Effectiveness of Surface-Applied Corrosion Inhibitors for Concrete Bridges

While the effectiveness of corrosion-inhibiting admixtures in new concrete has been well documented, there is little research on their surface-applied counterparts for existing structures. This study was undertaken to assess whether surface-applied products can delay, slow, or stop the corrosion process in contaminated concrete. A total of 348 specimens were tested using six commercially available corrosion inhibitors, at six levels of initial chloride content, and under two accelerated corrosive environments of salt-water spray and wet-dry cycles. Half of the specimens were intentionally cracked before applying the inhibitors, while the others were cracked afterward. Corrosion current and half-cell potential readings were taken weekly during the environmental exposure. Corroded bars were then assessed visually for surface rust and rib loss; and their mass loss and strength reduction were measured. Progression of chloride content over time was measured using companion concrete cubes. The inhibitors generally delayed the onset of corrosion and slowed the process, up to an initial chloride content of 0.5% by weight of cement. Each product seemed effective up to an extent in exposure time and the chloride content. However, no product stopped the corrosion process, and none purged chloride ions. The products may be most effective as preventive measures for fully hardened “virgin” concrete with initial chloride content below those specified to induce corrosion.