A Manhole Makeover

Kansas City rehabilitation renews manholes structurally and stops microbiologically induced corrosion

A Manhole Makeover

Inflow and infiltration are a problem for Kansas City’s 66,000 manholes, which are mostly brick and very old. The city’s contractor has been successfully rehabilitating the manholes with the Permacast system from AP/M Permaform.

The sewer system in Kansas City, Missouri, is big and old, nearly 318 square miles of combined and separate sewer networks including many still-functioning sections built pre-Civil War.

A century and a half later, the mostly clay and brick infrastructure is, understandably, failing. This is particularly true when it comes to manholes. “Kansas City has more than 66,000 manholes in its system, mostly brick, and mostly very old,” says Andy Shively, special assistant city manager. “And prior to the Smart Sewer program, there was no formal maintenance program in place to address manhole issues.”

The Smart Sewer program is a massive, 25-year, $4.5 billion public works initiative — the largest in Kansas City history — aimed at reducing the volume and frequency of sewer system overflows. Investment in sewer infrastructure is always a good idea for municipalities of all sizes, but in Kansas City it’s more than just a good idea, it’s the law — the program was formed in response to a Federal Consent Decree issued as part of Civil Action No. 410-cv-00497-GAF. The 87-page document lays out strict guidelines for “implementation of sewer system remedial measures and post-construction monitoring” including certification, inspection, funding and penalties.

Spending on inflow and infiltration reduction alone is earmarked at $250 million, and manhole rehabilitation is a big part of that. “I&I is cumulative — it gets into our system from laterals, pipelines and of course manholes,” Shively says. “And 80% of manhole I&I is from the chimney, so we want complete rehabilitation of manholes, not just new lids or joint sealing.”

Many of those manhole chimneys will be sealed and structurally rehabilitated with a spraycasting or spincasting system named Permacast, developed by AP/M Permaform. The process applies multiple, thin, smooth layers of fine aggregate composite concretes and an anti-microbial admixture, manufactured by ConShield Technologies.

“Epoxy doesn’t work well in Kansas City: It seems to fail after the freeze-thaw cycle,” Shively explains. “We have experience with centrifugally cast concrete pipe systems and spraycasted systems going back to 1993, and we’re sure that this structural, long-lasting rehabilitation will meet our I&I reduction goals here.”

Efficient process

“I think the city is doing everything they can to eliminate manhole I&I, and they’re emphasizing structural and anti-microbial rehabilitation methods with very long life cycles,” says Bryan Dobson. “That’s a great approach, and it’s going to benefit Kansas City for many decades.”

Dobson is operations manager for Ace Pipe Cleaning (Carylon), a sewer cleaning firm with national presence that’s headquartered in Kansas City. Ace Pipe Cleaning has been applying the Permacast process to the city’s manholes for about two years and in that time has rehabilitated nearly 1,500 manholes, which equals about 15,000 vertical feet of rehabbed manhole. “We shoot for 50 vertical feet per day, per crew, and will have three crews working if there’s enough work,” Dobson says. “And it looks like we have at least another 10,000 to 12,000 vertical feet coming up.”

Ace Pipe Cleaning crews can do this much work in a day because Permacast is extremely efficient. Manhole work begins after sewer pipe rehabilitation is complete, and the first step is high-pressure blasting, 4,000 to 5,000 psi, applied with a rotating tip that is lowered into the manhole and withdrawn. Once the manhole is cleaned, spraycasting — with a handgun or a bidirectional spincaster — begins immediately.

“We can apply a 1-inch-thick coating in one session, building up thin layers and spraying from multiple directions to fill in ‘shadows’ and get even, smooth coverage,” Dobson says. “Then we inspect visually, hand trowel as needed and move on.”

The materials applied are an important feature of the Permacast system. In Kansas City, Ace Pipe Cleaning is spraying MS-10,000, a fine-aggregate composite concrete that incorporates precisely graded quartz sands, nonmetallic fibers and other complex admixtures to achieve a unique blend of strength, adherence, short cure times, thixotropy (viscosity) and other desirable properties that make it an excellent choice for vertical pipe rehabilitation. “MS-10,000 covers and sticks well, and when it cures, it’s stronger than the original manhole, with very little reduction in manhole diameter” Dobson says.

Part of the Smart Sewer program is extremely rigorous inspection and quality control. After a minimum curing period of seven days, Ace Pipe Cleaning’s Permacast work is vacuum-tested to 10 inches Hg. “That’s pretty rigorous, and we’re always happy when we pass the vacuum testing,” Dobson explains. “It’s tough to restore hundred-year-old brick manholes to like-new condition, so you have to celebrate that.”

Ending corrosion

Another feature of the Kansas City work is the routine use of ConShield, a concrete admixture that prevents microbiologically-induced corrosion, which is a contributing factor to sewer failures in most Midwest cities. “The MIC damage depends on where in Kansas City we’re at, and some areas are worse than others,” Dobson says. “But applying ConShield to every manhole fix is a good idea because permanently ruling out MIC is a good idea.”

Unlike surface coatings, like epoxy, ConShield’s antimicrobial action doesn’t depend on keeping acid-producing Thiobacillus colonies away from concrete. Rather, ConShield modifies the cement matrix and makes it intrinsically hostile to microbes so that Thiobacillus colonies don’t form in the first place. As a result, they never produce concrete-destroying sulfuric acid.

“We’ve been using it for four years, and when I’ve followed up on our early projects, I’ve verified that ConShield really does eliminate corrosion — the concrete on those projects still looks new,” Dobson says.

Shively reports Kansas City is happy with the manhole rehabilitation project so far. “The quality of work is good; we’re on schedule and within budget,” he says. “And since we finally had some rain this year and have installed 150 new flowmeters, we were able to verify that we are substantially reducing I&I — enough to make a real difference. It looks like our sewer system is going to perform well for another 150 years!”


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