The bottom steel in the waffle slab of a 23-year-old underground parking structure in Columbus, Ohio was severely corroded in some areas. A trial cathodic protection (CP) system was installed on the top of the parking deck in an attempt to prevent any further corrosion. CP systems are extremely effective at stopping steel corrosion in reinforced concrete structures. They have been used successfully on parking structures, concrete bridge decks, and off-shore concrete structures.
INSTALLING THE BOTTOM-MOUNTED SYSTEM
To provide the current needed to protect the joist steel, a second CP system was applied to the underside of the joists on the parking structure. Work was done in three main steps:
- Bottoms of the joists and column pads were waterblasted under a pressure of 2400 psi.
- Anode strands were attached to the bottoms of the joists and column pads.
- A special mortar was placed over the anode strands to isolate the anodes from the concrete surface and to provide a protective cover.
TESTING SHOWED BOTTOM CATHODIC PROTECTION WORKS
In December 1984, after the top and bottom CP systems were put into use on this parking structure, electrical testing was performed to see whether the systems were effective. The average electrical polarization of both the top and bottom reinforcing steel was found to be above the amount usually thought needed for complete cathodic protection.