Abstract
In an investigation in progress, reinforced concrete test specimens cut from two different sources of concrete culvert pipe were tested under cyclic saltwater ponding and under constant exposure to seawater. The specimens were electrochemically monitored over 700 days (cyclic test) and 400 days constant exposure for evidence of corrosion initiation and measurement of resulting corrosion rates. Corrosion initiation took place after a few months of exposure in the cyclic ponding tests. The corrosion was localized and developed at regions where the concrete cover was lowest (but still within a range consistent with manufacturing practice). Corrosion rates after initiation in the affected spots were estimated to be sufficient to cause concrete cover deterioration after a few years. No corrosion initiation took place after 400 days of continuous exposure to simulated seawater. Near-surface chloride concentrations were much higher in the concrete exposed to cyclic ponding than in that continuously exposed to salt water. Within each exposure regime, the concrete containing fly ash developed a higher near-surface chloride content than the OPC. The apparent chloride diffusivity of the OPC concrete was greater than that of the concrete containing fly ash, even though the reported total binder content of the OPC concrete was higher. The average estimated threshold chloride concentration under cyclic ponding conditions for fly ash containing concrete was ~ 0.6% of binder content. For OPC concrete it was ~ 0.34% of binder content, but the latter value may be underestimated since stable corrosion initiation in the OPC concrete was not observed.
