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Injection Grouting Facts

The Pressure Injection System
The Pressure Injection System can be used for injecting cracks, cold joints, expansion joints and for soil stabilization. The system can be used to stop gushing water, to seal minorseepage, to regain structural integrity and to waterproof and strengthen almost any concrete ormasonry structure from the positive or negative side, below grade, above grade and under water.The system includes epoxy injection techniques as well as polyurethane injection techniques.The following introduction focuses on the high pressure injection in conjunction with mechanicalpackers. Mechanical packers eliminate many problems of the surface ports including bondfailure at pressures above 300 psi and inaccessibility in wet, and water pressured areas. Highpressure injection through mechanical packers opens a new dimension of possibilities to solve joint and crack related problems.
Resins and equipment for low and high pressure injection, surface port and mechanicalpacker injection methods and systems are available now a day. There are some standardprocedures that can be followed on most jobs. The following is a short introduction.
It is recommended to inject at a time when the cracks or joints are at the widest aspect of their moving cycle. The reason is that sealants perform better in compression than in tension.This is of great importance when extreme movement is expected. In addition to the goodpenetration, the material won’t experience any tension, since the cracks are already at the widestaspect of their moving cycle.
Besides crack injection it is also possible to inject polyurethane grout to the back side of awall into the soil thus creating a grout curtain. This procedure is necessary when well definedcracks, joints or openings of any kind cannot be detected but moisture infiltration is evident.Another option is injection of the void between the structure and an existing membrane that hadinitially been installed to prevent water leaks, but failed. Membrane failure is a common cause of below grade water leaks.
The Pressure Injection System has been proven to be a superior system in correctingthose failures with ease by injecting from the negative side. No digging is necessary. Voids in thestructure can be sealed, defective membranes can be fixed and even water pockets behind thestructure can be effectively filled to minimize hydrostatic pressure. The injected soil will becompacted and stabilized thus reducing water accumulation behind the structure and shifting of loose soil. The Pressure Injection System has been proven to be extremely versatile, reliable andeconomical in resolving water related and structural problems.
The basic steps for the injection procedure are:
1. Clean surfaces
2. Drill injection holes
3. Insert injection packers
4. Flush crack, if necessary
5. Resin injection,
6. Cleanup
Cleaning of the surface helps the technician to identify the exact location and the width of thecrack to be injected. Sometimes the concrete surface is hidden under a surface of mineraldeposits left from long-term water leakage. Items that obscure the crack should be removed,because the crack must to be seen clearly in order to layout the drilling patterns for the injectionholes.
In order to inject the resin into the crack, it is necessary to install injection ports, also calledmechanical packers or just packers. While it is common to use surface injection ports for somelow pressure epoxy injection in dry areas, it is recommended to use packers for polyurethaneinjection and high pressure epoxy injection. Surface ports will not stick to wet surfaces and theydo not tolerate high injection pressures. Quite the opposite is true with mechanical packers. Themetal-rubber type packers are made for pressures up to 5000 psi in wet and dry structures.Before drilling the injection holes, locate rebar and conduit, and plan the pattern to minimizedamaging the bit during drilling.
It is advisable to use a high quality rotary hammer. The diameter of the average injection holewill be 16 mm. The angle while drilling should be approximately 45 degrees or less to thesurface and towards the crack. The depth of the drill hole intersecting the crack should besomewhere close to the middle of structure, if possible. Holes deeper than 18″ are usually notrequired even if the concrete being repaired is more than 36 inches thick, as long as adequatepumping pressure is available and material is contained during injection. Holes should always bestaggered from one side of the crack to the other. This assures a higher percentage of holesintersecting the crack, even if the angle of the crack within the concrete is not perpendicular tothe surface. No two cracks behave just alike. In some instances a crack will fill from just a fewinjection packers.
The distance of the drilled holes to each other usually varies from 150mm to 500mm accordingto the width of the crack. (Rule of thumb: 300mm) The wider the crack, the further apart are thedrill holes. Experience helps in deciding how far apart to drill the injection holes.If the concrete thickness is 150mm or less, do not attempt angle drilling, set the packers straightinto the face of the crack. This will help to minimize spalling in these concrete sections.
Place packers in the previously drilled hole, so that the top of the rubber sleeve is below theconcrete surface. If the packer can’t be pushed into the hole, tap it in. Tighten the packer with awrench as tight as necessary. For critical areas such as corners and badly deteriorated surfaces,long versions of the regular packers should be used to allow a deep insertion of the expandablerubber sleeve.
In some circumstances, it can be very useful to flush the crack with water to improve thesubsequent penetration of the injection resin into thicker walls. Flushing helps to detect blind drill holes, or lost continuity of a crack. The procedure starts at the lowest packer on a verticalcrack, or at the narrowest part of a crack of a horizontal surface and proceeds from packer topacker in sequence. During flushing, it is advisable to disconnect zerk fittings from packers thatare not connected to the pressure line and thereby creating an exit for surplus liquid. Aftercompletion of flushing, prepare for the resin injection. Flushing is not advisable for epoxyinjection.
When all preparation work is completed, make sure the injection pump is in good working order.All equipment that comes in contact with the chemicals must be absolutely dry. Choose theproper resin for the correct application. The nature of the crack/joint and the conditions at the jobsite determine the choice of material. Mix resins in accordance to specifications andrecommendations. Load the resin hopper and charge the pump, hose, and gun. Open the valve onthe gun, and allow all remaining solvent to pass while watching for the resin to appear. Catch allsurplus material and solvent in a waste container. Keep the hopper covered in wet environments,especially if it is raining or water is dripping from the ceiling in an enclosed environment.The technician should be carefully watching three points of reference:
1. The crack /packer- for resin flowing out of the work face
2. The pressure line – for pump pulsations indicating resin flow
3. The gauge (if available) – for actual injection pressure applied
Begin the injection at the point of highest resistance to ensure good penetration and minimal lossof chemical. This is usually the lowest point on a vertical crack and the narrowest area on ahorizontal surface. First, fill the drill hole, and then start slowly injecting the crack.Holding the pressure line allows the operator to feel the pump pulsations. The technician may tellfrom the hose vibration how well the material is flowing into the crack. If a pressure gauge isavailable, the pressure should be monitored and kept in a range that is just enough to allowsufficient flow of material. This procedure helps to minimize unforeseen events like suddenspills of material, blown out ports or spalling of defective concrete. If the crack surface exhibitsimmediate free flow of resin while working the first packer, pause for a few minutes. In mostcases the resin will react fast enough with the water and expand rapidly. The resulting resinproduct will heal the crack and provide a surface seal to contain the material to follow. Afterwaiting for approximately three to five minutes start pumping again. If the resin continues toflow freely out of the crack, stop pumping and apply a surface seal over the crack with rapidsetting cement Renderoc Plug. When the soaked material comes in contact with water it startsto expand, creating a fast, permanent surface seal. Resin may still flow from pinholes in thepatch, but do not be concerned as long as the majority of the resin is contained. A small amountof leakage is beneficial because it shows the extent of resin travel.
Extremely wide cracks should be covered with a surface seal prior to injection in order to containthe resin until cured. Under proper pumping conditions in active leak injection, the followingsigns should be observed in the order listed:
1. Water displaced from the crack by the resin
2. Water and resin mix appearing at the crack 
3. Pure resin from the crack 
It is helpful to disconnect the zerk fitting from the packers ‘ahead’ to allow free port to porttravel. Proceed pumping until the resin has travelled to the next packer, and is oozing out slowly on the visible side of the crack. Once you are assured that the resin has reached the next injectionpacker, attach the zerk fitting. Shut-off resin flow, disconnect your pressure line and proceed tothe next packer. After injecting a couple packers, return to the first packer and inject again. Someof the packers will take more grout, filling up more of the crack and creating higher density crack filler. Some contractors re-inject up to three times. Continue in this fashion until the crack iscompletely filled.
Once the injection work is completed, a good and thorough cleanup is essential, because once theresin hardens, it is almost impossible to dissolve it. Any resin spilled must be cleanedimmediately before the resin sets. The packers can usually be removed within 24 hours and theholes should be patched. If desired, an electric grinder can be used to remove excess cured groutthat flowed out the crack.