Bridge washing 101: A high-pressured process

The hoses come out in the wee hours of the morning last fall as workers prepare to wash the U.S. 30 bridge over Interstate 88 near Rock Falls. After one of the two traffic  lanes are closed, they begin spraying highly pressurized water fed by a tanker truck onto every part of the bridge and finish before the day truly begins.

The work is a patient and coordinated process. There are numerous starts and stops to allow traffic that’s queued up on each side of the bridge to pass. Time is spent addressing each lane of the bridge, including the median, deck, parapet walls, expansion joints, rubber troughs, and drains to adequately clear the bridge of all kinds of muck — salt, bird nests, dirt, droppings and other debris. After the top of the bridge is clean, work moves to spray the bottom of the bridge — the beams, piers and abutments. Then it’s on to the next assignment.

Bridge washings like this happen throughout Illinois during the warmer months for two reasons, says Bridge Design Section Chief Mark Shaffer.

“The first is to remove salt from the bridges, which has accumulated during winter months. Salt will corrode steel beams, and seep into the concrete and corrode reinforcement,” he said. “The second reason is to remove all bird and bat waste from the bridges to ensure that inspectors can properly inspect the bridges. It is not uncommon for flanges of bridges to be covered in nests and waste, making it very difficult for the inspectors to be able to find corrosion and damage.”

Bridge washing requires no detergents, just water and specialized equipment.

“Contractors are required to wash the bridge using pressurized water, with the aid of power brooms, air compressors and other hand tools,” Shaffer said. “The water pressure is required to be sufficient without the aids of detergents, so detergents are typically not used because they are not necessary.”

Different bridges, different cases for washing

In the case of the U.S. 30 bridge, the washing comes after a $1.2 million project that installed a deck overlay and replaced the bridge joints. Shaffer said some smaller bridges are washed on a bi-yearly basis and others at an even lower frequency.

“The frequency of washing is dependent upon the importance of the bridge and the severity of salt and accumulation of foreign material,” he said.

When it comes to the state’s larger crossings, like over the Mississippi or Illinois rivers, washing is a yearly or a twice-yearly affair.

“You want to make sure you maintain your more expensive assets often,” says District 2 Field Engineer Bryan Monk, whose area contains five Mississippi River crossings that IDOT maintains. “The longer that salt sits on top of the bridge, the more opportunity it has to seep down into the nuts and bolts of the bridge. You want to get it off of there, especially on any kind of steel structure. You just want to power wash it off of there, get it nice and clean, and mitigate that potential for corrosion.”

Monk also stressed that each bridge washing project carries its own set of special provisions of the work that is needed to be done.

“It might say on this bridge you’re just washing the deck surface and the parapets. On some of the bridges with steel girders, they want you to get down and wash 15 feet on each side of the expansion joint,” he said. “Basically, anywhere saltwater can get in and sit on the structure, we want to clean that up. We want to prevent the corrosion from ever happening.”