Over the next year and a half, Caltrans plans to jolt new life into Big Sur’s historic Big Creek Bridge, essentially turning it into a big battery.
The process, called electrochemical chloride extraction, works by zapping structures with electricity, pulling out the salty ions that can penetrate concrete and rust a bridge’s inner steel skeleton. Though the process is more common in areas where roads are frequently de-iced with salt, Caltrans demonstrated its ability to use the process to reverse corrosion caused by salt and fog with the rehabilitation of Malpaso Creek Bridge on Highway 1 in 2015.
“Basically, we reset the clock on the conditions that were causing corrosion,” says Kelly McKinley, the Big Creek Bridge project engineer. “It’s like 1932 all over again.”
Like many of the historic bridges in Big Sur, Big Creek is a concrete arch bridge that was constructed during the New Deal in the 1930s. Its historic designation, paired with its location over protected lands below, are two complicating factors for traditional repairs or replacement.
“I wouldn’t even know where to begin to even consider replacing it,” says David Galarza, a structures representative for Caltrans. “It’s probably a multi-year process just to get the permits.” Instead, he says, this procedure will take a year and a half and cost about $10.5 million, with the contract awarded to Arizona-based Truesdell Corporation. Galarza says the high price tag is largely because subcontractor Vector Corrosion Technologies is the only company in the world with the expertise to perform electrochemical chloride extraction.
Truesdell will repair the bridge’s surface concrete that’s become rough and pitted over its 90 years, which will reduce traffic to a single lane during work hours until March or April of 2020. Once Vector initiates its phase of the project, it will seem like business as usual on top of the bridge.
Hidden below, two diesel generators will pump electricity for 24 hours a day through layered titanium mesh and water, all contained within heavy-duty plastic wrap. The generated electricity will pull the chloride ions toward the surface of the concrete, where they’ll dissolve into the water.
If the process is successful, McKinley says it will be applied to more Big Sur bridges, including Granite Canyon, Rocky Creek and Bixby Creek over the next decade.
Galarza says that Caltrans will do everything they can to prolong the life of these bridges.
“They’re beautiful and they’re historic,” he says. “It’s certainly more cost effective to keep them in operation than to consider replacing one.”