Healing: important factor for the design of asphalt pavements

Continuous traffic of heavy trucks on a road causes fatigue. The visco-elastic binder in asphalt pavements has in itself a mechanism that counteracts the development of damage due to fatigue: the self-repairing possibility, commonly named as healing. Healing repairs micro damage caused by fatigue during times where the pavement is not subjected to heavy loads. The designers of asphalt roads have taken into account this healing because they know that damage is repaired and will remain small. In the Netherlands, the designer manual of DWW estimates the healing factor at 4. This means that a road can be built about 4 cm less thick than without a healing factor (healing factor = 1). The decision about the healing factor was taken in the 1970s on the basis of research done on mixtures with new materials and rather soft binders (80/100). Since that time, recycling has become normal practice and other kind of binders have been introduced: multigrades, hard paving grades or PMB (polymer modified binder). To be sure that the healing factor these days is still the same as in the seventies, Benelux Bitume asked for a preliminary research. Samples were taken from a 350.000 ton production of asphalt containing 60% reclaimed asphalt and which has been used for a highway in the Netherlands. It was found that the healing factor in this material was reduced to about 1. For the covering abstract see ITRD E157233