Civil Engineering Reference
In-Depth Information
Prestressed high-strength concrete poles that have experienced some
form of cracking can experience autogenous healing. This phenomenon
generally occurs when a crack resulting from a temporary excessive load
that has been applied and released appears in the concrete. In the presence
of newly introduced moisture, the unhydrated cement in the high-strength
concrete creates a paste and seals the crack, protecting the internal steel
reinforcements. Once autogenous healing takes place, the resulting bond
is normally as strong or stronger than the original concrete in that area.
Concrete Repair
The repair area should be totally cleaned by removing loose concrete
and debris. Any exposed steel should be cleaned of dirt, grease, and rust
so that it may be properly coated to protect against corrosion. The concrete
patching material should have nonshrink characteristics and approxi-
mately the same thermal expansion coeffi cient and similar color as the
pole concrete. The repaired area's surface should match the surface level
and contour of the pole. Care should be taken to follow the product
manufacturer's specifi cations. The worker or inspector should verify that
the material and ambient temperatures are within the allowed range
declared in the product specifi cations.
Repair of Surface Voids:
Examples of surface voids are small cavi-
ties, honeycomb, seam leaks, or other small pits. A small cavity is not
larger than 1 in. in diameter nor deeper than 1/4 in. and has no exposed
internal steel reinforcing. All loose or unsound material in the area of the
void should be removed. Next, the area to be repaired should be cleaned
and washed with water to remove all remaining dust and other foreign
particles and then allowed to dry. A thin coat of the bonding agent should
be applied to the area to be patched and allowed to dry. Next, the fi ll
material should be prepared as specifi ed by the Purchaser. Typical fi ll
materials include mortar mixes, grout mixes, a low viscosity epoxy, or
grout/bonding agent compounds. All mixes and compounds should be
prepared in accordance with the product manufacturer's specifi cations.
The fi ll material should be carefully applied to the prepared patch area.
The outside surface of the patch should be leveled, usually with a steel
trowel or sponge fl oat, and possibly sanded smooth after curing. The
resulting patch should follow the contours of the pole's appearance prior
to the damage.
Large cavities (approximately 1 to 6 in. long) should be repaired by
opening the cavity sides to approximately a 1 to 1 slope, at a minimum.
All unsound material should be removed. Typically this is accomplished
with a chipping hammer, chisel, sandblaster, or a mechanical grinder.
Next, the area should be thoroughly cleaned and washed with water to
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