Jacksonville Electric Authority/Florida Power & Light Company operates two coal fired 640 MW power plants at the St. Johns River Power Plant in Jacksonville, Florida. Corrosion related damage to Unit #2 Natural Draft Cooling Tower had progressed to the point where structural integrity and safety was a concern. The tower was built in 1985 (at a cost of over $50 million) and is 450 feet high and 320 feet in diameter. Existing Structures Engineering, Inc. (ESE) was hired to perform an engineering condition survey coupled with recommendations, and repair/remediation design. The scope of the project ultimately grew to include construction engineering and inspection.
The restoration project was accomplished in 3 phases: detailed condition survey and recommendations, restoration/corrosion control research and design, and construction with the goal of avoiding replacement of the structure. The condition survey was designed to quantify the scope of repairs and determine the root cause of corrosion, and the reasons for the poorly performing corrosion control actions previously taken. The research and design phase involved a review of existing technologies and demonstration testing of innovative technologies. A repair/cathodic protection zinc mesh jacket system was selected for the tower’s legs and lintel ring beam (18,000 ft2). The veil (58,000 ft2) presented unique challenges due to height and proximity to in-use services. The selected system: robotic ultra high pressure water demolition for removal of deteriorated concrete, machine applied application of repair mortar, application of zinc mesh, and a final application of shotcrete to encapsulate the zinc mesh. The resulting system provides a combined repair process and cathodic protection of the embedded reinforcement, estimated to protect for more than 2 decades without further maintenance actions.
This project recently won the Grand Award in the 2007 Florida Engineering Society Engineering Excellence Awards Program, the ICRI 2007 Award of Excellence, and the American Shotcrete Association 2006 Outstanding Shotcrete Project Award.