Question

Please give a good explanation and a comprehensive answer.

Where in the asphalt layer, would you expect to find a tension crack forming(initiating) and why?

Answer 1

Tension cracks in asphalt layer in pavement can form at both top and bottom of the pavement.

In thin pavements cracks initiate from the bottom due to heavy tensile stress at the bottom and then propagates or appears to the top as one or more longitudinal cracks which is known as bottom up or classical or fatigue cracking.

In thick pavements cracks are developed at top layer of pavement in areas of high tensile stress due to the interaction of wheel tyre and pavement and when loads are repeated these longitudinal cracks combine together then it takes the form of crocodile or alligator cracks.

These cracks prevent the filtration of water and turns into pot hole if repeated to heavy loads further.

Causes of these fatigue or alligator or crocodile cracks are as follows:-

* Poor construction i.e poor compaction of subgrade

* Inadequate structural design

* Excessive loads increment than anticipated during design

* Brittleness of binder materia

* Overloading

* Excessive deflection of surface over unstable subgrade, subbase or base

* When tensile strain at bottom layer is beyond certain limit.

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