A GeoPolymer Solution: Controlling Stormwater Infliltration in California

Having suffered consistent long-term exposure to the excessive groundwater flows, severe corrosion, several offset joints and even partial collapse of the corrugated metal pipe (CMP) in numerous places, the City of El Cajon, Calif., knew it needed to do something. The elements had inflicted too much damage, and the City’s stormwater system was in dire need of repair.

As a result, the City put its 2013 Sewer and Storm Drain Rehabilitation project out to bid with the objectives to fix its infrastructure and to optimize its capital improvement program with long-term solutions at an affordable cost to its taxpayers. With a wastewater fund of under $6.5 million for the 2013-2014 year, the City was pleased when Inland Pipe Rehabilitation LLC was the awarded the project with a bid under the engineer’s estimate.

Project Scope

The initial scope of the project was approximately 3,000 lf of pipe rehabilitation with diameters ranging from 6 to 48 in. and positioned well beneath the narrow streets and pristine yards of upscale residential neighborhoods. The project was originally slated to use the cured-in-place pipe (CIPP) lining system, but understanding that the cost of CIPP rehabilitation grows dramatically with each increase in diameter, the City decided to review alternate technologies, as well.

After a thorough analysis, the City decided to open up its specifications to allow centrifugally cast geopolymers as an option. As such, the IPR EcoCast system using GeoSpray geopolymer mortar from Milliken Infrastructure Solutions was employed for the pipes larger than 36 in. in diameter while the CIPP process was performed on the smaller diameters. Work commenced in April 2014. The advantage of having multiple repair options within a single contract allowed the City to utilize the most economic repair options based on pipe diameter. As an additional benefit, this decision not only provided a structural solution to the City’s badly deteriorated infrastructure, but also allowed it to allocate funds to identify other deteriorated stormwater lines in need of repair.

Challenges

As the rehabilitation program commenced, one of the first challenges was to work within lane closures and a traffic control program laid out by Caltrans for not only the sewer by-pass but also for the installation program itself. The work areas identified were approximately 25 ft in length by 8 ft in width. While there were buffer and transition zones for lane closures provided to guide traffic around the work area, there was still little room for the necessary equipment for the rehabilitation. Fortunately, the footprint of the spin-casting system used by the installer provided a great amount of flexibility to work around the constraints. Using a self-contained equipment package that included power, air and water, IPR was able to work within the designated borders of operation. By using a just-in-time material management system, the contractor was able to bring the materials onsite as needed, which also reduced the area needed.

“EcoCast is ideal for a variety of applications and is especially effective for stormwater and sewer line repairs similar to the El Cajon project,” explained IPR vice president Rob McCrae. “There were several challenges and extenuating circumstances, including many sections that required extensive prep, patch and sealing work. We were confident the EcoCast process would be effective, despite the many challenges.”

According to McCrae, EcoCast is designed specifically for large diameter projects and effective for materials that have separated, dropped or have curves, making it an ideal rehabilitation option for the severely corroded and structurally compromised El Cajon job. The vast majority of pipes ranging in sizes from 36 in. to more than 10 ft in diameter can be rehabilitated using this method. With less installation risks than other lining rehabilitation methods, and given the confined space jobsite restrictions of this residential area of El Cajon, the project owner was convinced that IPR had recommended a solid, effective solution.

The Rehabilitation Process

The process began with thorough cleaning of the inside of the severely corroded CMP. “To assure that proper adhesion occurred, the interior of the pipe was thoroughly cleaned using a high-pressure washer ranging from 3,500 to 5,000 psi,” McCrae said.

A fast-setting hydraulic cement applied directly to the damaged sections of the CMP was necessary to stop flowing water and repair leaks. Chemical grouts were also applied at several junctures to stop larger amounts of infiltration.
Once cleaned, IPR then employed the process for applying the cementitious EcoCast geopolymer liner, as determined by findings of the engineers reports outlining the thickness the liner needed to be to effectively repair the structure of the pipe. In this case, a minimum thickness of 1 in. was required, using the GeoSpray geopolymer material mixed with appropriate amounts of clean water. The liner was then applied to the inside of the pipe using a spin casting process.

“Beginning at the downstream side of the pipe, the oscillating EcoCast spin cast assembly was placed inside the pipe, along with the product delivery hose, retraction chain, air hose and electric power line,” explained IPR project manager Mike Espinosa. “A direct-drive electric motor moves the entire assembly at a predetermined speed, depending on the thickness of cementitious liner required for various sections. The application process is monitored continuously and adjusted accordingly, based on engineer inspection reports. The pump delivers material at a consistent rate and pressure, and has a multiple built-in alarms that detect whether too much or too little material is being delivered. The water ratio is also carefully monitored and must be maintained on a consistent basis.”

Once the liner achieves initial curing — only a matter of hours for the various sections of the El Cajon job – full stormwater flow was released within 12 hours of the application.

The entire project was concluded in multiple phases. In fact, the City identified additional pipes that were in need of repair and due to the cost-savings, was able to have these overhauled, as well.

“We were able to complete the CMP rehabilitation completely, successfully and cost-effectively with only minimal disruption to the neighborhood,” McCrae says. “We were able to overcome a variety of challenging conditions and save the City a lot of aggravation. It turned out to be the ideal solution for repairing this severely corroded section of stormwater pipe.”

Finally, because of the cost-effective joint solution offered by IPR to the City, the project was extended to include an additional 2,250 lf of rehabilitation work ranging from 18 to 40 in. following the completion of the original scope.

Fil Borroni is western states sales manager at RePipe California. John Hepfinger is global market manager with Milliken Infrastructure Solutions.