CrackingCracking takes many forms. To make the properrepairs, first you should determine the type of crack andthe cause.The most common types of cracks are.alligator, edge, edge joint, lane joint, reflection,shrinkage, and slippage.ALLIGATOR CRACKS.— Alligator cracks areinterconnected cracks, forming a series of small blocksresembling an alligator’s skin or chicken wire (fig.16-9). In most cases, alligator cracking is caused byexcessive movement of the surface over unstablesubgrades or base courses. The unstable support is theresult of saturated granular bases or subgrade.Normally, the affected area is not large. When it doesoccur on a large scale, the cracking is most likely due torepeated loads above the designed strength of thepavement.EDGE CRACKS.— Edge cracks are longitudinalcracks approximately 1 foot from the edge of theFigure 16-9.—Alligator cracks.Figure 16-10.-Edge cracks.pavement (fig. 16-10). Edge cracks can have transversecracks, branching in towards the shoulder. Normally,edge crack are caused by a lack of side or shouldersupport. They may also be caused by settlement oryielding of the base material underlying the crackedarea. This, in turn, may be the result of poor drainage,frost heave, or shrinkage from the drying out of thesurrounding earth.EDGE JOINT CRACKS.— Edge joint cracksoccur between the pavement and the shoulder (fig.16-11). They are normally caused by alternate wettingand drying beneath the shoulder surface. This can resultfrom poor drainage from a shoulder that is too high, orit can result from depressions along the pavement edge.The uneven pavement traps water on top, allowing it toseep into the base. Another cause could be heavy trucks,straddling the joint.LANE JOINT CRACKS.— Lane joint cracks arelongitudinal separations along the seam between twopaving lanes (fig. 16-12). This type of crack is usuallycaused by a weak seam or poor bond between adjoiningspreads in the pavement.Figure 16-11.-Edge joint cracks.Figure 16-12.-Lane joint cracks.16-17
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