Mechanism of Corrosion of Steel Strands in Post Tensioned Grouted Assemblies

In this preliminary study, the complexity of the corrosion phenomenon of post-tensioning strands in grouted anchorage assemblies was examined and both physicochemical and electrochemical key technical issues were identified. Measurements of oxygen reduction efficiency in high pH electrolytes were conducted to obtain polarization parameters to be used in modeling. The time evolution of electrical resistivity of 5 low-bleed commercial grouts was measured also for model input. A mathematical model for a simple grout-strand system was proposed and dimensionless equations were formulated, to solve the combined polarization and oxygen transport problem. Within the range of validity of the model assumptions, initial computations indicated that oxygen availability was a key factor in determining corrosion severity while grout resistivity was secondary. Predicted corrosion rates were in general agreement with field and laboratory observations. Issues for subsequent model development were identified.