Abstract
A case study detailing the condition assessment of a three-level underground parking garage, this paper describes the technical challenges involved with evaluating corrosion in a structural slab beneath a thick, unbonded overlay.
The investigation of this structure was part of a major renovation and vertical expansion of a high-rise building in Manhattan. Originally constructed in 1953, the parking decks exhibited substantial corrosion and spalling damage on the slab soffits including many previous failed repairs. The top of slab condition was covered by a 4-inch thick cementitious overlay. Sounding and core extraction indicated that only approximately 30% of topping slab was bonded to the structural slab. Since material testing indicated substantial chloride contamination in both the topping and structural slabs, the condition of the top-layer of reinforcing, particularly the negative moment steel around the columns had to be understood. The inconsistent void between slabs interfered with the results of traditional corrosion potential and corrosion rate measurements.
When wide spread issues provide challenges to the field engineers it is vital to understand how to interpret the findings. When structures appear to be in good conditions owners often are not sold on the idea of spending money on investigation. In this instance the client was proactive and instead of relying on a number of cores to make decisions employed corrosion professionals to evaluate the condition within the slab. This paper describes how these challenges were overcome in order to establish the condition and safety of the structural slab as well as design and implement durable repairs.
