Voids Beneath Pavements...

Concrete pavements experience daily and seasonal variations in joints opening and closing.  During the open periods, water may enter the base.  The weakened base material may "pump" up through the joints with loading and therefore cause a void under the joint.  Other sources of water such as springs and water main leaks may also erode the material under the slab.  It is important to find and repair these voids before catastrophic failure leading to expensive repairs to the concrete slab.  Deflection testing is sometimes used to locate the voids and determine load transfer efficiency.  This method is not discussed here.  Methods that have been found successful in locating voids under concrete are listed below.

Techniques Recommended

Surface NDT Methods:

• Ground penetrating radar (GPR)
• Impact Echo - other acoustic methods

While other methods are available or under development, the ones listed above provide cost-effective determination of pavement thickness.

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