UFC 3-260-02
30 June 2001
and the combined thicknesses of existing rigid pavement and any base or subbase layers above the
subgrade.
e. Reflective Cracking. If a flexible overlay is placed over a rigid pavement, the underlying
joints will reflect through the overlay, and these cracks will progressively deteriorate by raveling.
This reflective cracking is primarily caused by seasonal and diurnal environmental changes
occurring in the overlaid rigid pavement, and reflective cracking will often appear during the first
winter after the placement of the overlay. At present there is no completely reliable method of
preventing reflective cracking. Consequently, in many cases, the designer should probably consider
a flexible overlay as a maintenance tool to upgrade the serviceability and to a more limited extent,
the structural capacity of a rigid pavement for a relatively limited time while more comprehensive
rehabilitation is postponed to the future. Some methods of ameliorating the adverse effects of
reflective cracking include:
(1) Overlay Thickness: The thicker the overlay, the longer the cracking will be postponed
and the slower it will deteriorate. Hence, abiding by minimum flexible overlay thicknesses is an
important issue.
(2) Saw and Seal: Since there is no way to reliably avoid reflective cracking, another
approach is to saw the flexible overlay directly above the rigid pavement joints and seal this with
an appropriate sealer. These sealed cuts are then more easily and effectively maintained than the
reflective cracks would be. The Air Force has found this to be an effective approach, and it is
generally their preferred approach to dealing with flexible overlays over rigid pavements.
(3) Geotextiles: Geotextiles have shown a limited ability to slow the development and
severity of reflective cracking in warm climates. Field trials found that in Area I of Figure 17-3,
geotextiles were usually helpful, in Area II they gave mixed results, and in Area III, they were
ineffective in dealing with reflective cracking. The minumum overlay thickness is 100 millimeters
(4 inches).
(4) Crack & Seat and Rubblizing: An alternative approach is to break the existing rigid
pavement slabs into smaller individual segments (crack and seat) or to pulverize them into
shattered small fragments (essentially rubblize to aggregate) before overlaying . Concetually, the
shattered slabs or rubblized concrete fragments are then too small to develop movements to
generate reflective cracks. This technique has proven successful on highways, but experience on
thicker pavements such as found on airfields is very limited at present.
(5) Bond Breakers: Open graded materials, aggregate bases as part of the flexible overlay,
and specially designed stress/strain absorbing membranes have all been tried to provide a layer
capable of absorbing the movement of the underlying rigid pavement without transmitting it to the
asphalt concrete overlay surface. These have given mixed results, and some systems are
proprietary.
(6) Reinforcing: Besides geotextiles, other proprietary reinforcing systems using steel wire
and fiberglass grids to combat reflective cracking are available. These have not been evaluated by
the military.
Military experience has found thicker overlays and in some warm climates geotextiles may help
mitigate but not prevent reflective cracking in flexible overlays. Sawing and sealing above the rigid
pavement joints has also been found to be a pragmatic way of minimizing the problems with
17-13
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