Electrochemical Characterization and Acoustic Emission Monitoring of Corrosion in Prestressed Concrete Piles

Concrete bridge superstructures in coastal regions are often supported by prestressed concrete (PC) piles. At the splash zone, PC piles are exposed to a steady supply of moisture, oxygen and chlorides, an environment that may sustain high corrosion rates on multi-wire prestressing strands. In PC piles, corrosion is a major concern because the concurrence of tensile stresses and corrosion may lead to strand fracture before visual inspection uncovers signs of damage, and well before the end of the design life. Predicting corrosion initiation and recognizing corrosion in its early stage are critical to plan maintenance and repairs and prevent premature failures. Experimental corrosion studies were conducted to quantify early corrosion parameters and develop criteria for detection and assessment on PC piles exposed to tidal action. The effects of strand geometry and axial stress on the critical chloride concentration of prestressing strands were investigated in simulated pore solution immersion tests. PC pile specimens were exposed to simulated tide and monitored with open-circuit potential and polarization resistance measurements to study the feasibility of a criterion for corrosion detection based on the polarization resistance. The specimens were monitored continuously with acoustic emission (AE) sensors to investigate the feasibility of using AE as an early corrosion monitoring technique. Crevice action was found to cause a significant reduction of the critical chloride concentration of strands with respect to corrugated bars, and pulling the strands was observed to produce further chloride threshold reductions. Polarization resistance data from strands in pore solution showed that corrosion rates during early corrosion are higher on strands than on corrugated bars. Measurements of polarization resistance on PC piles showed that corrosion can be assessed based on polarization resistance thresholds. AE intensity analysis of data from the PC pile specimens showed a clear distinction between corroding and non-corroding specimens, thus offsetting the inadequacy of traditional AE parameter analysis. This feature was used to preliminarily define criteria for early corrosion assessment of PC piles based on AE monitoring data