Slippage cracking results from which conditions?

• A. Weathering of the entire surface.
• B. Excessive surface deflection, weak base or subgrade, thin surface of base, poor damage, or overloading.
• C. Lack of good bond between layers, insufficient or absence of tack coat, high sand content mixture, or insufficient compaction.
• D. Route and seal, surface treatments, patch, thin overlay, remove and replace.

Answer: (C)

Slippage cracking happens when the bond between pavement layers is weak, so the surface can slide relative to the layer beneath under traffic and temperature changes. The correct choice highlights several interrelated factors that erode that bond: a lack of good interlayer adhesion, not using or using too little tack coat to promote bonding, a mix with high sand content that disrupts the asphalt film and adhesion, and insufficient compaction which leaves poor density and interlock. When bonding is poor or tack coat is missing, shear forces at the interfaces cause the surface to slip and crack along those joints. Inadequate compaction further reduces the strength of the bond by leaving voids and reducing cohesive integrity. By contrast, surface weathering, structural deflection from a weak base, or maintenance-only actions are not the direct root causes of slippage cracks.