Polyurea Coatings For Manhole Reclamation and Sewer Infrastructure
With much of the U.S. wastewater and sewer infrastructure reaching 50 to 100 years of age, experts agree that the infrastructure must be rehabilitated to stay in use for a growing population. Yet municipal wastewater treatment facilities and sewers whether some of the water industry’s most severe and corrosive conditions. In recent years, these facilities also have been forced to pass increasing scrutiny from the Environmental Protection Agency (EPA) (Washington, DC).
In industrial facilities with a lot of waste, the EPA enforces regulations to ensure that they do not add pollutants to their wastes to protect the local sanitary sewers and wastewater treatment facilities. The extreme environments for wastewater handling are subject to constant chemical exposure and heavy abrasion, which deteriorates concrete and causes steel corrosion in clarifiers containment pits, digesters that are anaerobic manholes, and tanks along with other facilities of the infrastructure.
Concrete Cracking and Deterioration
Various factors can cause these structures to develop sizable cracks, through which wastewater can escape by exfiltration. Cracks can develop in aging concrete wastewater infrastructure for many reasons, including earth movements or daily and seasonal temperature changes that cause expansion and contraction, such as freeze-thaw. Additionally, harsh chemicals used to treat wastewater can deteriorate the concrete, as can exposure to hydrogen sulfide (H2S) gas, a form of sulfuric acid (H2SO4) in sewers created by anaerobic organisms. Groundwater could also enter the wastewater system through infiltration. Leaks, cracks, and damage to existing coating systems top the list of challenges in facility maintenance and new construction and can also trigger severe financial penalties. Since the EPA regulates municipal wastewater and stormwater management, concrete cracks or leaks that lead to wastewater exfiltration or groundwater infiltration can put the municipality in violation of a judicial consent decree.
If the EPA finds that a municipality has old leaking sewer systems, putting them on a consent decree can mean that they don’t receive federal tax money until the problem is fixed.
A cement material is traditionally used to repair wastewater-related sewer leaks. But this process has disadvantages, as do other coating materials. ArmorThane offers an advanced polyurea system for concrete repairs in wastewater infrastructure, from municipal manholes and lift stations to clarifiers, trenches, and sumps.
Hydrogen sulfide [H2S] gas eats away at the cement in sewer concrete, so it may only have a lifespan of a few years. Because much lower elongation properties limit epoxies, they crack and don’t bridge cracks well. Polyurethanes have more elongation, but nothing like polyureas.
Advanced polyurea coatings and liners are ideal for wastewater infrastructure rehabilitation by delivering strong, flexible, abrasion- and chemical-resistant waterproofing that not only bridges existing cracks but can elongate up to 400% without cracking. The spray-applied waterproof coating creates a seamless, waterproof, durable protective liner that stops leaks and strengthens the integrity of the entire structure. It exhibits superior physical properties such as elongation up to 400%, cracks bridging, hardness, and tensile strength to create a robust industrial liner that protects, strengthens, and waterproofs the infrastructure. Because these systems set and cure rapidly and can be installed and used in many temperatures, they also minimize downtime.
Characteristics of Polyurea
Several of the polyurea’s characteristics help to extend wastewater infrastructure longevity and prevent wastewater exfiltration and groundwater infiltration.
Since the polyurea system provides superior elongation, it bridges cracks up to 0.125 in [3.18 mm]. With tensile strength higher than traditional materials, it has much lower permeability for better waterproofing. Its impact, abrasion, and chemical resistance are excellent, so it resists hydrogen sulfide. Instead of years between replacing cementitious coatings, the polyurea coating can cost-effectively provide decades of protection.
With proper crack repair and surface preparation, the polyurea coating can be a thick film applied directly to the concrete or similar substrate. An alternate application method that can sometimes mitigate the need for surface or crack repairs is to pre-spray the polyurea to geotextile fabric panels placed on top of the substrate and fuse the panel edges with more polyurea.
The polyurea coating can be applied directly to the concrete with proper crack repair and surface preparation.
Because of the polyurea’s ability to set and cure quickly, it also minimizes wastewater treatment plant or infrastructure downtime. This can translate into thousands of dollars of savings per hour while avoiding service interruption days.
In one recent case, when extensive cracks were found in a concrete clarifier shortly before a chemical plant’s ribbon-cutting ceremony, Osborn turned to polyurea for superior protection and fast installation.
After repairing all cracks over 0.125-in wide in the clarifier with a concrete repair grout, this applicator prepared and primed the floor and walls with the manufacturer’s primer. He then applied 80 to 100 mils (2,032 to 2,540 µm) of polyurea.
Wider Temperature Range
While traditional coatings such as cementitious, epoxies, and polyurethanes will prematurely fail if not installed under a relatively narrow range of temperatures, the ArmorLiner polyurea used by most applicators is designed for installation and use from -40 to 350 °F (-40 to 176.7 °C). It will withstand decades of freeze-thaw cycling and wide temperature and humidity variations.
When you’re aboveground in the Midwest, you have freeze and thaw with concrete expansion, contraction, and cracking. A lining that will move with the structure through the different seasons and tank temperature differentials is necessary. For that, polyurea works very well.
This applicator selected 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, they sprayed the polyurea on geotextile to provide a nice containment area for the ferric chloride tanks. Polyurea has an added benefit in reducing continual clarifier maintenance.
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 a clean surface, crews can hose down the clarifier to clean it. This can cut the required weekly clarifier cleaning by two-thirds.
For wastewater-related rehabilitation, polyurea is a superior coating for any application that requires crack bridging, longevity, chemical, and temperature resistance, as well as a fast turnaround.