Cathodic Protection of Coastal Prestressed Concrete Piles: Prevention of Hydrogen Embrittlement

About the report:

Assessing the effect of cathodic protection (CP) on a chloride-contaminated bridge pile involved defining the hydrogen embrittlement behavior of the pearlitic reinforcement and quantifying the local (i.e., at the steel/concrete interface) chemical and electrochemical conditions, both prior to and throughout the application of CP. The hydrogen embrittlement behavior of the reinforcement was assessed through a combination of Devanathan/Stachurski permeation experiments to quantify subsurface hydrogen concentrations, CH, as a function of the applied hydrogen overpotential, 0, and crack initiation tests for bluntly notched and fatigue precracked tensile specimens employing elastic-plastic finite element analysis and linear elastic fracture mechanics, respectively. A series of laboratory scale piles was constructed to determine relevant environmental and electrochemical conditions at the steel/concrete interface. Laboratory-scale piles were partially immersed in ASTM artificial ocean water and allowed to stabilize. With time, localized corrosion (crevicing) was initiated along the reinforcement and was accompanied by a shift in the pH of the occluded environment from an alkaline pH 12.6 to 5.5 and below due to ferrous ion hydrolysis. CP current densities from 0.1 to 2.5 IJAlcm2 (per unit area reinforcement) were applied via a skirt anode located at the waterline. By combining the effect of local CP level as a function of position along the reinforcement on hydrogen absorption with the information on the hydrogen embrittlement characteristics of the reinforcement as a function of hydrogen concentration, safe windows for the application of CP may be identified. With the exception of 100 mV depolarization/decay criteria, it was not possible to sufficiently protect the splash zone of the pile with its high corrosion rate without exceeding the threshold hydrogen concentration for embrittlement at some zone within the reinforcement.

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