Influence of Potential, Chlorides, pH, and Precharging Time on Embrittlement of Cathodically Polarized Prestressing Steel

Corrosion of prestressing steel in concrete has become a major technological problem in highways, buildings, and pipeline structures. While cathodic protection is recognized as an appropriate technique to mitigate corrosion of reinforcing steel in concrete, the possibility of environmental cracking (hydrogen embrittlement) in the case of prestressing tendon has limited application to this usage. To establish the appropriateness of cathodic protection for prestressing steel, constant extension rate testing was performed on smooth and notched wire specimens in deaerated Ca(OH)₂ solutions as a function of potential, [Cl⁻], pH, and precharging time. Results indicated potential is the most important of these variables, and a threshold value of –0.90 V_SCE was identified below which embrittlement is enhanced. Notched specimens, which may best simulate the geometry of corroded tendon, particularly were susceptible when compared to smooth tendon. Failure of some tendons in this condition could occur upon application of cathodic protection, even when potential is positive to –0.90 V_SCE. Other aspects of cathodic protection utility for prestressed concrete are reviewed.