Injection grouting is a process that involves filling cracks, open joints, voids, or honeycombs in concrete or masonry structural members under pressure with a material that cures in place to achieve the desired results. The main objectives of injection grouting are to strengthen a structure and prevent water movement.
Grout is a type of flowable plastic material that should have negligible shrinkage to fill the gaps or voids completely. It should also remain stable without cracking, de-lamination or crumbling. There are various types of grouts, including cement grout, polymer-cement slurry, epoxy, urethane, and high-molecular-weight methacrylate (HMWM).
Choosing the right grouting material is crucial as it directly impacts the effectiveness of the repair work. The selection of grouting material is based on the compatibility of the grout with the original material of the structure. If the proper grouting material is not selected, the desired objectives of the grouting process may not be achieved. Therefore, it is essential to choose the right grout to ensure the successful completion of the repair work.
Grouting Material Preparation
The quantity of epoxy that is mixed must be carefully controlled to ensure that it is used before it starts to solidify. If the epoxy begins to gel, it can become difficult to inject it under pressure. To mix the epoxy, a mechanical stirrer, such as a paint mixing paddle, is used to combine the two components in a fixed quantity.
In more advanced systems, a continuous mixing process is used. In this process, the two liquid components of the adhesive are pumped through an automatic mixing head just before they are applied with a gun. This allows fast-setting adhesives with a short working life to be used.
After the epoxy has been injected and cured, any excess material that protrudes from the surface needs to be removed. This can be done using grinding or other suitable methods to create a smooth, even surface.
Grouting Procedures
1. Drill Ports
When dealing with cracks or openings, it can be necessary to drill short holes, also known as ports, in order to create entry and venting points. These ports typically have a minimum diameter of 2.5cm and a minimum depth of 5cm.
The spacing of the ports is dependent on the severity of the cracks, with a spacing of 150mm c/c used for finer cracks and 300mm c/c used for larger ones. Additionally, the spacing of the ports should be greater than the desired depth of grout penetration.
However, there may be instances where the spacing of the ports needs to be adjusted based on the specific needs and requirements of the project at hand. Ultimately, judgment and careful consideration should be exercised when determining the appropriate spacing for ports in order to ensure the best possible outcome.
2. Seal Cracks Between Ports
The sealing of crack or opening surfaces between ports can be achieved by various materials such as epoxy, polyester, strippable plastic surface sealer or cementitious seals, depending on the desired injection pressure and surface appearance. The hardening time of the sealant depends on the type of material used. To strengthen the surface seal, cracks are typically routed to a width of 6 mm and depth of 13 mm.
In some cases, a V-shaped section measuring about 20 mm in width and 13 mm in depth is cut out of the crack and then filled with an epoxy to achieve a flush surface. When cracks pass through a structure like a wall, surface seals and ports are applied on both sides to ensure complete sealing.
Openings can also be sealed by plugging them with cloth or fabric that allows water and air to pass through but retains solids. However, materials like plastic paper that remain plastic are not suitable for this purpose. It is important to choose the appropriate sealing method and material based on the specific needs of the project.
3. Cleaning Ports and Cracks
Prior to the grouting process, it is necessary to flush the area with clean water. This step serves multiple purposes that are crucial for the success of the grouting project. Firstly, it ensures that the interior surfaces are properly wetted, which aids in the flow and penetration of the grout. Secondly, the flushing process allows for the effectiveness of the surface sealing and port system to be checked. This step is important to ensure that the grout will properly fill all voids and discontinuities in the mass. Additionally, it provides valuable information on grout flow patterns and the interconnections of voids and discontinuities. This knowledge can be used to make informed decisions throughout the grouting process. Lastly, the flushing process helps familiarize the grouting crew with the situation, allowing them to better understand the specific challenges and nuances of the job at hand. It should be noted that while full crack cleaning may not always be possible, the grouting crew must exercise judgment to determine the extent of cleaning necessary for optimal results.
4. Make Grouting Hose Connections
When drilling ports after sealing openings and reaching grout pressures up to 350 kPa, a hand-held, cone-shaped fitting on the grout hose is sufficient. However, for larger grout pressures, short pipe nipples are needed to connect to the holes for grout hose connections.
When V-grooving cracks, holes with a diameter of 20 mm and a depth of 13 to 25 mm are drilled below the groove at the necessary intervals. A pipe nipple or tire valve stem is then bonded with epoxy adhesive.
In the case of rectangular grooves, a flush fitting is used, which has an opening at the top for adhesive entry and a flange at the bottom that is bonded to the concrete face.
Alternatively, special gasket devices can be used, which are directly fitted onto the discontinuities or openings in the surface seals.
5. Grouting Process
Grouting typically begins at one end of a horizontal opening or at the bottom of a vertical opening. The process continues until grout is visible at the next port or until the surface seals of cracks bulge out, indicating that the grout has effectively filled the voids. At that point, the grouting operation is then shifted to the next port to continue the process along the desired path. This sequential approach ensures thorough grouting and proper sealing of cracks or openings.
Fig. 4: Schematic Presentation of Injection Grouting
When injecting grout into cracks, it is important to start with a relatively thin grout and gradually thicken it to the heaviest consistency that can be pumped without blockage. The port valves from where the grout is coming out should be checked for any plugs before moving to the next injection location. Care must be taken when injecting cracks that are not visible on all surfaces.
To inject epoxy, hydraulic pumps, paint pressure pots, or air-actuated caulking guns are commonly used. The pressure used for injection should be carefully selected and not excessive. When injecting vertical or inclined cracks, the process should begin by pumping epoxy at the lowest level until the epoxy level reaches the entry port above. The lower injection port is then capped, and the process is repeated until the crack is completely filled.
6. End of Grouting Process
One way to determine if a crack has been fully filled is by monitoring the pressure during the injection process. If the pressure does not drop, it is a good indication that the crack has been successfully filled. However, achieving this result requires a high level of skill when applying the epoxy injection technique.
The application of epoxy injection involves injecting a resin material into the crack under pressure. This requires a precise and controlled technique to ensure that the material is properly distributed and adheres to the surrounding surface. Therefore, it is crucial to have a skilled technician perform the injection process to achieve a satisfactory result.
Apart from skill level, the temperature at the repair site is also an important consideration for successful epoxy injection. The atmospheric temperature can affect the curing time of the resin material, which can impact the final strength and durability of the repair. Therefore, it is necessary to take into account the temperature conditions during the repair process to ensure optimal results.
Injection Grouting of Massive Structures
When dealing with large structures, a common procedure for repairing cracks involves drilling multiple holes spaced 1.5 meters apart along the crack, with diameters ranging from 20 to 100 millimeters. However, a new method has been developed which involves wrapping a bag around the entire member and introducing liquid adhesive at the bottom. This adhesive is then sucked up through the cracks using a vacuum pump located at the top. Another approach involves injecting epoxy into the cracks from one side and then pulling it through to the other side. These methods are collectively known as injection grouting and are used to effectively repair cracks in massive structures.
Fig. 6: Injection Grouting