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Section 4: Prestressed Concrete Piling

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Description

This section includes limits and repair procedures when assessing damage to prestressed concrete piling.

This section also includes a procedure to recess and coat lifting strands after installation of piling.

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Reference

Standard Specification Item 409, “Prestressed Concrete Piling.”

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Notes

Piling damage is divided into two categories: (1) damage that occurs prior to driving (during fabrication, handling, storing, or hauling), and (2) damage that occurs during driving operations (lifting or driving). When assessing damage to exposed portions of prestressed piling in an existing structure, treat it as a typical concrete substructure element. No special limits apply.

The acceptance and rejection criteria for prestressed piling are more severe than with most other structural elements because the consequences of a failure are also very severe. Foundation distress is typically very difficult to remedy and can lead to shortened service life of an entire bridge. Therefore, damage that could potentially hinder performance or reduce durability will typically lead to rejection of the piling.

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Damage Prior to Driving (e.g. in the Fabrication Yard)

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  • Minor damage.
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    • Only thin spalls may be repaired. The Engineer will determine what constitutes an acceptable spall, but in general the limits are 1-inch in depth and 6 square inches in area. If either of those limits is exceeded, or if the damage exposes any reinforcing steel or prestressing strand, the damage will render the piling unacceptable unless specifically deemed otherwise by the Engineer.
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    • Smooth out the perimeter of the damaged area to eliminate jagged edges.
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    • Minor spalls deemed acceptable for repair should be cleaned and coated with neat epoxy in accordance with Section 1 of Chapter 3 of this manual.
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    • Do not build up the spalled areas with repair material other than neat epoxy since it is likely to debond during driving operations.
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    • The Engineer may allow for repair when damage is deeper than 1 inch but does not progress beyond the outer layer of steel reinforcement. In those cases the damaged areas should be built up with epoxy mortar and confined by CFRP wrapped completely around the piling for a distance not less than six inches beyond the damaged area.
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  • Damage to one end.
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    • If one end of a piling is damaged beyond the limits outlined above, but the damage extends less than 6 inches from the end, then the fabricator or contractor may remove (cut) up to 6 inches from the end to eliminate the damaged portion.
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    • Clearly mark the altered side as the “Tip End.”
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    • After cutting, recess the prestressing strands 3/8-inch minimum and fill the voids with epoxy mortar (typical strand end treatment).
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    • Re-form the chamfers after completing the cutting and repairing operations.
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  • Damage to both ends.
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    • There are no standard criteria for acceptance or rejection when both ends of a piling are damaged, but generally the member will be rejected since it would not be possible to avoid hammering a damaged end.
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    • Engineer must approve any repairs when damage occurs on both ends of a piling.
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Damage During Driving

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  • Horizontal cracks (transverse to longitudinal reinforcement or strand) greater than 1/16 inches wide.
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    • Piling will be rejected if crack occurs in a portion that will be below ground or water level after driving.
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    • If crack occurs in a portion that will be above grade or water level, the Contractor may opt to cut back beyond the crack and rebuild to required elevation.
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  • Horizontal cracks less than 1/16 inches wide.
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    • Inject the cracks with epoxy in accordance with Section 3.7 of this manual.
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    • If cracks develop that will be inaccessible in final configuration, cease driving operations and repair cracks before continuing.
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  • Vertical or diagonal cracks.
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    • In most cases a piling member will be rejected if vertical or diagonal cracks form during driving operations.
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    • If the Engineer approves repair of vertical or horizontal cracks, inject with epoxy in accordance with Section 3.7 of this manual.
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  • Fine hairline cracks (less than 0.006 inches) or surface checks that do not extend to the plane of the nearest reinforcing steel will not require repair and will not be cause for rejection.
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Lifting Strands

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  • Recess lifting strands to help prevent corrosion due to exposure to the elements.
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    • Recess the prestressing strands a minimum 3/4-inch using a torch, grinder, or other approved method. Do not overheat or damage the surrounding concrete.
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    • Abrade the concrete and the end of the steel strand with a needle gun, steel brush, or other suitable means to ensure that no slag remains on the steel or concrete surfaces.
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    • Coat the inside of the recessed area, including the strand, with 10 mils (minimum) of neat Type VIII epoxy and repair the recess with epoxy mortar.
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