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When an engineer specifies a concrete protective liner (CPL), they do so as a way to help guard concrete structures against water infiltration and corrosion. Because CPL is installed during the concrete pour, specifying CPL often necessitates fabrication—the use of tailor-like skills to cut the sheets of CPL into the specific shapes required to fit the precast concrete forms.
For the most part, all lined precast structures used in municipal sewers and landfills require some level of fabrication. While some precasters will perform the task themselves, most utilize a fabricator and especially under certain conditions. For example, fabricators are especially important when shaping CPL to fit cone forms as the shape accounts for many dimensions and will typically vary between projects. The same applies for cast-in-place projects.
In this article, we summarize CPL and its usage in modern applications, describe fabricators and the role they take in preparing concrete protective liners, and explore the various ways fabricators add value to projects utilizing CPL.
Why is concrete protection vital in modern constructions?
When water comes into contact with concrete, it has the ability to permeate and reach the underlying steel reinforcement. The water reacts with the steel to create iron oxide byproducts that build up and can create mechanical stress that leads to cracking. In regions with significant temperature gradients, the water can form into ice within those cracks and compound the structural damage. In other applications, concrete structures can experience damage due to corrosive substances in the media being contained. Industrial applications may require containment of acids or salts or other chemicals which are corrosive to concrete. Municipal wastewater systems are often susceptible to corrosive processes such as microbial induced corrosion whereby hydrogen sulfide gas generated by decomposition is converted to sulfuric acid.
Concrete protective liners (CPL) are made with thermoplastics, making them both hydrophobic and chemically resistant. In contrast with a spray-on protective coating, CPL has a robust anchoring system and can be more firmly attached to the concrete. A strong attachment in concrete provides CPL with improved resistance to groundwater/hydraulic backpressure. Because CPL won’t easily be lifted up or peeled away, lining a concrete tank with CPL provides for a more long-term and cost-effective solution when compared with alternatives.
What role do fabricators play in preparing CPL?
Fabricators are responsible for preparing CPL prior to installation. Wayne Turner, owner of Turner Lining Company, fabricates CPL for precast concrete companies that typically place the liner on forms and pour the concrete around it. Sometimes, they do a bit more.
“When fabricating for a contractor on a cast-in-place structure, we sometimes handle the installation on the form,” says Mr. Turner. In other situations, they utilize a subcontractor to perform this duty. “From time to time I will train contractors so that they can perform the installation of the liner and perform the field welding.” Proper training is important as each job is uniquely different, requiring specific solutions and welding techniques.
Ultimately, the end user is interested in a proper CPL installation, which means that the liner is properly fitted to the forms and concrete to attain good consolidation around the embedment anchors. To ensure a leak-free concrete structure, the CPL segments should be joined together by welders—specifically those who have been certified as trained by the liner’s manufacturer.
How do fabricators add value to projects using CPL?
While many projects benefit from the use of CPL, not all of these projects require a fabricator. The difficulty of the project, which is determined by the complexity of the structure to be lined, determines the level of fabrication skill required. Some projects can be performed by the installer after some training; others need experienced fabricators to perform the liner installation. When in doubt, the owner and installer can discuss project specifics with the liner’s manufacturer, who can help determine the level of control required by the project.
Often, the manufacturer will consult with a fabricator like Mr. Turner, who offers a second opinion on planning and best practices for the project. A fabricator can also help inform the end user about the importance of each phase of the project that will use CPL. The information includes details about the CPL products, dimensions, and accessories available on the market, the benefits that each product would bring to the project, how skilled fabrication can improve installation quality and times, and how to effectively implement QA. Installation feedback is especially important.
Fabricators can help recognize problem areas and alleviate installation difficulties before they occur. “Understanding and identifying locations that are hard to field weld is part of the job,” says Mr. Turner. “As is determining how to best fabricate a solution that could be shop welded and field cast to eliminate those problems.”
Fabricators help guide installations in other ways, too. They help determine concrete cast heights and joint locations, which can minimize joint welding time. They also help identify welds that can be made before casting (such as on overhead tops), saving both installation time and effort.