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Award of Merit: Special Projects Category

Mill Cove Transmission Line Tower Pilings Repair
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Jacksonville, Florida

Submitted by BASF Corporation—Building Systems

Mill Cove

Jacksonville, Florida

Project Engineer/

Jacksonville, Florida

Repair Contractor
Madcon Corporation
Pearl River, Louisiana

Material Supplier/

BASF Corporation—Building Systems
Shakopee, Minnesota

Originally constructed in the 1960s, the Mill Cove Transmission Line consists of 222 pilings supporting seven high-voltage transmission towers. Two towers are located on the St. John’s River and the other five reside in Mill Cove, which feeds into the St. John’s River.

The four corners of the towers are built on concrete piers supported by 10 in. (254 mm) H-pilings. The support pilings were originally encased with concrete from the underside of the pier down below the water line for 14 ft (4.3 m). Over time, the elements in Mill Cove caused the concrete pier encasement on many of the pilings to crack, allowing moisture and oxygen to reach the H-piling, resulting in corrosion and loss of section. Repairs were required both underwater and above the water line.

The pilings were repaired using an epoxy grout encapsulation process to arrest the deterioration of the remaining concrete and the corrosion of the steel H-piling. The pilings were prepared with grit blasting or high-pressure water blasting, followed by the installation of the fiber-reinforced polymer encapsulation jacket. An epoxy grout was then pumped into the jackets from the bottom, using specifically designed plural-component grout-handling equipment. The project entailed several different repair types. Because each repair was unique, a team of specialists created a custom-designed repair solution for each scenario.

The repairs of the towers in the St. John’s River were relatively easy and easily accessible to the divers. The towers in Mill Cove presented some unique challenges due to the shallow water and tidal range. At high tides, the towers were accessible, but at low tides, the Mill Cove area became a mud flat in most areas, making it impossible to navigate.

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