Serious deformation has occurred in recent years on certain heavily-trafficked roads with rolled asphalt surfacing. The performance of this material is dependent on many compositional factors with the rheological properties of the binder being among the most important. The report considers those properties of binders that most affect the resistance to deformation of rolled asphalt. Thirteen binders were studied and mixtures containing them were subjected to design tests from BS 594: 1973 and the Wheel-tracking Test. These laboratory mechanical tests show that, within the range of binders tested, significant improvements in resistance to deformation can be achieved over a range of high road temperatures by increasing the softening point of the binder, irrespective of its penetration at 25 degrees C. A suggested specification for a 'heavy duty' bitumen is based on a softening point (R & B) to BS 4692 of 63 + or - 5 degrees C and a penetration at 25 degrees C to BS 4691, of 40 + or = 10. (A)

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