Guide to Use of Polyurethane Grouting to Reduce Infiltration

There are many options for repairing leaks in concrete structures. One of the oldest, yet least understood repair methods uses polyurethane chemical grouts that react with water to either bond with the concrete to form watertight, permanent seals or to become rigid, filling voids and stabilizing soil. According to the National Association of Sewer Service Companies (NASSCO), chemical grout was first developed in . Since that time, it has been used in sewers, manholes, tanks, vaults, tunnels, and many other applications all over the world.

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Studies show that 40% of groundwater infiltration in sewer systems enters through manholes. Some manholes require structural rehabilitation usually involving a spray, hand-applied or cured in place (CIP) lining system. It’s important for the municipality or the contractor installing any of these systems to realize that groundwater infiltration must be eliminated prior to the lining system installation. Too often, existing leaks in manholes are treated by applying a quick-set hydraulic cement over the active infiltration, which stops the leak temporarily, thus giving the lining system time to be installed. This temporary patch allows water to remain within the primary structure and can lead to a weakened bond or the failure of the lining system.

Installation Basics

Polyurethane chemical grouts are usually injected under pressure as a liquid resin into or in the vicinity of the leak. Once the resin contacts water, a chemical reaction occurs. Depending on the material formulation, the grout/water combination forms either an expansive closed cell foam or a gel. The foam created can be flexible and resilient (hydrophilic) or ridged, meaning the cell structure of the foam crushes when compressed (hydrophobic).

“As with any type of repair, choosing the right repair material has a great impact on the longevity of the repair,” said Scott Kelly, Technical Support Specialist for Prime Resins Inc. “There is not a single product on the market today that is a fix-all, do-all for repairing all leaks in concrete. Many products will temporarily fix a leak, but if applied correctly, most polyurethane grouting repairs are permanent.”

To break down the decision process, let’s look at the basic properties of both hydrophobic and hydrophilic chemical grouts. The properties of each type can be used to reduce the cost of installation and improve the quality of the repair long term.

Hydrophilic chemical grouts can produce either closed cell foam or a non-cellular gel when mixed with water. The reaction time is typically 30-45 seconds for foams and 12-15 seconds for gels. When activated, foams expand in volume between 5 –8 times. The volume of gel produced is relative to the ratio of water mixed with resin during installation. Hydrophilic Gels can shrink after cure in the absence of water. Hydrophilic chemical grout likes water and is able to bond to wet surfaces tenaciously; water-scavenging agents that seek out water as they react and allow the resin to work its way into water filled pores that exist in wet concrete surfaces. Hydrophilic chemical grouts are flexible and resilient after full cure and will allow movement to occur in the structure without damaging the seal or bond.

Hydrophobic chemical grouts require a catalyst that is blended into the resin prior to installation. The dosage of catalyst added to the resin controls the reaction time and the volume of foam produced. Using the maximum dosage of catalyst, (10% by volume) hydrophobic resins have an aggressive expansion; the reaction time is 10-12 seconds and expansion can be as much as 29 times in volume. Hydrophobic chemical grouts repel water after activation. When injected into a wet crack or joint hydrophobic resins can trap water in the pores of the wet concrete. This trapped water becomes a bond inhibitor. Hydrophobic resins cure rigid and do not recover from compression. If the structure moves there is good chance the cell structure will be damaged and leaks will reappear. Hydrophobic chemical grout is low viscosity and permeates loose and non-consolidated soils readily.

Knowing the basic differences in hydrophobic and hydrophilic chemical grouts is a crucial step in making the correct choice of repair material.

What to Do

If a leak repair project involves a non-structural defect in a concrete or masonry structure, a hydrophilic chemical grout should be used to seal the leak unless job conditions dictate otherwise.

Gels should be used only in below grade structures where either moisture from the interior (like in a manhole) or from ground water is present to keep the cured gel hydrated. Gels will shrink if water becomes absent, but provide a low-cost alternative to foams.

Foams are appropriate for above grade or below grade installation. They are typically 85% air filled after cure and have excellent elongation, compression and rebound for use in expansion joints, cracks, or any other non-structural defect in concrete structures.

Use the aggressive expansion of hydrophobic chemical grouts if repairing a gushing leak that is impractical to repair with milder expanding hydrophilic resins. In below grade structures, this is a good way to fill voids that may be present outside the structure. Once the leak is reduced to a manageable level, hydrophilic resin should be injected into the defect to back up the hydrophobic material.

Inject hydrophilic gel into gushing leaks neat or with a 1:1 water-to-resin mix ratio to shut down gushing leaks. This is a case where you push in as much material as possible as fast as you can. If a high volume pump is available, less material will be used to stop the leak because it reduces the dilution of the resin in the mass of water source.

Use “Activated Oakum” (dry oakum soaked in hydrophilic resin) to reduce the flow in gushing leaks. If the leak can be slowed, a hydrophilic resin may be used to complete the repair.

What to Avoid

Avoid installing gels in expansion joints or cracks that are subject to movement. Gels form a solid material with little or no cellular structure to disperse tension under compression. This tension can split the gel and damage the seal.

Avoid installing hydrophobic chemical grouts for repairing minor leaks in cracks or joints. The repair will be temporary.

Don’t get in a hurry when repairing tight cracks and minor leaks. These can be the most difficult to repair long term.

Conclusion

As our infrastructure ages, chemical grouting will continue to maintain its value as one of the easiest, most cost-effective and longest-lasting repair solutions available.

“If the right polyurethane chemical grout is chosen for your repair project and the correct installation techniques are used, the repair will actually outlast the structure,” Kelly said.

Contact us to discuss your requirements of catalyst for pu grouting. Our experienced sales team can help you identify the options that best suit your needs.

Editor’s Note:

Prime Resins is a manufacturer of polyurethane grouts and epoxies used for infrastructure repair and restoration. For more information about leak repair, visit the company’s website at www.primeresins.com. The site includes case studies and a learning center offering online tutorials.

Scope of Work:Injection of polyurethane chemical grout through probes to rehabilitate and seal below-grade pipes from an exterior application. 

Problem:Defects and joints in below-grade pipes allow for the infiltration of water into the pipe. This migration of water through defects that typically occur in pipe joints can cause an array of problems for the soil substrate and above-grade structures such as roadways, sidewalks, bridges and buildings. Access to the pipe is often limited and the rehabilitation or repair process often requires shutting down roadways, excavation and other time consuming options.

Solution:Injecting chemical grouts from outside the pipe is faster, cheaper and less disruptive than excavation and replacement.

Steps:

IDENTIFY THE DEFECTS

Identifying where the infiltration is occurring is the most important step in a successful rehabilitation application from outside the pipe. In scenarios where the pipe is large enough to access by crew, the identification process can be simple. Entry into the pipe along with a detailed log and measurement of location and the type of leaks present is required. If access by crew is not applicable, secondary techniques will be necessary to identify defects and their location. Video or CCTV can be taken from the interior of the pipe in order to locate and identify defects / leaks. GPR (ground penetrating radar) may also be used as a supplemental tool for locating voids, leaks and defects.

INJECTION PROBE PREPARATION

Once defects / leaks have been identified, probes can be installed to precise locations for the injection of Prime Resins chemical grout. For shallow depths, probes may be as small as 3/8” in diameter. For instances of greater depth or harder, more dense substrates, 1/2” to 3/4” probes may be necessary to effectively drive probes to the defect location.

Probes should be installed to a distance of approximately 6” – 12” from the defect in the pipe. Prime Resins recommends using drive points when installing probes to inhibit soil from blocking the end of the probe. When probes have been installed to depth, lift pipes 1” – 2” to allow for the release of the drive point. This will allow Prime Flex chemical grout to flow freely into the substrate.

PREPARING PRIME FLEX CHEMICAL GROUT

Both Prime Resins hydrophilic and hydrophobic chemical grouts may be used in probe grouting from outside a pipe defect. When using a Prime Flex hydrophilic grout (900 XLV, Hydro Gel SX), the material can be injected directly from its original packaging with a single-component pump. For hydrophobic grouts (910 and 920), a catalyst must be thoroughly mixed into the resin with a rotary drill and paddle mixer. Prime Resins recommends using a minimum 5% by volume amount of catalyst when sealing leaks outside a pipe.

INJECTING CHEMICAL GROUT

• Prime the pumping equipment with Prime Flex chemical grout to begin injecting material.
• Attach a Prime Resins flow control valve to the end of the injection probe, slowly open valve and begin pumping resin through probe into the area of defect.
• During the injection of material, monitoring from the interior of the pipe should be performed in order to ensure grout is traveling through the defect, creating the necessary seal. We recommend using CCTV or similar for monitoring.
• Once Prime Flex chemical grout is confirmed in the defect location, close the valve and allow the grout to fully react.
• Continue pumping material as necessary to create a seal around the pipe. It may be necessary to lift the probe from the bottom of the pipe to the top on either side of the pipe in order to get a complete seal around the defect or joint.

POST INJECTION

• Once the successful injection application has been complete, close valve and turn off pumping equipment.
• Disconnect valve(s) from probes and then flush pumping equipment with Prime Flex ECO Flush (seeFlushing a Single-Component Pump).
• Injection probes may then be removed or in some cases may be left in the ground and cut off below grade. Project owners can determine what is necessary.
• Excess foam on the interior of the pipe can be trimmed flush with an ordinary hydro or mechanical root cutter.

Safety Considerations:

• Carefully read MSDS/SDS prior to handling any chemical.
• Always wear safety goggles when drilling, grinding, flushing, injecting or handling resins.
• Always wear protective clothing, chemical resistant gloves and safety goggles at all times when handling resins. Blowouts can occur when injecting resins at high pressure.
• Be aware of potential electrocution hazards when working with power equipment in wet environments. Keep water away from electrical cords and electrical equipment.
• Make sure no loose clothing can come into contact with moving mechanical equipment.
• Follow all OSHA confined space entry requirements where applicable.
• Keep first aid kit (eye wash, bandages, etc.) present on site with easy access.

Materials List:

1. Prime Flex chemical grouts
2. Prime Kat (for hydrophobic)
3. Prime Flex ECO Flush
4. Water
5. Rags
6. 5-gallon pails (3)
7. Injection probes (schedule 40 or 80 iron pipe)
8. Prime Resins flow control valve
9. Prime Resins drive points
10. JIC adapters to connect to pipe

Equipment List:

Pump
Rotary drill
Hammer (for driving probes)
Rhino or equivalent pneumatic hammer (for driving probes)
Paddle Mixer

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