Concrete aeration tanks play a critical role in production at paper mills by treating and disposing of pulp waste. It’s important to maintain these structures through regular inspections and proactive repairs.

A West Coast paper mill had a concrete aeration tank that was showing signs of distress. The tank, 33 feet in height and 235 feet in diameter, had multiple prestressed cables failing and spalling concrete due to environmental exposure and the age of the structure.

The client was interested in STRUCTURAL’s partnership with STRUCTURAL TECHNOLOGIES and the innovative, cost-effective solution presented using the Investigate-Design-Build (IDB) process.

After STRUCTURAL TECHNOLOGIES performed a condition assessment, they worked with the owner and developed a solution that would meet schedule and budget requirements. The final design of the repair included addressing the prestressed cables and installation of carbon fiber-reinforced polymer (CFRP) on the interior of the tank to strengthen the existing concrete.

During the initial phase of the project, the STRUCTURAL team noted the condition of the concrete substrate following surface preparation was worse than anticipated. Because the project was design-build, the team was able to rapidly assess and develop an enhanced approach factoring in the unforeseen conditions. This challenge was overcome without impacting the project’s overall schedule.

The scope of the project included removal and installation of 32 new external PT tendons and repair of the impacted concrete around the cables. Along with this approximately 12,000 square feet of carbon STRUCTURAL then performed surface prep on the internal walls followed by 12,000SF of CFRP was installed on the interior of the tank, along with a protective coating. The project was safely completed on schedule during a single plant shutdown, which minimized downtime for this critical tank.