Photo Courtesy C.A. Rasmussen Inc.
Repair crews blast fire-damaged concrete from tunnel sections, which are treated with shotcrete and epoxy. They skip the adjacent section to facilitate curing, then return to repeat the process.

Working on a tight, two-month time schedule, contractor C.A. Rasmussen, Valencia, Calif., is completing work on a major Interstate 5 connector tunnel near Los Angeles that was severely damaged last July 13, when a tanker truck carrying 8,500 gallons of fuel overturned and burst into flames.

"We're working double shifts night and day, every day, trying to get this fast-track project done on time," says Adam Rasmussen, project manager.

Rasmussen, whose company won a $16.5-million contract on Nov. 5, is scheduled to turn the freeway section over to Caltrans on Jan. 8, when it will reopen to about 300,000 average daily motorists. Caltrans needed the work fast-tracked because the Federal Highway Administration gives a state 180 days after an initial emergency to earn 100% reimbursement.

To finish on time and avoid a $3,000 daily late fee, the company hired three subcontractors and put up to 60 workers per day on the job. Project completion means replacement of 70% of the 400-ft-long tunnel, or about 35,000 sq ft of concrete on the walls and roof and roughly 800 ft of roadway within the tunnel. The contractor also will reinforce outrigger beams and support columns.

Caltrans structure representative James Shih says the extreme fire didn't melt the concrete, but it did cause the concrete to spall and delaminate up to 4 in. below the surface. To remove the damaged material, Rasmussen sub-contractor Hydro Pressure Corp. will use a hydro-demolition or hydro-blasting machine that uses a robot arm to shoot a jet stream of water at 20,000 psi.

"Hydro demolition provides faster removal times and does not damage the existing reinforcing steel," says Shih, who is with Caltrans' Office of Structure Construction. "This technique is not unique. However, it is not generally used in traditional bridge demolition projects since most do not typically remove only surface concrete at such a large scale."

Rasmussen says crews are blasting off the concrete in 70-ft by 20-ft sections in a "hopscotch" pattern. He says they remove a section, fill it with shotcrete and epoxy where needed, then skip a section while the new concrete section cures.

"The most difficult part of this project has been coordinating all the trades working in a small, confined tunnel at once and on top of each other, without compromising safety or quality," says Rasmussen, whose family business has been around for three generations. "This is not how a normal project is built."

The fire occurred when the truck hit a column and flipped inside a tunnel underpass, where I-5 meets the state Route 2 (Glendale) Freeway, a couple of miles north of downtown Los Angeles. With the tunnel still smoldering, Rasmussen was hired by Caltrans on an emergency $5-million contract and arrived on the scene within six hours of the crash.

Over the next 72 hours, the company worked continuously to break off and haul away compromised concrete and, with a falsework structure, stabilize the burned and spalling tunnel ceiling. Designed by Parsons Bridge Design Group, the support system was engineered to carry the highway's daily load. Caltrans says that, under normal circumstances, the process would have taken months for a contractor to complete.

After the initial repair in July, Caltrans closed the tunnel and rerouted traffic locally, while engineers devised a permanent fix. In August, the materials engineering and testing services department began concrete strength tests. Engineers used ferro-scanners and drilled holes to insert cameras to assess damage.

Besides replacing burned concrete, Rasmussen also is placing carbon-fiber wrapping around affected outrigger beams on the north side of the connector, repaving the roadway, upgrading metal- beam guardrails, installing 500 new lights and adding anti-graffiti coated paint.