15 March 2001
removed. Occasionally, what appears to be spalling at the surface will actually extend through
the full-slab depth or for more than one-half the slab thickness.
Partial-depth repair should not be tried at such locations. The area should be marked and
full-depth repair accomplished. Full-depth repair should also be made if the concrete below
one-half the slab depth is damaged during chipping or if dowel bars or reinforcing are
encountered during removal. Steel that is encountered in spall areas must be completely
exposed for 1/2 inch (13 millimeters) cleaned and reembedded in the patch material. Under no
circumstances should partial-depth repair material rest upon dowel bars or reinforcement.
5.5. Cleaning. Prior to patching, the exposed faces, bottom of the patch area, and any exposed
steel should be sandblasted to remove all loose particles, oil, dirt, dust, asphaltic concrete, rust,
and other contaminants. As a minimum, air blow, wash with high-pressure water, and air blow
again (Figure 5.6.). The prepared surface must be checked prior to placing the new patch
material. Any contamination of the surface will reduce the bond between the new material and
the existing concrete.
5.6. Joint Preparation. When placing a partial-depth patch adjacent to any joint, there must be
no bond of the repair patch to the face of the adjacent concrete.
Elimination of bond can be accomplished by using a compressible insert (styrofoam, asphalt-
impregnated fiberboard (Figure 5.7.), and plastic joint inserts are commonly used) along the joint
prior to placing the patch material. Patches that abut working joints or cracks that penetrate the
full-depth of the slab require a compressible insert or other bond-breaking medium to reform the
joint or crack. This will form a uniform face against which the joint or crack can be properly
sealed and will separate the patch from the adjacent slab. The new joint should be not less than
the same width as the existing joint or crack. Failure to reform the joint or crack as described can
result in point bearing and failure by blowup, delamination, or new shear planes sometimes in the