UFC 3-260-02
30 June 2001
CHAPTER 17
OVERLAY PAVEMENT DESIGN
1. GENERAL. Overlay pavements are designed to increase the load-carrying capacity (strength)
of the existing pavement. The basis for design is to provide a layer or layers of material on the
existing pavement that will result in a layered system which will yield the predicted performance of
a new rigid pavement if constructed on the same foundation as the existing pavement. Two
general types of overlay pavement are considered: rigid and nonrigid. Procedures are presented for
the design of plain concrete, reinforced concrete, continuously reinforced concrete, fibrous
concrete, prestressed concrete, and nonrigid overlays. Nonrigid overlays include both flexible
(nonstabilized base and bituminous concrete wearing course) and all-bituminous concrete for
strengthening existing plain concrete, reinforced concrete, and flexible pavements. Continuously
reinforced, fibrous, and prestressed concrete overlays will not be permitted unless it is technically
and economically justified and approved by HQUSACE (CEMP), Air Force Major Command, or Naval
Facilities Engineering Command. Overlays will be used when the nonstabilized aggregate base
course can be positively drained. When the overlay includes a nonstabilized aggregate base course
layer, the unbound base course must be positively drained.
2. CONVENTIONAL OVERLAY DESIGN EQUATION BACKGROUND AND LIMITATIONS. The
overlay design equations for rigid and flexible overlays of rigid pavements presented in this chapter
are based on full-scale accelerated traffic tests conducted in the 1950's modified with experience
and performance observations in succeeding years. The equations were developed to support a
program of strengthening Air Force airfield pavements to accommodate the introduction of the
large B-47 and B-52 aircraft into the inventory. Because of theoretical limitations of the time, the
overlay equations are empirical. They have the advantage of simplicity for use, but their empirical
basis means that they are valid only for conditions consistent with their original development. To
use these equations effectively, one must be aware of their limitations and their proper application
as discussed in this chapter. For more complex situations, a more comprehensive overlay analysis
as presented in the layered elastic design chapter may be necessary.
a. The overlay equations for rigid and flexible overlays of rigid pavements recognize four basic
conditions:
(1) Fully bonded overlay where the rigid overlay and rigid base pavement are fully bonded
and behave monolithically. Because of problems with providing load transfer, these overlays are
generally limited to correcting surface deficiencies of a structurally adequate pavement in good
condition other than the surface problems.
(2) Partially bonded overlay where no particular attempt is made to achieve or prevent
bond between the rigid overlay and the base pavement. This equation is a best fit to empirical data
and therefore can give either conservative or nonconservative thicknesses. Partially bonded
overlays are particularly well suited for structurally upgrading an essentially sound pavement to
accommodate larger loads as might happen when a mission change brings new heavier aircraft to a
base.
(3) Unbonded overlay where a thin separation layer asphalt concrete or other material is
interposed between the rigid overlay and the base pavement to avoid direct bonding between the
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