Concrete cylinder piles produced by a centrifugally cast, vibrated, roller-compacted process have shown promising corrosion resistance in marine environments. Three bridges in the Florida panhandle with ~40 years in aggressive marine service and one newly constructed marine bridge utilizing concrete cylinder piles were examined. Examination of the older marine bridges showed minimal corrosion distress despite low design concrete cover over the steel hoop reinforcement (2-4 cm). Typical concrete distress included minor rust staining (not necessarily indicating corrosion of reinforcement steel) and thin longitudinal cracks (likely caused by mechanical damage from pile driving). Chloride ion diffusivity was low, in the order of 1x10 -9 cm 2 /s. Other measured parameters such as concrete resistivity, porosity, and water absorption indicate low permeability. Chloride analysis of cracked and uncracked concrete cores from the older bridges in this study did not show pronounced preferential chloride penetration. Chloride analysis from the contemporary marine bridge did show some preferential transport of chloride ions at shallow depths through cracks with further evidence of lower electrical resistivity indicating enhanced electrolyte transport. Simplified corrosion durability modeling projections indicate that a moderate relaxation of a current 7.6 cm cover requirement may be made without significantly compromising the service life requirements of cylinder piles.

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The chloride corrosion threshold of steel in concrete depends not only on concrete and steel properties but also on the potential of the steel while it is still in the passive condition. A deterministic model to predict corrosion in reinforced concrete structures is presented, incorporating potential dependence and corrosion macrocell effects, resulting in coupling of the corrosion initiation and propagation stages. The model is applied to a generic partially submerged reinforced concrete marine pile. An analysis is made of sensitivity of model output to input parameters including the rate of dependence of threshold on potential, concrete resistivity, oxygen diffusivity and size of the steel zone activated upon reaching the chloride threshold. The results are contrasted with those of a comparable system where the threshold is not potential dependent.

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Corrosion failure of post-tensioning (PT) tendons with pre-packaged thixotropic grout has been documented in Florida bridges. Analysis of the deficient grout in Florida PT bridges, where severe corrosion developed, indicated elevated sulfate ion concentration, high pore water pH, low chloride ion content, and enhanced moisture content. Limited information is available on the corrosion behavior of PT strand in grout materials with elevated sulfate ion content. In this work, the corrosion performance of steel strands embedded in deficient grout was evaluated. The deficient grout was cast in large scale test assemblies that would represent geometry and material conditions found in Florida bridges, where PT strand corrosion occurred. Large scale mock up tendons (developed by the modified inclined tube [MIT] test) of about 4.57 m long were cast using expired grout materials, excess of 15% water, and sulfate ion concentrations to create deficiencies and corrosion conditions in the grout environment. Corrosion measurements such as corrosion potential (Ecorr) and corrosion current density (icorr), as well as potentiodynamic polarization tests were performed on the steel probes located along the MIT samples in contact with the deficient grout. Grout characterization parameters included the determination of the grout resistance (Rs), as well as the moisture and sulfate ion content. Also, visual inspection of the MIT samples (steel strand and steel corrosion probes) after a time was performed, as well as the corrosion products characterization. Testing confirmed that enhanced corrosion can occur in the deficient grout with high free sulfate ion accumulation.