Injection grouting is usually carried out from the surface and is the common method for filling cracks, open joints, and interior voids with a material that cures in place to produce the desired results. . Grouting can strengthen a structure and can prevent water movement. Proper grouting material is to be selected for a particular project to achieve the desired objectives, while cores are tested to ensure quality control.
Short entry holes (called ports) are drilled into the opening having a minimum diameter of 25 mm and a minimum depth of 50 mm. These holes are drilled from face of the concrete at spacing of 150 mm c/c for finer cracks to 300 mm c/c for others (to be used as entry and venting terminals). 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. 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. 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. 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. 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. Before grouting, flushing is done with clean water to obtain the following objectives:
1. To wet the interior surfaces for better grout flow and penetration.
2. To check the effectiveness of the surface sealing and port system.
3. To gather information on grout flow patterns and details of interconnections of voids / discontinuities in the mass.
4. 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. 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.