Post-Tensioned Floor Slab Corrosion Failure

An apartment building in Melbourne was constructed in 1995, with post-tensioned floors and beams, and with in-situ reinforced columns to form the two parking basement levels and 13 above ground storeys. The ground floor slab inside the building was used as the base slab for a swimming pool, with the pool walls constructed in reinforced concrete connected to the post-tensioned floor slab. 

Leaking of chlorinated pool water over many years was not detected due to the hidden cavity adjacent to the pool, with the resultant corrosion to all floor slab tendons and some beam tendons over an approximately 15m x 20m area of the ground floor slab. Structural assessment could not determine why the slab did not collapse into the basement levels. 

The paper describes the extensive investigation of the extent of strand corrosion and concrete damage to the slab and beam. The repair design is also described, which includes temporary propping of the slab, strand removal and concrete repair, impressed current cathodic protection to post-tensioned beams and pool walls, structural steel support to the slab and waterproofing of the pool and surrounds.