Poor Distributor Performance
The improper set up of the distributor can lead to bond coat applications that are streaky or striped in appearance. This is refered to as “corn rows” or "Zebra Tack". This does not produce good bond strengths. Some research reports that a mere 10% loss in bond strength resulted in a 50% loss in fatigue life. If this is observed in the field, it should be stopped until the spray pattern can be corrected to produce an uniform application.
Poor Hand spray Technique
The random pattern on hand sprayed bond coat will not produce good bond strength. Some research reports that a mere 10% loss in bond strength resulted in a 50% loss in fatigue life. If this is observed in the field, it should be stopped until the applicator can spray in a pattern that provides uniform application.
Loss of Bond Causes Shoving
When there is a weak bond or no bond between pavement layers the top layer moves independently from the base and begins to deform.
Poor bond strength causes delamination
Poor bond strength between layers results in large sections of the top layer breaking loose. From the photo, there is an apparent clean break at pavement boundary and little evidence of any bond coat on the base layer.