When the time to complete 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, South Carolina found when his company was working at a manufacturing plant near Charleston.
The manufacturing company produces industrial carbon products. During their process, carbon is heated in furnaces to remove impurities. Hot air (225° - 250° F) containing a high concentration of sulfur dioxide is vented from the furnaces through underground tunnels to an air scrubber system outside the plant. The twelve-year old tunnel system was constructed of fourteen-inch reinforced, cast-in-place concrete. Because the floors of the tunnels were below the normal water table, the side-walls were originally poured with a bulb type water stop at the cold joint with the floor. Sand was back filled four feet outside the walls.
The annual television inspection of the tunnels showed that they appeared to be in good shape considering the harsh environment and their age. 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 evidence of deterioration on the surface of the concrete floor. Phillips Industrial Services of Mount Pleasant, South Carolina was hired as the general contractor to repair a section of the tunnel that had significant water intrusion. Based on observations from the television inspection, Jim Miller, Project Manager, decided to pressure wash the walls and floors, patch the random cracks, and repair the floor joints to stop the water leaks. He then planned to pour a four-inch concrete overlay on the deteriorated floor, and finish the job with an epoxy/fiberglass mat coating system to be applied over all concrete surfaces. The joint and crack repair work was subcontracted to Concrete
Restorations, Inc. They were to reseal the floor joints using oakum (a dry rope-like material) saturated with Prime-Flex 900 LVSF, a hydrophilic polyurethane grout. The saturated oakum would be
pressed into any openings in the floor joints. When the Prime-Flex 900 LVSF in the oakum contacts water, it expands quickly to seal the joint. The oakum remains imbedded in the grout and increases the durability of the seal. Concrete Restorations would also inject any leaking cracks with Prime-Flex 900 LVSF.
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As each hole was drilled through the side wall, steaming hot water shot out three to four inches into the tunnel. |
With this plan in place, the plant’s first ever four-day shutdown was scheduled. Shortly after the work started, it was apparent that the problems were different from what was expected.
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 proved to be ineffective. 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. Apparently the bulb seal at the cold joint had failed.
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 were on-site from Prime Resins. They decided that the first priority would have to be stopping the leaks at the cold joint. Michael Vargo recommended injecting Prime-Flex 910 (a hydrophobic polyurethane grout) around the outside of the cold joint so it could form a watertight curtain. He recommended drilling through the wall every eighteen inches 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.
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Injecting Prime-Flex 910 aroumd the outside of the cold joint to form a watertight curtain |
At the meeting, it was also agreed to abandon the plan to install the epoxy/fiberglass mat system
because of concerns about achieving a good bond with the acidic concrete surfaces. However, the other three components of the repair (sealing the random cracks, repairing the expansion joints, and pouring the concrete overlay) would still be done.
Michael Vargo contacted Prime Resins’ manufacturing plant and made arrangements to ship a pump, Prime-Flex 910 and large supply of bang-in ports to the job-site by the next morning. Overnight, the work crews started drilling injection holes through the fourteen-inch thick concrete walls. As each hole was drilled through the side-wall, steaming hot water shot out three to four inches into the tunnel. Tests of this water showed a pH reading between six and seven indicating that it had not been contaminated by the sulfur dioxide. Samples of the Prime-Flex 910 were then injected into containers filled with the hot water to confirm that the material would cure properly.
Crews began injection at 9:00 a.m. To save time, they installed bang-in ports and then injected Prime-Flex 910 grout into each hole until material started to flow out through the adjacent hole. After about an hour and a half, it was apparent that most holes were taking a little over a half gallon of grout. At that rate, it was obvious that the work could not be completed in the necessary time with a single injection pump. At that point, Michael Vargo arranged for a second pump to be delivered to the job-site.
While the injection work was being done, another crew cleaned and repaired the expansion joints. They saturated oakum with Prime-Flex 900 LVSF and worked it into each joint and then wetted it down with a pressure bottle sprayer. They used eighty linear feet of oakum and fifteen gallons of Prime-Flex 900 LVSF to repair the joints. The grouting and expansion joint repairs were complete right on schedule at 11:00 p.m., and the tunnel floor was ready for the concrete overlay.
In just 25 hours, working in an acid-contaminated area in sauna like conditions, Concrete Restorations had drilled 342 holes through fourteen inch concrete, set 342 bang-in ports, injected 260 gallons of Prime-Flex 910, and repaired eighty linear feet of expansion joints. During that time, Prime Resins had delivered a pump and all of the necessary Prime-Flex 910 and bang-in ports.
Because Phillips Industrial Services and Concrete Restorations were able to react quickly, develop a new plan, and implement a sound repair on schedule, the facility owner contracted to repair the remainder of the tunnel system in three future phases.
