Structural Rehabilitation of Water Mains with Fast-set Polymeric Resin

Source: Environmental Science & Engineering Magazine
Author: Stephane Joseph, B.A. (Env.)
Date: March 2009
Download: View the Original Article Here (2MB PDF File)

In the fall of 2008, the City of Vaudreuil-Dorion, Quebec, an off island suburb of Montreal with a population nearing 28,000 people, rehabilitated a total of 1.4 kilometres of 150-mm and 250-mm-diameter cast and ductile iron water mains using a fast-set polymeric resin.

The work consisted of cleaning, drying and projecting several coats of NSF61-5 Polymeric Resin on the inside walls of the mains to obtain the required structural reinforcement. Since the resin sets in only a few seconds, it was possible to restore water service to customers on the same day of the work, without using a bypass system. The City estimated it saved several hundreds of thousands of dollars that would otherwise have been spent to replace the water mains.

Acuro is believed to be the first company to having successfully sprayed a structural liner inside a potable water main in North America.

More than 10,000 kilometres of mains have been rehabilitated over the last 10 years, mostly in Europe and Australia, using a spray-on, non-structural fast-set resin. Like cement or epoxy lining, this lining forms a physical barrier between the water and the main surface, preventing tuberculation and water quality deterioration.

However, “non-structural” means it does not guard the water mains against any leaks or breaks, and that was exactly the problem the City of Vaudreuil-Dorion wanted to solve. The water mains had lost most of their structural integrity due mostly to an aggressive soil. A total of six leaks and two breaks had occurred last year.

NSF-61-compliant Spray-in-Place- Pipe (SIPP) quick-set structural polymeric resin can be used for the rehabilitation of 2-inch-diameter and larger potable water mains. The polymeric resin is structural by definition, since it exceeds the physical requirements of the CIPP (Bag-Liner) ASTM F1216 standard (bag- liner), widely accepted in the industry.

The fast-set nature of the polymeric resin (gels in five seconds, tack-free in 30 seconds) allows return to service on the same day as the work, rendering optional the use of a bypass system. In this case, the City opted not to use a bypass while asking for residents’ co-operation, thus saving thousands of dollars (and headaches).

Acuro’s rehabilitation method aims at the structural reinforcement of distribution and transmission water mains, pipelines and conduits by installing a formulated fast-set polymeric resin liner, which is spray-formed to the original conduit by use of a hand spray or robotic sprayer. The polymeric resin is a thermoset material, cure-applied using impingement mixing under hydraulic pressure within the tube. The SIPP is continuous and tight-fitting.

The polymeric resin used for the project is corrosion-resistant; encrustation will cease and the water main C- Factor will not decrease over time. The C-Factor of a water main lined with resin is comparable to that of a PVC pipe. Polymeric resin shows a 10% elongation, which enables protection and service continuity in the case of a pipe break. In addition, the resin is resistant to all chemicals used in water treatment processes, including chlorine. Without VOCs, the resin has a 50-year life span. In fact, the resin passed the 100-year life span required for use in nuclear plants.

Another major benefit of the polymeric resin is that it is renewable; it can be sprayed over and over, year after year if need be. It also bridges small cracks and it provides a monolithic, close-fit lining to the host pipe, regardless of its diameter or shape. Non-NSF polymeric resin has also been used for many years to rehabilitate manholes, sanitary and storm sewers and surfaces. Polymeric resin is also an encasement system for lead, heavy metals and asbestos.

Work Procedures

In Vaudreuil-Dorion, a public tender was issued with both the bag-liner CIPP and SIPP specifications. The SIPP method was selected. Compared to the current trenchless CIPP rehab method used, SIPP is usually about 30% less expensive.

The scope included the rehabilitation of 350 metres of 150-mm and 1.2 kilometres of 250mm diameter water mains, along with the addition and/or replacement of main valves located on the mains to be rehabilitated.

Although some changes have been brought to the process, field operations were mostly based on the Code of Practice: In Situ Resin Lining of Water Mains from the UK water industry, and AWWA M28. Assistance from City staff was minimal. Field technicians had received the proper training and were certified by the manufacturer of the spray-on system.

Following site investigation and project planning with City staff, boil-water advisories were distributed door-to-door to customers, advising the nature of the project and warning about the water interruption between 8 a.m. and 6 p.m. As a courtesy, water bottles were offered to customers and arrangements with sensitive customers were also planned.

The customers’ service lines were closed right after 8 a.m. every morning. The access pits had been excavated at the existing valves’ location one or two days previously. A one metre section of the water main was cut and removed to get access from both ends of the water main. The main was inspected with a video camera and cleaning operations started immediately afterward. All video inspections were digitized on-site.

Following power cleaning, the main was dried with squeegee and com- pressed air. Another video inspection was conducted to validate the cleanliness of the water main prior to spraying.

A 3-mm thickness of resin was applied for the 150mm water main, and 5mm thickness for the 250mm water main to meet the Fully Deteriorated Pipe condition of the ASTM F1216 standard.

A robotic cutter was used to drill and reinstate the service lines, which were only partially blocked and easily visible, as their locations were also marked prior to lining. In addition to the printed record produced by the spray-rig soft- ware, confirming the volume (resin thickness) applied, a video inspection was also performed to validate proper installation, especially around the service line connection.

The water main was then disinfected as per AWWA standards, pressure and water tightness tests were performed and water samples were collected for laboratory analysis. The main was reconnected only at one extremity, creating an artificial dead-end until final test results were known. All tests results came back negative. Water service was always restored at the end of each day for sanitary use even though it was not considered potable. Backfilling and reinstatement of the road surface followed.

Lessons Learned

Lessons were learned from the application in Vaudreil-Dorion:

  • Waving of the resin on the main wall is amplified and appears worse than it actually is. During the last week of work, the outside temperature was down to –15℃. It was found that warming the compressed air used at the tip of the spray gun allowed for the proper dispersion of the resin.
  • As the resin was sprayed in both directions in the water main, coverage of the near surrounding of the service lines was excellent, preventing water infiltration between the liner and the main.
  • The water distribution system mapping was quite accurate. However, an additional access pit was required to negotiate a 90-degree bend that was not marked on the original drawings.
  • Because the 250mm-diameter water main was very fragile, a bypass was installed between hydrants only to regulate the pressure between the two zones, thus preventing water main breaks during the opening-closing operation of the valves.
  • Polymeric resin can be sprayed manually for larger transmission water mains. As an example and to meet the CIPP standard, calculations show that 14 mm of polymeric resin would be needed to structurally reinforce a 750mm-diameter transmission water main.

Structural Evaluation

A structural evaluation of the water mains had been done several weeks previously, using an electromagnetic probe to measure the wall thickness loss. The worst area observed showed a 55% material loss. For such an evaluation, no excavation was required, only the dismantling of the fire hydrants’ inner mechanism. However, the probe can also be used right after cleaning and prior to lining. Traveling at about 10 metres/minute, the probe is inserted from one end of the water main to the other to determine, in situ, the water main’s wall thickness loss, and thus its true structural condition.

CARE Program

To maximize water main rehabilitation budgets, Acuro has developed the CARE (Clean-Assess-Rehabilitate) program to provide assurance and guidance about the level of rehabilitation required for each water main. The work steps are as follows:

  • Clean the water main in the morning
  • Determine on-site the wall thickness loss using the probe.
  • Spray the desired thickness of poly- meric resin in the afternoon to provide a non- to a full-structural rehabilitation.

A step-by-step program is feasible since as many coats of resin as required can be applied to obtain the desired protection, as guided by the results of the evaluation.

Managers now have the option to rehabilitate the water mains in a non- structural fashion (i.e. 1mm thickness) and use the on-site evaluation to determine the water main’s true structural state and increase the resin thickness when required.

Conclusion

To date, the City of Vaudreuil-Dorion has not experienced any water quality complaints or leaks or breaks on the lined water mains, despite the polar temperatures of this winter.