Concrete Repair Part Two
The Process of Structural Crack Injection

When considering structural crack injection to repair damaged concrete you must first analyze the crack to determine if an epoxy repair is appropriate. For dormant cracks in a structure that is to be rehabilitated, structural crack injection is recommended. This method can also be used to repair active cracks in concrete or wood but it is also necessary to install joints to prevent further damage from occurring along the crack line.

Because structural epoxy has excellent adhesion to both concrete and wood surfaces, and has superior physical properties, epoxies are capable of restoring the cracked member to its pre-crack strength. If properly installed, any new failure of the structure will typically occur in the concrete or wood, not within the epoxy.

Materials

Proper injection requires the right equipment. The required materials are a capping epoxy, injection resin or paste, injection ports, dispenser, wire brush, protective eye glasses, gloves, tongue depressors or putty knife and proper injection kit or mixer nozzles with retainer nuts and check valves.

For cracks where both sides can be sealed, consider the injection epoxy to use based on the width of the crack you will be injecting and the substrate temperature. Some epoxies are designed for larger cracks while others are intended for use on hairline cracks. If you are repairing a blind wall (one that is only accessible from a single side), make sure you choose a product that will prevent the material from running out of the blind side.

Prepping the Crack Face

Using a wire brush, gently clean the wood or concrete surface surrounding the crack, so that the crack is not plugged with debris, and that the surface near the crack will bond well to the epoxy paste. Be careful not to plug the crack entry with any concrete dust or foreign matter when preparing the crack face.

Structural Crack Injection of walls, columns and vertical surfaces can be described in three main steps:

First, the injection port is mounted along the crack-line and the crack is "capped" using a gel or paste epoxy. Second, the cap is allowed to cure and an appropriate injection epoxy is selected. Third, the epoxy is injected from one end of the crack to the other, one port at a time. The process is repeated until the crack is completely injected.

Mounting Ports & Capping the Crack

Affix the ports to the crack at a spacing approximately the same as the depth of the cracked member. The port spacing may be varied slightly to locate open spots along the crack face or it may be reduced if blind-wall run-out is a potential problem.
 

There are several methods of attaching the injection ports to the surface of the crack. The most effective method of attachment is to dab a small amount of the epoxy paste or gel onto the “feet” of the injection port. Then stick it in place over the crack face, being careful not to plug the port’s access to the crack with epoxy.
 

When excessive pressure is required to properly inject the crack, it may be required to attach the port using the drill in method. This is done by drilling a hole (1/2” - 3/4” diameter) at the port location, inserting the port and then sealing with the epoxy paste. Paste epoxy is then dispensed over the crack and smoothed over with a putty knife, or similar tool. Care must be taken to seal the entire length of the crack to hold them firmly in place and prevent leaking under pressure during injection. Take special care to see that the “feet” of the port are fully covered.

The epoxy paste must be allowed to cure prior to starting the injection. Time of cure is dependent upon both substrate temperature as well as epoxy material used.

Injecting the Crack

There are two widely used strategies for crack injection. One very simply involves starting at one end of the crack (the bottom if it is a vertical crack) and injecting until good clean epoxy is coming out of the next port. The operator then plugs the first port, and begins injection at the second port, until clean epoxy runs from the third port, and so on. Alternatively, injection can be started at the widest part of the crack and worked into the thinner crack regions.
 

It is critical that the applicator make certain that the injected epoxy be on ratio and well mixed. The cartridge system does much to simplify the assurance of this. However, if an air tool is being used care should be taken not to run the regulated air pressure to the dispenser above manufacturer's recommended limits, or cartridge leakage may occur.

Also, the first material dispensed from the cartridge must be discarded. This is to account for the fact that either epoxy or curing agent will precede the second component initially coming from the cartridge.
It is a good idea to retain a test bead of epoxy into a plastic bag or small bottle periodically during the job. This will provide verification that the epoxy being injected will cure properly.

On many jobs, the taking of core samples through the crack is required to verify full penetration and cure of the epoxy resin. This is an advisable procedure for the applicator to follow, whether or not the engineer or owner requires it as proof-positive of good workmanship. The cored holes are generally repaired with cementitious or epoxy mortar grout.

Removing the Caps

Following the injection, some owners will require that the epoxy cap be removed from the exposed crack face. This can be accomplished with a right angle grinder if proper dust protection and control steps are taken. If the removal of the cap is not required, leave it in place as it is a labor intensive step.

Special Circumstances

It is possible to successfully inject into wet cracks with limited compromise of bond strength, if certain procedures are followed. If the presence of water, unusual temperature or abnormal substrate (like brick or stone) present themselves on a crack injection project we would encourage you to call the manufacturer to seek additional advice. These instructions are intended to offer a broad overview of the crack injection procedures, and are not intended as a complete manual for all circumstances.

ATC, Adhesives Technology Corp, is a leader in the development of products made specifically for structural concrete repair. ATC products have been approved by over forty State Departments of Transportation and are currently in use by the US military in Iraq. For more information on structural crack injection, concrete anchoring or other concrete products contact ATC's North Eastern distributor, Kelken Construction Systems.

Ken Ginsky
Phone: (732) 721-0249
http://www.kelken.com/kelken-contact-us.html

Information provided by Adhesives Technology Corp.
Article composed by,
 Nick Denroche
VP Marketing, Contractor Power