Joint spalling is the breakdown of the slab edges within 0.5 m (1.5 ft) of the joint. A joint spall usually does not extend vertically through the slab, but intersects the joint at an angle. Spalling results from:
Excessive stresses at the joint caused by traffic loading or by infiltration of incompressible materials.
Weak concrete at the joint caused by overworking.
Water accumulation in the joint and freeze-thaw action.