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34 CHAPTER FIVE PIPE PROTECTION, REPAIR, REHABILITATION, AND REPLACEMENT This chapter summarizes the most common available pro- tection methods and materials, and also discusses reha- bilitation, repair, and replacement techniques available to extend or reestablish culvert service life. Many agencies are developing more advanced pipe system inventories and asset management systems to facilitate better drainage infrastruc- ture management and budgeting. For example, New Jersey DOT is researching how to develop a comprehensive plan for inspection, cleaning, condition assessment, and predic- tion of remaining service life of corrugated steel culvert pipe (Meegoda and Juliano 2009). This process will aid rehabili- tation-related decision making about (1) cleaning and paint- ing, (2) invert paving, (3) sliplining, (4) in situ cured liners, and (5) pipe replacement. COATINGS, LININGS, AND PAVING Invert Paving (Concrete) Primarily used with metal culverts (ASTM A 849) to act as sacrificial material for abrasion resistance, concrete can be placed in the invert area of the pipe to a thickness of between 3 and 6 in. The thickness and width of coverage varies based on typical flow depth and anticipated abrasive potential. Although the concrete may be placed directly against clean pipe material, steel reinforcing bars, wire fabric, Nelson Studs, or a combination of the three are often welded to the metal pipe before concrete placement (Figure 27). Although concrete paving is used to rehabilitate cor- roded and severely deteriorated inverts in corrugated metal pipes, it can also be used in concrete culverts if modifica- tions are made (Figure 28). The method consists of pour- ing a concrete lining in the culvert invert, which increases surface roughness inside the pipe (and so increases Man- ningâs n value) and thus decreases flow velocity. California DOT (Caltrans 2013) use concrete invert paving ranging from 2 in. to 13 in. thick depending on the abrasiveness of the site, up to Abrasion Level 5, to achieve a 50-year maintenance-free service life. Concrete invert paving is not recommended for Abrasion Level 6. The invert pav- ing sections typically vary from 90 to 180 degrees for the internal angle depending on the extent of the deterioration on both sides of the pipe. Although concrete invert paving is generally regarded as a temporary repair, a survey undertaken by Minnesota DOT identified a case study where invert paving had lasted longer than 25 years (Minnesota DOT 2012). Ohio DOT assumes a 20-year add-on service life for concrete paving. The key performance factors are the use of high-strength concrete with durable aggregate and ensuring that the concrete insert is adequately anchored to the host pipe. FIGURE 27 Shear connector welding studs (Nelson Studs) and wire fabric being installed prior to concrete invert paving (Caltrans 2013).
35 In California, an alternative to concrete invert paving is the use of steel armor plating 0.25 to 0.50 in. thick over the bottom third of the pipe. It is mainly suitable only for large- diameter (> 48 in. diameter) corrugated metal pipe in highly abrasive water flows because of the high cost. FIGURE 28 Standard detail for concrete invert paving (Caltrans 2013). Epoxy Coatings for Concrete A wide range of proprietary epoxy coating treatments can be applied to protect and extend the life of concrete culverts. These coatings, which are usually sprayed on, are suitable for treating minor deterioration in exposed concrete sur- faces, such as popouts, minor scaling, and hairline cracks. Epoxy coatings are not appropriate for severely deterio- rated concrete or where reinforcing steel is exposed. These coatings can also be effective in protecting concrete from degradation caused by exposure to mildly aggressive flow waters. Epoxy coatings are hard and bond well to concrete if it is properly cleaned and prepared prior to application. These types of coatings should be regarded as maintenance treatments but can help to slow some forms of progressive concrete degradation and can provide add-on service life in appropriate applications. REHABILITATION AND REPAIR PRACTICES Pipe rehabilitation and repair technologies are discussed in detail in the literature review of NCHRP 14-19 (2010). NCHRP 14-19 should be consulted for additional detail on these topics. Lining an Existing Pipe Sliplining Sliplining is a method of rehabilitation in which a new pipe of smaller diameter is inserted directly into the dete- riorated culvert. The annular space between the host pipe and the newly installed pipe is grouted with a cementi- tious material. There are two primary methods of sliplining: segmental sliplining and continuous sliplining. For segmental sliplin- ing, short pipe segments are assembled as a liner at the entry of an existing pipe, and new segments are added as the liner is fed into the pipe. For continuous sliplining, a liner is man- ufactured as a continuous pipe or assembled in the field prior to insertion, to match the entire length of the existing pipe. The main advantages of sliplining are simple installa- tion, the ability to rehabilitate a wide range of pipe sizes and shapes, the ability to accommodate large radius bends, the variety of available sliplining pipes, and a reduced need for flow bypassing (Figure 29). Sliplining is often an economi- cal rehabilitation option for culverts. The method does not involve chemical processes and is environmentally safe rela- tive to other procedures. FIGURE 29 Sliplining 20-year-old corrugated steel pipe culverts with profile wall HDPE pipe. The annular space is filled with cellular foamed grout with specified strength of 210 psi (Doherty and Angelo 2012). The main limitations of sliplining are the need for pit excavation (although the digging of access pits may be avoided with shorter culvert lengths), and the grouting of the annular space (which is generally required). Other limi- tations are flow reductions in cross-sectional areas (although the smooth interior surface of slipliner pipe could restore or even increase flow capacity), the potential for increased in- pipe and downstream flow velocities, and the need for suf- ficient work area. Properly sliplined culverts should provide the full service life anticipated from the type of pipe used in the sliplining. Thus, it is generally equivalent to full pipe replacement in terms of future service life. Spirally Wound Liner Spirally wound liners are fabricated in the field from a con- tinuous thermoplastic strip that has one male and one female edge (Figure 30). During the helical winding process, the
36 male and female edges self-interlock to form a leak-tight joint. Typically, spirally wound liners use nonstructural grout or do not require grouting of the annular space. FIGURE 30 Expandable-diameter or spirally wound pipe liner being installed (Caltrans 2013). The main advantages of spirally wound liners are that they remove the need for excavation, on-site pipe storage, and bypass flow (for most applications). Installation is rela- tively quick, and the liners can accommodate large radius bends as well as diameter changes. The use of spirally wound liners does not involve chemical processes and is more likely to be environmentally safe when compared with liners that require grouts and sealants. The main limitations of spiral winding are the reduction in flow area (although the smooth interior surface of the liner pipe often restores or even increases flow capacity), and that the ends of the relined pipe require watertight sealing. The method is also only applicable to circular pipes. Caltrans (2013) use spirally wound liners for both flexible and rigid pipes to provide a corrosion barrier suitable to meet a 50-year design service life for abrasion levels 1 through 3. Spirally wound liners are not recommended for use in high- abrasion applications. Sprayed-on Liner (Cementitious/shotcrete) Shotcreting has been used as a lining for pipes since the 1990s. Shotcreting is generally a wet-mix process that uses plain con- crete mixes or mixes with synthetic or steel fiber reinforcement. The shotcrete is applied by way of a robotic rig and has been used for pipes of 24-in. diameter and wider. More recently, improved technology called centrifugal sprayed concrete (CSC) has been developed. CSC delivers the new concrete lining by way of a rotating spinner head. Projects have been completed for Colorado and Kansas DOTs. CSC produces a uniform 2-in.-thick concrete liner that achieves a compressive strength of 6,000 psi in 7 days. It has been used extensively for rehabilitating corrugated steel pipe culverts (Figure 31). If properly installed, shotcrete and CSC liners with dura- ble and high-strength concrete mixes enhance the struc- tural capacity of the pipe and provide serviceable lives that exceed 50 years. Sprayed-on Liner (Epoxy) Spray-on epoxy is used mostly for rehabilitation of potable water pipes, although it can also be used to line culverts. It generally applied with manual spraying. Epoxy can be applied as a protective coating against corrosion and to elim- inate infiltration and exfiltration. Epoxy coatings are typi- cally 100% solids and solvent-free (i.e., they do not require a solvent to keep the binder and filler parts in a liquid-sus- pension form). Application thickness is between 0.06 in. and 0.25 in. per application layer and a minimum of two layers is recommended. The main advantage of polymer-based coatings and liners is the ability to provide protection against corrosion. Some FIGURE 31 Examples of completed CSC liners (Source: Shotcrete Technologies Inc.).
37 also provide structural enhancement and no excavation is required. The main limitation is that the culvert must be completely free of water and flow bypass may be required. An extensive surface preparation is essential for successful application with some systems. Epoxy lining systems are relatively new and no data are available on life expectancy. Cured-in-Place Pipe Cured-in-place (CIP) relining is a method in which a flex- ible material (typically a tube) saturated with thermosetting resin is inserted into the deteriorated culvert by inversion or winching, expanded by means of air or water pressure, and then the resin is cured at ambient or elevated temperature (by means of steam or hot water) or with UV light. The final product, which is often referred to as cured-in-place pipe (CIPP), has minimal or no annular space, thus eliminating the need for grouting. Typical CIPP liners range in thickness from 0.25 in. to 0.5 in. The CIP liners can be categorized into conventional CIPP and composite CIPP. Composite CIP liners are high-strength, fiber-reinforced CIP liners (fiber reinforcement provides increased stiffness and strength resulting in thinner liner walls compared with conventional CIP liners) and are used to rehabilitate medium to large sewers, drains, and culverts. The main advantages of CIP relining are elimination of the need for excavation and grouting, and installation of con- tinuous single-piece (jointless) products that provide struc- tural renewal with an expected 50-year service life. CIPP is a proven technology (it has been in use for 30 years), is often cost-effective, and causes minimal traffic disruption. Small- diameter installations can be completed in as little as 1 day. The main limitations of this method are that flow bypass is needed (unless the culvert pipe is empty at the time of rehabilitation), custom-made tube is required for each instal- lation, trained personnel are required, prolonged liner cure is needed for large diameters, it can cause thermal pollution (if hot water was used to accelerate resin cure), and it can damage the environment (if styrene-based resins are used). Winnipeg, Canada, was one of the early adopters of CIPP technology in North America when it began relining its sewer pipes in 1978. Video inspection and sampling of the CIPP liners after 34 years of service has confirmed that the linersâ condition are still excellent with no evidence of mate- rial degradation or induced stress on the liners (Macey and Zurek 2012) (Figure 33). Pipe Replacement A number of trenchless technologies for pipe replacement exist, including jack and bore, tunneling, and horizontal directional drilling. These methods are not discussed in this section, but the pipe bursting/splitting method is discussed because it reuses the same alignment of the existing culvert. Pipe Bursting/Pipe Splitting Pipe bursting is a construction method of trenchless pipe replacement in which deteriorated culvert pipes are replaced with new pipes of the same or somewhat larger diameter. The bursting tool is passed through the pipe, breaking it into fragments if the pipe is brittle or slicing through it if the pipe is ductile (also known as pipe splitting), and the new pipe is simultaneously pulled in (Figure 34). The typical replacement pipe installed by pipe bursting is an HDPE pipe. Since these pipes are chemically inert, they can readily flex to meet changes in loading along the culvert length while maintaining their circular shape. Other pipe types installed using pipe bursting include fusible PVC pipe, retrained joint PVC pipe, ductile iron pipe, and vitri- fied clay pipe. FIGURE 32 Cured-in-place pipe liner being installed and after installation in a 20-year-old corrugated steel pipe; 75-year service life assumed in design (Doherty and Angelo 2012).
38 The main advantages of pipe bursting include the instal- lation of a new pipe, ability for pipe upsizing, and reduc- tion of necessary excavation by 85% or more compared with open cut replacement. It is often more cost-effective than open trenching in urban environments. The main limitations of this method are inapplicability for already collapsed pipes or difficulties that arise when exist- ing pipe composed of brittle material has had point repairs with ductile material. Pipe bursting can cause ground heave or settlement above or at some distance from the culvert, especially in dense sand, when the culvert pipe is shallow and ground displacements are primarily directed upward, and when significant diameter upsizing is performed. In addition, pipe bursting is not applicable when the host pipe has experienced significant sagging or deviation from the original grade. The service life expectations for pipe replacement by way of pipe bursting is equivalent to that for the replacement pipe type and material. FIGURE 34 Pipe bursting schematic (USDA Forest Service 2005). Pipe bursting can replace circular pipes up to 54 in. in diam- eter. The length is typically limited to 750 ft (Sterling et al. 2009). Applicability is not limited by culvert pipe type or con- dition. Replacement can be performed in live-flow conditions. Most favorable bursting projects involve pipes that were origi- nally installed by trenching or open cut because the fill material surrounding them is usually conducive to pipe bursting. The potential for feasible upsizing through pipe bursting depends on soil conditions, overburden cover, and other factors. FIGURE 33 Video inspection of CIPP liner after 23 years of service (left) and cut section of liner after 34 years of service (right) confirming excellent performance and no measurable deterioration (Macey and Zurek 2012).
