A chemical plant is home to three rainwater treatment tanks - two measuring 150 feet in diameter and one measuring 122 feet. All three were built in 1992, and all three were of wire-wrapped concrete construction. When a wire-wrapped ring beam corroded and failed on one of the tanks, it was necessary to have it repaired in order for the tank to remain operational.
VSL refined the owner's original concept in order to better align the scope with the desired outcome - a long-lasting solution.
One of the first tasks was accessing the root cause of the deterioration. The engineer determined that a joint above the beam in the tank had leaked, allowing water into the concrete behind the beam. The infiltration caused the wires to corrode and fail. When they snapped, the beam fell. Post-tensioning was then specified as the repair method for this structure because it could be applied externally.
The team chose an encapsulated external PT system which passed the Post-Tensioning Institute's (PTI) water tightness test - this included connections that were sealed against water penetration. The system, which was encased in a highly protected UV pipe, was furnished and installed for the failed tank, as well as for the other two tanks as a precautionary measure. Ten strands were installed in 360-degree hoops around each tank. The installation did present a challenge, however, as VSL could not attach the strands using any method that would penetrate the surface because of the tank construction. For this reason, VSL devised a method of attaching the strands with straps before they were stressed and could remain unsupported, which allowed the integrity of the structure to be preserved.
Lastly, a coating membrane was applied at the dome of each tank as a preventative measure to help prevent any further water infiltration or erosion of the ring beams. It was placed on all three domes at the joint where the dome meets the vertical walls of the structure.