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DESIGN OF STABILISED BITUMEN MIXES FOR COLD RECYCLING OF PAVEMENTS IN ESTONIA

Most roads in Estonia have been paved with asphalt-grouted surfacing made of crushed limestone aggregate or gravel mixed with shale oil bitumen. The shale oil bitumen being used has good elongation features and very high adhesion with stone materials, but despite this, due to rapid ageing, the bitumen in old surfacing has become extremely hard and the surfacing needs softening. The method generally used is bitumen stabilisation. The cold and wearing resistance of the limestone used in Estonia is low, therefore the asphalt-grouted surfacing using these materials always undergoes surface dressing. The penetration of bitumen can be determined at any temperature if the softening point is known. There are two principally different positions in the design of stabilised mixes for cold recycling. In the first case the crushed asphalt is considered an independent grain material. Its grain composition is improved by adding new mineral aggregate with the necessary amount being calculated as a mixture of dense rock material. It is presumed that the added bitumen is only necessary for the adhesion of the grain and does not influence the viscosity of the bitumen existing in the crushed asphalt. This requires 2-3% of relatively viscous bitumen. Foamed bitumen or bitumen emulsion is used for the ease of mixing. Bitumen is usually harder in old surfacings and in such a case the old asphalt is seen as composite material consisting of mineral aggregate and bitumen. Stabilisation is needed to improve both the grain composition of the old material and to reduce the viscosity of the bitumen. The grain composition of the mineral aggregate is designed by including crushed stone according to the grain composition of the mineral aggregate in the crushed asphalt. Together with the calculation of the bitumen amount the viscosity of the bitumen to be added needs to be determined as well. If the bitumen in the old surfacing has aged too much, the bitumen added to it must be sufficiently liquid to soften it. The added bitumen reacts to the old bitumen very slowly enabling the mixture to be mixed. The negative aspect is that there will be liquid bitumen around the pieces of old asphalt for some time after the completion of the road until the surfacing achieves the necessary hardness. A threat of plastic deformation exists until then, if too much or too liquid bitumen has been added. The bitumen stabilised mixes in Estonia have norms for permanent void content and moisture sensitivity. The composition of the mixture (primarily the bitumen content and viscosity) are chosen according to experience and tested in the laboratory. The test results do not always meet expectations and have to be repeated after changing the composition of the mixture. For the covering abstract see ITRD E125033.

  • Corporate Authors:

    World Road Association (PIARC)

    La Grande Arche, Paroi Nord, Niveau 5
    F-92055 La Defense Cedex,   France 
  • Authors:
    • KOPPEL, M
  • Publication Date: 2002

Language

  • English

Media Info

Subject/Index Terms

Filing Info

  • Accession Number: 00988502
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD
  • Created Date: Apr 4 2005 12:00AM