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Organic “High-Build” Spray-in-Place Liners – An Emerging Class of Rehabilitation Methods
As the water distribution infrastructure continues to deteriorate across North America, there is a continued need to develop pipeline rehabilitation methods that are cost effective and minimally disruptive, while also minimizing the time a pipe must be taken out of service.
Spray-on linings that satisfy the requirements of NSF 61 are one such emerging class of rehabilitation methods for pipes and conduits subjected to internal pressure. This article provides an overview of spray-on lining methods in general, and chemically hardened lining products in particular. The article focuses on polyurethane and polyurea, which are gaining growing acceptance in various segments of the municipal water facilities rehabilitation market in Europe and North America.
Spray-on linings currently used in waterline rehabilitation are either cement-based or polymer-based as seen in Figure 1. Each of these spray-on linings is formed by two or more substances that, when combined, result in a chemical reaction that form a hardened material shaped to mold along the pipe wall or pipe deformities. The application of lining for the rehabilitation of water pipes is century-old, with hand-applied cement-mortar lining dating back to the early 1900s. Spray-application of cement-mortar lining in larger diameter pipes started in the 1930s, and was expanded to small-diameter pipes in the late 1950s. Cement-mortar lining provides a corrosion resistant barrier between the inner wall of the pipe and its contents, increases flow and improves water quality by addressing color and odor issues. Its cost-effectiveness and ease of application made cement-mortar lining a popular means for rehabilitation of water pipes over the past 50 years.
However, hardened cement mortar does not possess significant tensile strength and therefore cannot provide the host pipe with additional internal pressure capability or compensate for lost internal pressure capacity in the case of substantial wall thickness loss, limiting its application to cases where the host pipe has maintained its overall structural integrity (Bontus et al., 2005). In an attempt to increase its tensile strength, steel fibers were added to the cement-mortar mixture with some success. Another shortcoming is the relatively long setting time and the relatively slow strength gain rate, which necessitate removal of the waterline from service for a prolonged period, requiring the installation of a temporary water supply system.