Kingsley Lau

Corrosion performance of concrete cylinder piles

Abstract Posttensioned concrete cylinder piles produced using 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. The older marine bridges showed minimal corrosion distress despite a low design concrete cover over the steel hoop reinforcement (2 cm to 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 1 × 10−9 cm2/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 chlo...

Service Life Forecasting for Reinforced Concrete Incorporating Potential-Dependent Chloride Threshold

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. An innovative model to predict corrosion in reinforced concrete structures is presented, incorporating potential dependence and corrosion macrocell effects. The novel approach integrates the initiation and the propagation stages of corrosion in a single predictive model. The model is applied to a generic, partially submerged, reinforced concrete marine pile. The purpose of this paper was to establish and illustrate the concept of a functional approach to implement potential-dependent chloride threshold in corrosion damage projections, plus articulation of the initiation and propagation stages, in one predictive model. The long-term damage projection results are markedly lower contrasted with those of an identical system with a time-invariant chloride threshold. The results show that implementing chloride threshold depende...

Corrosion Of Epoxy- And Polymer/Zinc- Coated Rebar In Simulated Concrete Pore Solution

Abstract This work is an initial examination of mechanistic issues on the comparative corrosion performance of regular epoxy-coated rebar (ECR) and dual polymer-zinc-coated reinforcement (DCR) in simulated concrete pore solution with and without chloride ions, at polarizations from 100 mV to −1,000 mV in the saturated calomel electrode (SCE) scale and exposure periods of 1 month or longer. Both materials had intentional coating breaks exposing the base steel. Polymer adhesion degradation of DCR relative to the as-received condition was comparable to, or less than, that experienced by ECR under both anodic and cathodic polarization and with and without chloride ions. Both DCR and ECR experienced severe corrosion at breaks under strong anodic polarization with chloride ions, but distress for DCR was significantly less than for ECR. Under open-circuit conditions DCR experienced an initial high-activity period both in the presence and absence of chloride ions after which the open-circuit potential (OCP) stabi...

Coating Condition Evaluation of Epoxy Coated Rebar

The initial results of ongoing research on the corrosion condition of epoxy coated steel reinforcement (ECR) from a low permeability concrete marine structure with thin preexisting structural cracks after ~20 years of service are presented. Coating autopsies and electrochemical impedance spectroscopy measurements were conducted on ECR samples extracted from the field. No preferential coating deterioration was observed on ECR zones intersected by a crack compared to the rest of the ECR segment. Results from EIS measurements show a high frequency (hf) loop in disbonded ECR samples. Larger hf loops in cracked concrete samples are indicative of larger electrolyte conductance. The low frequency impedance response behavior is characteristic of current and interfacial capacitance distribution in a transmission line configuration. Further tests are in progress.

Corrosion of Post-Tensioned Tendons with Deficient Grout, Part 1: Electrochemical Behavior of Steel in Alkaline Sulfate Solutions

Severe corrosion recently documented in Florida post-tensioned bridges were related to grout segregation that created deficient grout with characteristics of having low chloride content, high sulfa...