Prestressed Concrete Piles Cathodic Protection Pilot

A multi-span bridge has seven prestressed octagonal piles providing support to the reinforced concrete pile caps, where the piles are fully submerged in the marine environment. The submerged piles are suffering from alkali-silica reaction (ASR) instigated cracking, exposing the spiral ligature and prestressing strands to ongoing corrosion. As an alternative to long-term repetitive repairs by divers, a pilot cathodic protection (CP) system was designed and installed to one of the pile caps and the seven prestressed piles to control future corrosion.

The paper describes the pile arrangement and the basis of the Galvanic CP design and design assumptions, photographs and details of the installed pilot CP arrangement, including four aluminium anodes, negative connections and two reference electrodes. The CP system was connected to a remote monitoring system, with readings taken at two-hour intervals during the polarization stage, allowing the galvanic anode currents and instant off potentials to be recorded.

The prestressed reinforcement in the piles polarized to between -800 to -860 mV Ag/AgCl/0.5M KCl providing a safe level of protection and avoiding hydrogen embrittlement polarization levels of less than -900mV Ag/AgCl/0.5M KCl. The data obtained via the remote monitoring system permits the design assumptions to be directly compared to the actual system performance, allowing the design life of the system to be reviewed prior to the full-scale design for the remaining pile caps and piles of the bridge.