Investment in infrastructure is a hot topic these days in the United States. During his presidential campaign, candidate Trump promised to deliver a proposal for a massive infrastructure bill during his first 100 days in office, but it has not happened yet. He initially proposed a package including $137 billion in federal tax credits to private firms that back transportation projects, which Trump indicated would lead to $1 trillion in investment over 10 years. Senate Democrats are opposed to the plan and in late January announced their own “blueprint” for infrastructure spending that calls for a trillion dollars of spending on transportation, schools, “energy infrastructure,” and water and sewer systems over 10 years, but does not include tax credits for developers.
There certainly is a need for a focus on the topic. Much of the infrastructure in the United States is aging and in significant need of repair at the least and in some cases full replacement. The United States falls far behind many other nations when it comes to maintaining its key infrastructure. In fact, in 2013, the American Society of Civil Engineers gave America an overall grade of D+ based on the physical condition and needed investments for improvement. Various sectors also received individual grades based on their capacity, condition, funding, future need, operation and maintenance, public safety, resilience, and innovation. The solid waste sector received the best grade (B–), while infrastructure related to levees and inland waterways both received a D–. Fortunately, none were considered to be failing, but most rated poor with just a couple considered mediocre or good.
The wastewater sector received a D. That is not surprising considering that much of the nation’s wastewater and sewer infrastructure is 50–100 years old and must be rehabilitated to remain in use for a growing population, according to Jim Osborn, president of Osborn Contract Services Inc., a South Carolina-based certified applicator of spray-applied coatings and rehabilitation products.
The environment in municipal wastewater treatment facilities, sewers, and vaults is severely corrosive. The infrastructure is subject to continual chemical exposure and heavy abrasion that deteriorate concrete and corrode steel in clarifiers, containment pits, anaerobic digesters, manholes, tanks, and other infrastructure assets. The result: the development of sizable cracks through which wastewater can escape (exfiltration) or groundwater can enter the wastewater system (infiltration), according to Osborn. “Leaks, cracks, and damage to existing coating systems not only top the list of challenges in facility maintenance and new construction, but can also trigger severe penalties if municipalities or industrial facilities are found in violation of EPA judicial consent decrees,” he adds. The consequences can include withholding of federal tax money until the problem is fixed.
One solution that is proving effective for wastewater infrastructure rehabilitation is advanced polyurea coatings and liners. “Polyurea systems deliver strong, flexible, abrasion- and chemical-resistant waterproofing that not only bridge existing cracks, but can elongate up to 400% without cracking. Because they set and cure rapidly, and can be installed and used in a wide range of temperatures, they also minimize facility downtime,” asserts Osborne. They are an improvement over traditional cementitious materials, which can be degraded by hydrogen sulfide gas, and epoxies, which have limited elongation capabilities and thus do not effectively bridge cracks, according to Osborne. He adds that polyurethanes have more elongation than epoxies, but still fall short of the performance of polyureas.
For concrete repairs in wastewater infrastructure from municipal manholes and lift stations to clarifiers, trenches, and sumps, Osborn has transitioned to an advanced polyurea system from VersaFlex, a manufacturer of spray-applied protective coatings and waterproof membranes for the U.S. wastewater and industrial markets. The coating creates a seamless, waterproof, durable protective liner that stops leaks and strengthens the integrity of the entire structure, while also providing the elongation (up to 400%), crack bridging, hardness, and tensile strength properties necessary for the formation of a robust industrial liner that protects, strengthens, and waterproofs concrete wastewater infrastructure, according to Osborne. “Since the polyurea system provides superior elongation, it bridges cracks up to one-eighth. In addition, while tensile strength is higher than traditional materials, it has much lower permeability for better waterproofing. Its impact, abrasion, and chemical resistance are also excellent so it resists hydrogen sulfide,” he explains. As a result, unlike cementitious coatings that need to be replaced within a few years, the polyurea coating often lasts for decades.
The polyurea coating also sets and cures quickly, minimizing wastewater treatment plant or infrastructure downtime, which can translate into thousands of dollars per hour of savings as well as avoiding days of service interruption, according to Osborne. In addition, unlike conventional repair systems, the polyurea coating can be applied at temperatures ranging from -40°F to +350°F and is designed to withstand both freeze-thaw cycling and wide temperature and humidity variation. Furthermore, the polyurea coating reduces the need for continual clarifier maintenance. “Typically clarifier maintenance crews need to use high-pressure power washers for hours to clean solid waste from concrete surfaces,” says Jennifer Hoop, president of Conco Spray Solutions, an Indianapolis, IN-based contractor specializing in the rehabilitation and protection of municipal infrastructure including potable, storm, and wastewater systems. “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.”
Like many other coatings, however, it is important to note that proper crack repair and surface preparation is essential. When done correctly, the polyurea coating can be applied directly to concrete and similar substrates as a thick film. In situations where surface and/or crack repairs are not possible, pre-spraying the polyurea to geotextile fabric panels placed above the onsite substrate is a potential alternative method. The panel edges are then fused together with additional polyurea.
“For wastewater-related rehabilitation, polyurea is a superior coating for any application that requires crack bridging, longevity, chemical and temperature resistance, as well as fast turnaround,” concludes Hoop.