Abstract
Commercial ductile iron post-tension anchorage assemblies containing unstressed high strength strand, two types of grout and simulated grout voids were subject to simulated water intrusion events with fresh and salty (0.01N NaCl) water. Galvanic current, strand-anchor conductance and potentials were monitored to identify corrosion location and magnitude. Potentials of the galvanic systems at different locations along the assemblies were recorded. The results from showed that external water intrusion can be a major source of corrosion tendon failure. Conditions for strand steel depassivation can develop even if only modest carbonation of the grout occurs. Fresh water could initiate corrosion if the native chloride content of the grout exceeded a relatively small amount (e.g. 500 ppm). Currently allowable chloride limits may need revision. Galvanic coupling between strand steel and anchorage iron could significantly aggravate corrosion of the strands. Significant corrosion of strands in the void space was observed, especially in a grout that supported high internal relative humidity. Projections of the combined effects of the deterioration mechanisms identified were consistent with the observation of tendon failures in the field after as little as 7 years.
