Chemical grout stops leaks.
Although chemical grout has been widely used for more than 40 years, many engineers and building owners are not aware of its uses, nor the time, costs, and benefits involved in typical applications. The following examples were chosen to illustrate these points.
One Saturday when the chief operating officer of Erie City Water Authority, Erie, Pennsylvania, was playing golf at a municipal course, he drove a ball into a small stream that ran across the fairway. When he bent down to retrieve the ball, he smelled chlorine and wondered why treated water would be in the stream. Since two, five-MG potable water reservoirs were buried immediately upstream, he asked that tests be made to determine if they were leaking. One tank was built in 1905 and the other in 1937. Those tests revealed that one tank was leaking about 500,000 gallons of treated water every 24 hours. The second tank was leaking much less.
Divers who visually inspected the tanks' interiors found a two-in. layer of silt on the tank bottom, but could not find any apparent leaks. This caused Ted Fithian, P.E., president, KLH Engineers, Inc., consultants to the Authority, to suspect that minor leakage was occurring through cracks and construction joints. Each tank had 3,897 linear feet of exposed, interior construction joints that had originally been filled with asphalt tar. Seepage through all the joints would allow 500,000 gallons to leak out daily without creating enough velocity to disturb the silt.
KLH considered various repair methods, including liners and a new concrete slab, but decided that chemical grout would be the best solution. Since the tanks were structurally sound, it was only necessary to stop water from seeping through joints and cracks in the concrete. Chemical grout could seal hairline cracks or large voids equally well.
The engineers specified a hydrophilic (water-activated) polyurethane system. 3M's Scotch-Seal 5600 Chemical Grout was selected for several reasons. Because it has low viscosity (300 to 600 cps) until it comes into contact with water, it can be pumped into hairline cracks with relatively low pressures (700 to 800 psi). Another reason is that grout, when activated by water, foams to between 8 and 10 times its original volume and forms a mechanical lock, as well as a compressive and adhesive bond with the crack surfaces. In its cured state, the grout is a rubber-like material that is impermeable to water, and NSF approved for use in potable water.
After a tank had been drained and cleaned, the asphalt tar used to seal the original construction joints was removed with high-impact pressure washers. Foam rods that were twice the width of the joints were then dampened with water, saturated with grout, and compressed into the construction joints. After the grout swelled and cured, a grout needle was used to inject additional grout through the foam to seal any space underneath, and to improve the adhesive, compressive, and mechanical bond. Cracks in the floor and walls were sealed through a series of holes fitted with injector packers.
Each tank was taken out of service about 90 days for the rehabilitation work. Frank Burns, president, State Pipe Services, Inc., Cranberry Township, Pennsylvania, the contractor who performed the work, said the job was bid sight-unseen because the tanks were in service. "The first time I went into one of the tanks, I wondered what I had gotten us into. Each tank is about the size of a football field and 25 feet deep," he said.
After the repairs were complete, tests showed that 96 percent of the leakage had been stopped in one tank and 98 percent in the other. "Stopping the loss of that much treated water will pay for the entire repair in a year," Burns said. "I knew we could stop the leaks. We've used chemical grout to stop thousands of leaks, and I have never had a call-back on a single one."
When leaks were discovered during a routine inspection of Soda Dam near Soda Springs, Idaho, the owners ordered tests to determine the condition of the dam. The tests found that the dam was structurally sound, but that continued seepage of water through the cracks and joints could weaken it, leading to more leakage and perhaps, eventually, to a sliding failure. The decision was made to stop the leaks.
Remedial techniques considered and their respective costs included:
* Removing and replacing the concrete over the upstream face of the dam - $472,000;
* Covering the upstream face with a two-component membrane (PVC and geotextile lining) - $605,000;
* Sealing all construction joints and cracks with chemical grout - $156,000 to $277,000.
Chemical grout was chosen as a cost-effective and efficient technical alternative.
While the water in the reservoir was lowered 45 ft to permit the replacement of spillway piers, the joints and cracks on the upstream face were identified and mapped. About 800 ft of cracks and joints were identified as requiring treatment.
AV-220 Hydracure, a one-component chemical grout from Avanti International, Houston, Texas, was chosen for the repair. This polyurethane resin system reacts when it comes into contact with water and forms a flexible, dense foam, which adheres to the surfaces of cracks and joints. The result is a tough, tight-fitting, highly resilient, rubbery seal that is immediately impermeable to water.
A staggered pattern of holes was drilled to intersect the cracks and joints at least 10 in. from the upstream face of the dam. After a six-in. long mechanical packer was placed in each hole, water was injected for five minutes to test the tightness of the crack, ensure grout activation, and achieve maximum penetration of the grout.
A total of 290 gallons of grout was injected into 450 holes at an average pressure of 1,700 psi. Grout acceptance varied from zero to five gallons per hole, with only one percent of the holes accepting none. The final cost of the entire chemical grout program was $196,000.
Since the completion of the project, no measurable leakage through the dam has been found.
The New York Subway System has a lot of problems with water leaks. Leaks into the subway system create significant safety liabilities such as the danger of electrical shock or slipping in water puddles, but leaks can also degrade the structural integrity of the tunnels.
Fifteen years ago, Tom Planert, P.E., President, SSESCO, Inc., Fairfield, New Jersey, introduced the subway engineers to the idea of using urethane-based chemical grout to stop leaks. They asked him to make a repair for their evaluation.
That first job was at Bergen Street Station, the lowest point in the subway system. It took almost six months to get both sides of the station platform area dry, but the agency was impressed with the low cost and the result. Then, they waited a year to see if the grout would hold. After all, they had used a lot of materials in the past which had held for a while, but had blown out after the first ground movement.
"That station is still dry," Planert said." And since then, we've successfully sealed miles of cracks for the subway. I don't know of any other materials that can stop leaks in existing cracked concrete as permanently as chemical grouts," he added.
In the final analysis, of course, success with chemical grout depends on the applicator, so guarantees are only as good as the company that makes them. A wide range of chemical grout products is available, but only experience can produce the in-depth knowledge of when, where, and how to use them.
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|Date:||Jul 1, 1998|
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