The unsupported sections of the slab could not support the imposed
aircraft loads and resulted in the cracking.
In order to prevent a reoccurrence of this type of distress the following
guidance was issued:
The minimum thickness of separated unbonded overlays should be eight
Joint spacing in unbonded, plain concrete overlays will be 12.5 feet
by 15 feet.
When designing separated, unbonded overlays, rigid type separation
courses such as lean concrete or cement treated aggregate should not
When the thickness of the bond breaking course, due to leveling
requirements, exceeds approximately four inches, the design equation
for an unbonded overlay is not valid and the new pavement must be
designed as a new slab on grade using a subgrade modulus (k value)
not exceeding 500 pci.