UFC 3-260-02
30 June 2001
and special efforts are made to obtain bond. The partially bonded condition is obtained when the
concrete is cast directly on concrete with no special efforts to achieve or destroy bond. The
nonbonded condition is obtained when the bond is prevented by an intervening layer of material.
When a fully bonded or partially bonded rigid overlay is to be used, the existing rigid pavement will
be cleaned of all foreign matter (such as oil and paint), spalled concrete, extruded joint seal,
bituminous patches, or anything else that would act as a bond-breaker between the overlay and
existing rigid pavement.
(1) In addition, fully bonded overlays use careful surface preparation to ensure the overlay
and underlying base slab are fully bonded and behave monolithically. To reliably achieve this full
bond, the base slab is cold milled or shotblasted to remove all deteriorated or defective concrete
and all surface contamination. This roughened surface must be thoroughly cleaned by sandblasting
followed by airblasting, waterblasting, or both. Achieving and maintaining the surface cleanliness
concrete placement is critical for achieving good bond. A portland-cement grout is then
pneumatically applied immediately ahead of the concrete placement to help achieve a high degree
of bond between the new and old concrete. This grout must not dry prior to placement of the
concrete so usually it is only applied about 3 to 4 m ahead of the concrete placement. If the grout
dries out prior to the concrete placement, the grout should be removed by sandblasting or other
similarly reliable method and reapplied prior to continuing concrete placement. Older requirements
for acid etching the base concrete surface are unnecessary and are not environmentally sound.
Portland-cement grouts have proven adequate, and more expensive epoxy or polymer grouts are
not normally needed. Some bonded overlays have reportedly been successfully placed with no
bonding grout, but the military has no experience with such at present. For military airfield work
where debonding poses such a serious FOD hazard, the intense surface preparation, surface
cleaning, and use of a portland-cement grout are considered to be the minimum allowable effort for
fully bonded overlays.
Past tests and studies have failed to identify adequate methods of providing satisfactory load
transfer in fully bonded overlays. Consequently, fully bonded overlays will only be used on military
airfields to correct surface deficiencies, and they are not suitable for structural upgrades unless the
pavement is redesigned assuming no load transfer exists. The minimum thickness for a fully
bonded overlay is 50 millimeters (2 inches), and most military airfield bonded overlays have been
75 to 125 millimeters (3 to 5 inches) thick. Typical past uses have included correction of surface
smoothness or skid resistance problems, providing a sound operational surface over underlying
pavements that are scaling, posing an FOD hazard from popouts or spalling and raveling, or to
cover pavement surfaces that pose an FOD hazard from D-cracking, excess surface grout, or alkali-
aggregate reaction deterioration.
All joints and cracks in the base pavement will reflect through a fully bonded overlay.
Therefore, the overlay joints must match the base slab joints. Cracked slabs in the pavement to be
overlaid should be removed and replaced, or the bonded overlay slab above the cracked slab should
be reinforced.
(2) When a nonbonded rigid overlay is being used, the existing rigid pavement will be
cleaned of all loose particles and covered with a leveling or bond-breaking course of bituminous
concrete, sand-asphalt, heavy building paper, polyethylene, or other similar stable material. The
bond-breaking medium generally should not exceed a thickness of about 25 millimeters (1 inch),
except in the case of leveling courses where greater thicknesses may be necessary. When a rigid
overlay is being applied to an existing flexible pavement, the surface of the existing pavement will
be cleaned of loose materials and any potholing or unevenness, exceeding about 25 millimeters
17-3
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