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Features

Rehabbing Aging Concrete Wastewater Infrastructure Using Polyurea Coatings

Posted on December 16, 2016
Written by Del Williams

As much of the Canada’s wastewater and sewer infrastructure approaches the 50-year to 100-year mark, it must be rehabilitated to remain in use for a growing population. Yet municipal wastewater treatment facilities, sewers, water mains, and vaults endure some of the most severe and corrosive environments in the infrastructure landscape.

Industrial water users face similar challenges. Many industrial water treatment facilities operate under continual chemical exposure and heavy abrasion—factors that deteriorate concrete and corrode steel in clarifiers, containment pits, anaerobic digesters, manholes, tanks, and other infrastructure assets. Over time, these structures can develop sizable cracks through which wastewater can escape or infiltration of groundwater.

In many cases, advanced polyurea coatings and liners are providing a practical option for infrastructure rehabilitation. Polyurea products deliver strong, flexible, abrasion, and chemical-resistant waterproofing that bridges existing cracks, and can elongate the lifespan of infrastructure by up to 400 per cent without cracking. Because coatings and liners are designed to set and cure rapidly, and can be installed and used in a wide range of temperatures, they also minimize facility downtime.

Moving and shaking
Cracks can develop in aging concrete wastewater infrastructure for a number of reasons, ranging from earth movement to daily or seasonal temperature changes that cause expansion and contraction including freeze-thaw. Additionally, harsh chemicals used to treat wastewater can deteriorate the concrete, as can exposure to hydrogen sulfide gas, a form of sulfuric acid present in sewers created by anaerobic organisms.

Concrete cracks or leaks that lead to wastewater exfiltration or groundwater infiltration can put the municipality in violation of regulations, triggering significant penalties and putting human health at risk. Jim Osborn, the president of Osborn Contract Services Inc., a South Carolina-based certified applicator of spray applied coatings and rehabilitation products, said that cementitious material is traditionally used to repair wastewater-related sewer leaks, but this has disadvantages.

“Hydrogen sulfide gas eats away at the cement in sewer concrete, so it may only have a lifespan of a few years,” said Osborn. “Because epoxies are limited by much lower elongation properties, they crack and don’t bridge cracks well. Polyurethanes have more elongation, but nothing like polyureas.”

Extreme conditions
Polyurea also has the advantage of being designed for installation and use in extreme temperatures, from -40°C to 100°C. “When you’re above ground in Canada, you have freeze and thaw with concrete expansion, contraction, and cracking,” said Jennifer Hoop, president of Conco Spray Solutions, an Indianapolis, Ind.-based contractor specializing in the rehabilitation and protection of municipal infrastructure including potable, storm, and wastewater systems. “We needed a lining that would move with the structure through the different seasons and tank temperature differentials. For that, polyurea works very well.”

Hoop used the polyurea for a secondary containment area around ferric chloride tanks to withstand extreme weather conditions at a northern Indiana wastewater treatment plant. “After filling in cracks with grout and restoring the concrete, we sprayed the polyurea on geotextile to provide a really nice containment area for the ferric chloride tanks,” she says.

She added, “Typically clarifier maintenance crews need to use high-pressure power washers for hours to clean solid waste from concrete surfaces. Since the polyurea provides waterproofing and has a cleanable surface, crews can simply hose down the clarifier to clean it. This can cut required weekly clarifier cleaning by two-thirds.”

Need more information? In 2010, the Water Research Foundation completed a Global Review of Spray-On Structural Lining Technologies in partnership with the U.S. Environmental Protection Agency. That study can be viewed online here.

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