Marker Name: Cathodic Protection - Saving Oregon’s Gems
Marker Text: Oregon was literally pulled from the mud by a statewide boom of road construction projects in the 1930s. Many of the most admired bridges along the coast were constructed during this era. Several of these historic steel-reinforce concrete structures are suffering from prolonged exposure to marine salts. Salt present in the coastal environment has slowly migrated through the concrete and is causing corrosion of the bridge’s steel reinforcement (rebar). Corroding rebar swells, slowly causing the concrete to crack, compromising the bridge’s structural integrity. Rather than allowing these architectural treasures to become a thing of the past, Oregon Department of Transportation (ODOT) is restoring and protecting them for the future.
The Rocky Creek bridge is one of several rehabilitated bridges along the Oregon coast. Other coastal bridges that are being (or have been) restored are: the Yaquina Bay Bridge at Newport, the Depoe Bay Bridge, the Cape Creek Bridge and the Rogue River (Isaac Lee Patterson) Bridge in Gold Beach.
The Cathodic Process - An electrifying battle!
ODOT is addressing the problem of corrosion in Oregon’s historic bridges with a process called cathodic protection.
When Oregon’s coastal bridges were built (1920-40s), engineers were not aware that marine salts would have a devastating effect on bridges. Over time, salt corroded rebar expanded, causing surrounding concrete to crack and fall off. ODOT is restoring historic bridges by repairing damage and protecting the structure from future salt damage.
The process begins with construction of a containment enclosure, which controls atmospheric conditions and contains construction debris.
Next restoration starts on the bridge, Damaged concrete is removed, exposing corroded rebar.
Rebar is repaired and connected in order to make an electrically continuous circuit before being covered with new concrete.
A zinc coating is applied to the concrete surface.
A low voltage electrical current is passed through the rebar. This causes the zinc coating to protect the rebar from corrosive salts -- the zinc coating will experience corrosion but the rebar will not!
The zinc may need to be replaced in 25 to 30 years, but the concrete and rebar should last indefinitely without repetition of the concrete and rebar repairs.
Finally, sensors are placed on the bridge and linked to a computer that allows ODOT to monitor the changes in electrical energy levels. The electric energy is maintained at an appropriate level to protect all areas of the steel.
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