Industrial tunnel repair yields dangerous curve ball
General contractor: Phillips Industrial Services, Mount Pleasant, S.C.
Subcontractor: Concrete Restorations, Charleston, S.C.
Client: A Charleston, S.C., industrial carbon products manufacturing plant
PROBLEM: When the timeline for a repair project is tight and you encounter an unexpected expansion in the scope of work, you have to be able to react fast. That’s what Don Ford of Concrete Restorations of Charleston, S.C., found when doing work at a manufacturing plant near the city that produces industrial carbon products in the late 1990s. Hot air containing a high concentration of sulfur dioxide is vented from the furnaces through underground tunnels to an exterior air scrubber system. The 12-year-old tunnel system was constructed of 14-inch reinforced, cast-in-place concrete.
The annual television inspection of the tunnels showed they appeared to be in good shape considering their age and the harsh environment. However, a few random cracks were found in the walls, and some floor joints appeared to be failing, allowing water to seep in and collect on the floor. There was also some deterioration on the surface of the concrete floor.
Phillips Industrial Services of Mt. Pleasant, S.C., was hired as the general contractor to repair a section of the tunnel that had significant water infiltration. The joint and crack repair work was subcontracted to Concrete Restorations, Inc. The first ever four-day plant shutdown was scheduled.
The standing water in the tunnel was tested and found to have absorbed sulfur dioxide from the vented air, which formed sulfuric acid. Tests of the floor and portions of the walls also indicated that acid contamination extended as deep as one inch into the concrete. Repeated attempts to remove the contamination by pressure washing didn’t work. Visual examination also revealed that most of the leaking water was not coming from the cracks and floor joints, but instead through the cold joint between the floor and walls.
SOLUTION: With this new information, it was obvious that the whole repair strategy would have to change. The owner’s project engineer met with Don Ford from Concrete Restorations, Jim Miller from Phillips Industrial and Michael Vargo, on-site technical consultant from Prime Resins. They decided that the first priority was stopping the leaks at the cold joint. Vargo recommended injecting Prime Flex 910, a hydrophobic polyurethane-based chemical grout, around the outside of the cold joint so it could form a watertight curtain. He recommended drilling through the wall every 18” near the cold joint and then injecting the grout through the drilled holes. This would allow the grout to migrate through the surrounding sand and create a seal around the lower portion of the wall to the bottom of the floor slab. Vargo arranged for the necessary equipment and supplies to be overnighted from Prime Resins.
Overnight, the work crews started drilling injection holes through the 14”-thick concrete walls. Steaming hot water shot three to four inches from each hole, but the water was not contaminated by sulfur dioxide. Samples of Prime Flex 910 were then injected into containers filled with the hot water to confirm the material would cure properly, which it did.
Grout injection began at 9 a.m. the next morning. In less than two hours it was clear that all the work couldn’t be done during the shutdown with a single injection pump at the rate they were going, so Vargo had a second pump delivered.
While this work was underway, a second crew repaired the expansion joints using the activated oakum technique with Prime Flex 900 LVSF (current equivalent is 900 XLV) and using a pressure bottle sprayer to activate the resin. They used 80 linear feet of oakum and 15 gallons of resin. Both the grouting and expansion joint repair were done on schedule.
In 25 hours, working in an acid-contaminated area in sauna-like conditions, Concrete Restorations drilled 342 holes, set 342 bang-in ports, injected 260 gallons of Prime Flex 910 and repaired 80 linear feet of expansion joints. This was done with supplies and equipment delivered from Prime Resins.
BENEFIT: The necessary repairs were completed during the shut down. Because Phillips Industrial Services and Concrete Restorations were able to react quickly and do the repair on schedule, the facility owner contracted to repair the remainder of the tunnel system in three future phases.