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Injection grouting is a process of filling the cracks, open joints, voids, or honeycombs, in concrete or masonry structural members, under pressure with a material that cures in place to produce the desired results like strengthening a structure and prevent water movement.
Grout is a flowable plastic material and should have negligible shrinkage to fill the gap or voids completely and should remain stable without cracking, de-lamination or crumbling. There are different types of grouts such as cement grout, polymer-cement slurry, epoxy, urethane, and high-molecular-weight methacrylate (HMWM).
These grout materials are selected for particular type of concrete or masonry repair work based on the compatibility of the grout with the original material. If Proper grouting material is not selected, the desired objectives of the grouting process would not be achieved.
Grouting Material Preparation
Only that quantity of epoxy is mixed which can be used before gelling of the material, otherwise pressure injection becomes considerably difficult. During the batch mixing process, the components of the epoxy are mixed in a fixed quantity using a mechanical stirrer, such as a paint mixing paddle.
In the more advanced continuous mixing system, the two liquid adhesive components are passed through an automatic mixing head after the pumping just before leaving the gun.
This system allows the use of fast setting adhesives that have a short working life. After the injected epoxy has cured, the projected part of surface seal is removed by grinding or other appropriate means.
1. Drill Ports
Drill short holes, which is also known as ports, into the cracks/ openings in order to be used as entry and venting terminals. Minimum diameter and depth of ports are 2.5cm and 5cm, respectively.
Spacing between holes is 150 mm c/c for finer cracks to 300 mm c/c for others. The spacing of ports is usually kept greater than the desired depth of grout penetration, but it may be adjusted based on judgment and requirements for a particular project.
2. Seal Cracks Between Ports
The crack /opening surfaces between ports are sealed by applying epoxy, polyester, strippable plastic surface sealer for low injection pressures, or cementitious seals if surface appearance is important to the surface of the crack.
Time required for hardening of seal depends upon the type of material used. To stiffen the surface seal, the cracks are usually routed 6 mm in width and 13 mm in depth.
Sometimes, the crack can be cut out to a depth of 13 mm and width of about 20 mm in a V-shape, which is then filled with an epoxy to get a flush surface. If cracks pass through the structure, such as a wall, the surface seals and ports are applied on both sides.
Openings may be sealed by plugging with cloth or fabric that allows passing of water or air but retaining of solids. Paper and other materials that remain plastic are not suitable for this purpose.
3. Cleaning Ports and Cracks
Before grouting, flushing is done with clean water to obtain the following objectives:
- To wet the interior surfaces for better grout flow and penetration.
- To check the effectiveness of the surface sealing and port system.
- To gather information on grout flow patterns and details of interconnections of voids / discontinuities in the mass.
- To familiarize the grouting crew with the situation.
Full crack cleaning may not be possible in practical situations and judgment must be used to decide the extent of this cleaning.
4. Make Grouting Hose Connections
When the ports are drilled after sealing the openings and the grout pressure is up to 350 kPa, a hand-held, cone-shaped fitting on the grout hose is sufficient.
For larger grout pressures, short pipe nipples are connected in to the holes to obtain grout hose connections. The method of installing entry and vent ports in case of V-grooving of the cracks is to drill holes 20 mm in diameter and 13 to 25 mm deep below the groove at the required spacing. A pipe nipple or tire valve stem is usually bonded with an epoxy adhesive.
The method commonly used in case of rectangular grooves is to use a flush fitting has an opening at the top for the adhesive to enter and a flange at the bottom that is bonded to the concrete face.
Third method is to use special gasket devices which can be directly fitted on to the discontinuities / openings in the surface seals.
5. Grouting Process
Grouting is started at one end of a horizontal opening or at the bottom of a vertical opening. It is continued until grout appears at the next port or the surface seals of cracks bulge out, after which the grouting operation is shifted to the next port.
The port valves from where the grout is coming out are plugged before moving to the next injection location. Grouting is usually started with a relatively thin grout, thickened as quickly as possible to the heaviest consistency that can be pumped without blockage.
Extreme caution must be exercised when injecting cracks that are not visible on all surfaces. For injection of the epoxy, hydraulic pumps, paint pressure pots, or air-actuated caulking guns are generally used.
The pressure used for injection must be selected carefully and it must not be excessive. For vertical or inclined cracks, the injection process must 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 has been completely filled.
6. End of Grouting Process
An indication of full filling of the crack is that the pressure does not drop. Epoxy injection requires a high degree of skill for satisfactory application of the technique. The atmospheric temperature at the repair site is also an important consideration.
Injection Grouting of Massive Structures
For massive structures, the procedure consists of drilling a series of holes, 20 to 100-mm diameter, at a spacing of 1.5 m along the crack. In a recently developed method, a bag is wrapped all along the member and the liquid adhesive is introduced at the bottom and is sucked by a vacuum pump at the top, or epoxy is injected in the cracks from one side and pulled from the other side.