binder is shown to improve after heating. Tests for investigation of the thermal properties of aggregates are used abroad. However, a special test method has not been justified in Sweden. Further investigations should be made with special aggregates, e.g. mica-rich gneiss. (Author/TRRL)

• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/issn/03476049
• Corporate Authors:

  Swedish National Road and Transport Research Institute (VTI)

  Linköping,   Sweden  SE-581 95
• Authors:
  • HOEBEDA, P
• Publication Date: 1985

Language

• Swedish

Media Info

• Features: Appendices; Figures; Photos; References;
• Pagination: 16 p.
• Serial:
  • VTI meddelande
  • Issue Number: 457
  • Publisher: Swedish National Road and Transport Research Institute (VTI)
  • ISSN: 0347-6049

Subject/Index Terms

• TRT Terms: Adhesion; Aggregates; Asphalt concrete; Bituminous binders; Dryer drum process; Heating (Structures); High temperature; Laboratory tests; Mechanical properties; Quality control; Thermal properties
• Uncontrolled Terms: Quality
• Subject Areas: Geotechnology; Highways; Materials;

Filing Info

• Accession Number: 00466187
• Record Type: Publication
• Source Agency: Swedish National Road and Transport Research Institute (VTI)
• Files: ITRD, TRIS
• Created Date: Mar 31 1988 12:00AM