Chemical Grouts for Inflow & Infiltration Rehabilitation
June 29, 2011Every minute of every day, millions of gallons of groundwater, surface water or storm water are flowing into the nation’s sewer systems. This inflow and infiltration (I&I) costs consumers billions of dollars annually. Particularly in wet weather climates, the cost can be higher when you consider the burden placed upon the treatment facilities due to the increase of additional water that still needs to be considered wastewater and treated as such. I&I can impact the ability of the treatment facility to treat the municipal wastewater, causing overflow problems from the system. Backups in basements and manhole overflow onto city streets may result. Consequently, the treatment process is disrupted and untreated sewage can spill into the environment.
Overflow events can be problematic for communities; it’s not only a health risk, but it is a violation of federal and state law. This excess water is also the reason for additional operating cost, over taxation on the infrastructure and unneeded stress on the pumps and sewer lines that shorten the life expectancy of the system. Finally, communities with failing sewage systems or systems that do not meet regulations or guidelines will not be eligible for grants or low interest loans through government agencies.
Solution: Reducing Inflow & Infiltration
Municipalities, engineers and contractors are under constant pressure to locate, repair and reduce inflow and infiltration to minimize the burden and financial replacement costs that are placed upon the aging sewage and treatment systems. I&I is a result of defects that occur in piping, manholes, lift stations and storm drains allowing groundwater, sand and other debris to enter the systems and flow to the treatment facility. Freeze-thaw cycles, heavy traffic and ground erosion can cause stress on concrete, eventually opening joints and creating a path for water infiltration.
In today’s market, there are several options for repairing active water leaks in concrete structures. There are waterproof concretes and water-stop materials that have their uses in underground structures for temporarily stopping infiltration. A more permanent solution is the use of chemical grouts. Polyurethane chemical grouts have been used for more than 50 years with great success and still prove to be one of the most cost-effective solutions to stopping infiltration. Studies show that more than 40 percent of inflow and infiltration occurs through manholes. Many of these structures will need complete structural rehabilitation, including a spray applied liner, a hand-applied cementitious liner or a cured in place liner. However, before a lining system can be installed, the active water leaks must be stopped. Active water leaks can penetrate cementitious and epoxy liners, inhibiting bond and causing failure of the lining system. Chemical grouts are designed to seal the structures. Owners and contractors should know which grout will meet their needs.
Polyurethanes: Hydrophobic vs. Hydrophilic
Polyurethane chemical grouts are water activated and can possess two distinctly different properties. Hydrophobic grouts will repel water and push it away. When fully cured, they typically form a rigid system. However, hydrophobic grouts are now available in a flexible foam variation. Because the water is not absorbed by the grout, the water is forced to move to another location around the structure that may open other avenues for the water to infiltrate. Hydrophobic grouts have great expansion properties, typically 20 times their original volume; a low viscosity that enables it to flow easily through loose soil (making it an ideal soil stabilization material); and a quick set time for filling voids and stopping active leaks. All this saves down time and allows structural rehabilitation to proceed.
Hydrophobic chemical grouts are best for filling large voids on the outside of underground structures where the soil has eroded, settled or collapsed. The grout can be injected through the concrete by drilling through the wall of the structure and pumping the grout to the backside. Another method to fill this void is by driving an injection pipe down from the top surface and pumping the grout into the void until the active leaks have been stopped. If either of these methods only slow the leak, it may be necessary to finish the repairs by injecting a hydrophilic grout into the cracks to completely seal the concrete structure.
Hydrophilic grout will absorb the water from the concrete or soil. It offers a tenacious bond with the substrate by absorbing water in the cracks within the substrate. Hydrophilic grouts form a flexible seal that moves as pressure and temperature change, allowing for expansion and contraction of the material. So, for non-structural defects in the concrete and where moisture is present to keep the gel hydrated, injecting a hydrophilic grout material may be your best solution. Small cracks and small leaks are the most difficult to repair. It takes time to chase and fill all the cracks.
If the right chemical grout is chosen for your inflow and infiltration repair project and the proper equipment and installation methodology is used, a cost-effective and long-lasting solution will result. It should be noted that chemical grouts have their limitations as well; temperatures, UV rays, pH levels and hydrostatic pressure can have an adverse effect on the overall performance in the effectiveness of the application. Before beginning a repair project, consult the material manufacturer for the proper recommendations. For structures that are being lined with a cementitious, epoxy or urethane system, additional prep work will have to be completed before installation. If injector nozzles are installed, they will need to be cut off and grounded down at the surface. The excess grout that has flowed on the walls will also need grounded down, to assure a better surface for the lining system to bond to.
Innovative Products & Application Methods:
Sauereisen features both variations of hydrophobic urethane grouts. One version offers rigidity while the other is more flexible. Hydroactive Polyurethane Grout No. F-370 is a non-flexible, hydrophobic polyurethane grout that is applied by injection and specified to repair large voids in concrete. It also provides soil stabilization around underground structures to stop water infiltration and active leaks. It is also recommended for use in tunnels, manholes, sewer lines, tanks, dikes and dams. F-370 has excellent chemical resistance and may be used in a wide range of chemical environments. Sauereisen’s Grout No. F-370 is packaged in a 5-gallon unit consisting of a pail of resin and a pint can of a catalyst. Packer injection nozzles are available upon request.
New to the Sauereisen family of rehabilitation materials is the F-370 dual-cartridge (20-ounce) system. This dual-cartridge system is a hydrophobic (flexible) material that is ideal for smaller cracks and sealing joints in basements, foundation walls, sub-surface concrete structures, parking structures, sewers and manholes. The 20-oz. size offers convenience because there is no need for pumping equipment, hoses or injection nozzles. The only equipment needed is a dual cartridge gun that is available at your local equipment supply store. The 20-oz. dual cartridge is packaged with an application nozzle.
Inflow and infiltration will continue to be a challenge to U.S. wastewater infrastructure. However, knowing the causes and, more importantly, the solutions to this problem will help municipalities, engineers and contractors to repair and reduce I&I and reduce their economic and environmental impact.
John E. Davis is an inside sales and marketing specialist at Sauereisen Inc., based in Pittsburgh.