AWARD OF EXCELLENCE: Longevity Category

REHABILITATION OF TWO HYPERBOLIC COOLING TOWERS

Washingtonville, Pennsylvania

Submitted by CTLGroup

Two hyperbolic concrete cooling towers serving a steam electric generating station were put into service in 1972 and 1973. By 1985, they exhibited significant deterioration, corrosion of embedded steel, and water leakage through the shells. These massive towers, which topped out at 370 ft above grade and were as large as 248 ft in diameter, were essential to the plant’s operation. They would need major repairs, which could be carried out only during scheduled outages to avoid disruptions in the area’s power supply.

Scheduling repairs was only one of the project’s challenges. Providing access to the interior and exterior of the towers to allow thorough inspection and repair was difficult. Careful structural analysis was required to maintain the towers’ structural integrity while repairs were under way. Repair materials had to be evaluated and selected for their ability to withstand the unusual conditions within the towers.

To meet these challenges, the power company assembled a multidisciplinary team made up of both staff and consulting engineers. The team included civil engineers, concrete material and construction consultants, structural engineers, and specialists in testing and evaluation.

Using visual inspection, hammer sounding throughout both towers, and laboratory testing of core samples, investigators identified the types and extent of concrete deterioration. In addition to the spalling, corrosion, and leakage already noted, they found cracks in the support columns and ring beams at the bases of the towers.

Repair crews removed the deteriorated concrete from the tower shells with pneumatic chipping hammers and filled the created voids with dry-mix shotcrete. They sealed cooling tower interior surfaces with a water- and vaporproof epoxy coating. They cleaned out cracks in the supporting columns and ring beam and sealed them with epoxy.

Meticulous quality control testing and inspection during repairs helped ensure the project’s success. The work accomplished between 1988 and 1990 has demonstrated its durability and significantly extended the towers’ service life.

Owner
PPL Corporation
Allentown, Pennsylvania

Project Engineer/
Designer
CTLGroup
Skokie, Illinois

Kline Engineering, PC
Port Washington, New York

Repair Contractor
Pullman Power
Kansas City, Missouri

Material Supplier/
Manufacturer
Sika Corporation
Lyndhurst, New Jersey