Fatigue Cracking of Hot Mix Asphalt

Fatigue cracking is a type of crack pattern that occurs when the asphalt of a pavement has been stressed by repetitive axle load applications beyond the stress limits of its fatigue life.

An axle load application is the pressure  exerted by the weight of all wheels connected to a specific axle of a vehicle.

The fatigue life is defined as the number of repetitive axle load applications that the asphalt can take before its structure fails and strain occurs.

Thus the Primary Cause of Fatigue Cracking Are:


  • Drainage problems resulting in water building up, redribbonlive saturation and reduction of the asphalt strength & fatigue life.
  • Repetitive axle load of vehicles passing over the asphalt that are beyond regulations; typically large trucks carrying excess weight.
  • Poor quality management of the construction company that laid the asphalt


Potholes are one of the potential results of fatigue cracking. If the road was built using thin layers of hot mix asphalt and fatigue cracking moves to severe & extensive levels, ristomanager then it is possible for sections of the asphalt to separate from the road.

Propagation of Fatigue Cracking


  • For thin layers of hot mix asphalt, fatigue cracking begins at the bottom of the layer.
  • For thick layers of hot mix asphalt


Moisture Driven Asphalt Degradation
Above it was mentioned that the build up of water & resulting water saturation of the road asphalt matrix can have severe and deleterious effects on the structural strength MATRIX CRACK of the material. This system operates in three different mechanisms that each degrade the integrity of the built hot mix asphalt road.


  • Strength and stiffness reduction through a number of more complex mechanisms.
  • Stripping: the breakage of bonds between the aggregate and the asphalt.
  • Due to the nature of hydrogen bonding in water, ice has a lower density and thus a larger size (at constant mass) than liquid water. Any moisture that is within the mixture will thus expand when frozen. This in itself can cause fracturing and on a larger scale; cracking. On the macro-scale: the process works to create a feedback cycle once fatigue cracking has set in.


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