Crack Injection: When we observe a crack on a concrete slab or beam, we can either patch it with something to close it or we can seal it with a high-strength resin that provides compressive strength and bond strength. For this, engineers prefer epoxy resin because it has strength and good bonding properties.
Most epoxy resin available in the market caters for dry cracks condition as the epoxy resin will not set when it is mixed with water. For wet cracks, either underwater epoxy resin or high-strength polyurethane resin shall be selected for crack injection. In this respect, 2 components of the polyurethane resin are ideal as it will react with the water to form a stiff material with a bonding strength of 1.5 N/mm2. It is important to know that structural polyurethane resin can achieve a compressive strength of 80 MPa and this is equivalent to the strength of an epoxy resin. Upon contact with water, polyurethane resin forms a rigid structure that does not allow air and water to pass through the cracks. When the cracks are sealed and air-tight, corrosion of the steel reinforcement can be prevented.
At the job site, it is not difficult to spot a group of injection nipples or injection packers sticking out along the line of crack to illustrate the repair job is completed by visual inspection. Now the question to ask is whether the resin has penetrated into the cracks as intended by the structural engineers who specified the method of repair. Surprising enough, nobody seems to be interested in asking whether the cracks are sealed properly. The sight of seeing rows of injection nipples or packers basically confirmed that the job was done as intended. So it is basically good showmanship because we don’t normally questioned whether the cracks have been properly sealed with injection resin or not.
For method that uses surface packer or injection nipple where only epoxy adhesive is used to bond the nipple to the concrete, the injection resin could not travel far into the cracks because surface packer or nipple are not designed to handle high injection pressure. Low injection pressure limits the penetration depth of the resin and it is likely to result in incomplete filling of the cracks or even no fill at all if the packers/nipples were not aligned with the crack. Repair specialist prefers this method because it is quick and easy to do since drilling is not required. But it is often more of a showmanship to show the structural engineer that injection has been done to seal the cracks.
3. Resin rebound back at the location of the packer and this indicates a roadblock situation. Therefore, injecting into solid concrete.
4. Injection packers were left on site. Perhaps to show proof of injection by showing the number of packers installed.
With a perfect hole that connects the cracks to a high-pressure piston injection pump, the chances are you will not require to drill as many holes as seen in the picture above. The one with the most number of packers is the likely outcome of an amateur contractor with good showmanship.
2. Injection pressure. The key is to achieve consistent injection pressure during the process of injection.
3. Injection resin mix ratio and setting time. An ultra-fast setting resin requires a plural pump set up and built-in flushing capability.