Grouting Helps Control Infiltration

With established standards, better products and evolving application techniques, grouting is gaining ground in municipal collections systems.
Grouting Helps Control Infiltration
Grouting crew members guide the lubricated lateral packer to a manhole in Naperville, Illinois.

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Grout is coming into its own as a remedy for collections system inflow and infiltration.

The types and specific uses for grout have never been more diverse. And with national standards for grouting now well established, municipalities and contractors have never had better guidance for when and how to grout or what materials to use.

Yet it’s still a lesser-known option for municipal I&I prevention. Methods such as cured-in-place pipe lining have gotten a lot of attention, and deservedly so. But the benefit of using grout to supplement CIPP has gotten lost in the shuffle, says Tony Conn, wastewater collections and pumping supervisor at the Department of Public Utilities for the City of Naperville, Illinois.

Naperville has seen substantial I&I reduction since it added grouting to its protocols for CIPP lining to repair mains and laterals two years ago.

“It seems like there’s not a whole lot of understanding of what lining can and cannot do,” Conn says. “You really do need to incorporate grouting in your lining program, and there’s not a whole lot of advertising” aimed at pointing that out, he adds. “Grouting companies need to start advertising lining and grouting as a combination.”

Grouting isn’t only useful as a supplement, however. “It’s becoming more and more of a stand-alone practice,” says Michael Vargo, a senior technical consultant with Prime Resins, based in Conyers, Georgia. Depending on the situation, grouting can be conducted as an independent operation or it can be used in conjunction with lining and spincast manhole repairs.

Word about grouting’s benefits may be starting to get out. “In the last five to seven years, grouting has become very, very beneficial to a lot of municipalities, saving them a lot of money,” says Pam Sawatzke, general manager for sales and marketing at Sealing Systems Inc., based in Loretto, Minnesota. That savings comes from reducing the volume of liquid flowing to the treatment plant by keeping out I&I, but also because, relatively speaking, grouting is a lot less expensive than some other approaches.

When it comes to I&I repair, grouting “is the least-cost, highest-reward technology,” says Don Rigby, vice president of marketing and education for Avanti International.

Grout in some form has been on the market since the 1950s. Initially conceived as a means for improving soil structure to support underground lines, grout began to be looked at as a possible pipe sealant starting in the 1960s.

Rigby says the first decade or so after that was a time of tentative experimentation, as engineers and sewer repair experts explored grout’s capabilities.

Experimentation flourished over the next three decades, but the results were often very uneven because the industry had no standards or regulations.

In the last 10 years, that “Wild West” culture, as Rigby calls it, has matured considerably. There has been extensive testing to determine the most effective amounts, types and application methods of grout for various purposes. That culminated in 2012 with the development of industry standards for using grout in sewer line repair, promulgated by NASSCO in cooperation with the Infiltration Control Grouting Association, an industry group.

Types of grout

Grouting by itself is best suited to combating infiltration, says Vargo of Prime Resins. “If a manhole is structurally sound and the issue is strictly infiltration, grouting is the only step needed to protect that manhole. Chemical grouts are not for structural repairs. You can’t rely on them for any structural integrity.”

There are a number of varieties of grout. The two broadest categories are cement-based and chemical grouts. Although cementitious grouts still have their uses and are by far the least expensive material, they’re rigid. If there’s any likelihood of movement or shifting in the infrastructure being grouted, they’re vulnerable to cracking and producing a new leak all over again, Vargo says.

Chemical grouts are made of polyurethane or acrylic, or occasionally other materials. Within that category are numerous subcategories. The two broadest are hydrophilic (water compatible) and hydrophobic (water averse). Hydrophilic grouts can bond to wet materials such as concrete in a manhole or at the boot seal where pipe connects to the manhole, Vargo says. Hydrophobic will not.

Hydrophobic grouts also tend to be rigid, while hydrophilic grouts are more flexible. A hydrophobic grout might be used to fill a void or pocket outside a leaking structure — in the earth surrounding the manhole, for example — as long as the area isn’t actively wet from leaking. If the leak to be repaired is actually inside the structure of the pipe, the hydrophilic grout will be more effective, Vargo says.

Thanks to their flexibility, hydrophilic grouts are also more effective where the infrastructure is subject to significant shifting. That also makes them a good companion to compression seals for repairs.

Another way to categorize grouts is based on their reaction time. Slow-reacting grouts are used to repair leaks that are relatively small and often more out of the way, explains Sawatzke of Sealing Systems Inc.

Fast-reacting grouts are for fast, heavy leaks. “If you have a 20 gpm leak, you’re going to want something that sets up rather quickly to stop that water immediately,” Sawatzke says.

Another differentiation is between single-component and dual-component grouts, she adds. The faster grouts are usually of the dual-component type, which is a focus of Sealing Systems’ product line.

Application

Grout is applied in a number of ways depending on the type and usage. A typical approach for manhole grouting requires drilling a hole through the manhole structure in order to apply grout to the outer portion of the structure, Sawatzke says. That requires care and precision to ensure that the grout applicator actually gets all the way through to the outside surface of the structure, where it will do the most good.

In other situations, crews apply grout with a portable electric pump that sprays it into place, says Vargo. In some situations, an even more basic technology will suffice, he adds — “as simple as a cartridge that fits a standard caulk gun.”

For some manhole grouting, utilities aiming to prevent hazards to their employees have started using application techniques that keep workers outside the manhole structure. “They’ve gone to grouting their manholes by doing it from the exterior,” Vargo explains. Grout can be injected around the outer perimeter of the manhole structure through probes placed in the ground from the surface.

Avanti’s grouting products for sewer line and lateral line joints are applied using machinery that resembles wheel-mounted sewer cameras, except with grout application machinery instead of cameras. The rolling grout packers are built by Aries Industries, which has been working with Avanti to develop and market the system.

The application packers are inserted into the sewer line as a camera would be, except that instead of video cables that extend back to the control truck, they are on the end of a bundle of control cables that include tubes carrying the grouting material. An Aries pan-and-tilt sewer camera is also used to monitor the process.

When the packer reaches a failed joint or other segment of the pipe needing repair, the operator stops the unit, inflates bladders at the front and rear of the packer to isolate the repair site, and then pumps grout into the opening that needs to be sealed. Rigby explains that the grout is pumped out in sufficient amounts to form a sort of collar around the outside of the pipe at the failed joint. The grout “forms a matrix with that soil that is an impermeable barrier,” he says.

Making the case

Among the strongest arguments for grout as an I&I remedy is its cost. “When it comes to leak sealing, the biggest thing is return on investment,” Vargo says.

Municipalities that use grout properly find that “for a couple thousand dollars’ worth of grout, they can save a large amount of money.”

Even if a system may need to ultimately employ other techniques such as lining, grout can effectively stop major sources of I&I and buy the utility or municipality some time until the budget allows for more expensive repairs, he adds.

Vargo and Rigby both have encountered the same misconception about grout — that it doesn’t last. “In the earliest days there were a lot of installations that weren’t done properly,” Vargo says, noting that created the impression that grouting was only temporary. In fact, grouting can be a permanent repair, “provided it’s properly installed,” he says.

Rigby sums up the common misconception in one word: “Longevity,” he says. “The belief that grouting is a temporary process.” Utility engineers view it as temporary, when it fact it can be a “long-term permanent cure.”

A 20-year study by the U.S. Department of Energy gave acrylamide grout the top rating for its ability to contain hazardous nuclear waste buried underground, Rigby says. So far, though, the material simply hasn’t been in place long enough to convince some engineers of its long-term stability and reliability. But he’s confident that will happen eventually.

“What we now have are guidelines for how to do this,” Rigby says. “You have the same results each and every time. Grout is chemistry, and it does the same thing every time.”



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