There are several reasons why concrete cracks, it may be because of shock load the concrete member may have experienced before the proper 28 days aging to get its designed loads, or simply because of degrading as the year passes by. Anyhow, there are techniques that engineers follow to repair concrete cracks. The most common one is by application of concrete epoxy.
Cracks on any concrete members jeopardize its structural durability. That is why builders found a way to repair these cracks at the most economical rather than completely demolish the member. Globally accepted, engineers and consultants use concrete epoxy to repair these stubborn cracks.
Concrete epoxy by definition is a type of resin obtained from the polymerization of epoxides. Having the characteristics of epoxies, these materials are frequently used as coatings and adhesives. Several brands from manufacturers are now available in the market.
Anyhow, these step-by-step guides should provide engineers with an idea of how to repair concrete cracks using concrete epoxy.
Step 1: Define the extent of the concrete cracks
The first thing to do is to mark the cracks, including all hairline cracks with visible paint. This initiative is done by a quality assurance engineer to ensure that no cracks will be left unnoticed. Furthermore, cracks should be determined whether it is a live cracks or not. To determine if the crack is growing, simply put a piece of scrap glass, a thin one, on the crack and glue it with super glue or any approved adhesive materials. Mark a reference point on the crack through the glass and measure it. Wait for several months and check if there are any movements. Any changes would mean that the crack is growing and thus structural intervention is needed.
This is done by simply chiseling the surface of the cracks. Meticulously see to it that any hairline cracks are defined by marking for these to be included in the concrete epoxy injection. Leaving any crack behind would mean air and water seepage that would later become a reason for reinforcing bar rusting, gradually decreasing the strength of the member. Also, unnoticed crack left behind would just propagate another crack jeopardizing the logic of the concrete crack repair.
Step 2: Thoroughly clean the cracks
Once the extent of the crack has been defined, engineers normally then clean the cracks by means of high-powered construction blowers. This is to ensure that chiseled cracks are dust-free to the deepest part of the chiseled area. Any foreign particles added to the concrete epoxy would lose its adhesiveness to the surface. There are other times that quality control engineers pump the cracks with water and then left to dry for 24 hours to truly clean the inside of the cracks.
Step 3: Place the injection ports and seal the cracks
After seeing to it that the cracks are thoroughly cleaned and dust-free, fix the injection ports properly that even slight moving is unlikely to happen. Any advances to the fixed position of the injection ports would mean leakage and destruction. The cracks have to be properly sealed to ensure that no sealer is leaked and every void is filled with the concrete epoxy to attain its main purpose, filling the voids.
Step 4: Inject the breach
Gradually inject the crack via the chosen injection port. This has to be done immediately after the positioning of the injection port. Normally, injection ports are placed at a certain distance to ensure that every pathway of the concrete crack is filled. It is advisable for engineers to ask the supplier or check the brochure to give you an idea of the designed distance.
Injecting breaches is best done with the presence of the supplier representative. They will give you an idea of the best place to place injection ports. They are also trained to see to it that not too much concrete epoxy is injected. Some workers would inject too much epoxy that excess materials or bulging would mean not pleasing aesthetically.
Step 5: Remove the injection port
Again, check the concrete epoxy brochure used to know how many hours it is allowed for the injection port to be removed. Normally, it would take 24 hours to 48 hours for these ports to be removed. Some builders use sandpapers to properly even out any stubborn bulging of these concrete epoxy promoting a better aesthetic of the repaired concrete member. Further, it is advisable to check the dried-up color of the epoxy and compare it with the existing color of the member. Some architects are oozy enough that they wouldn’t like to see the obvious repairing of these concrete cracks.
Quality Engineer Tip:
• I recommend reading the 5 Methods to Avoid Concrete Cracking this will remind you what you need to do.
• You can also read this International Standard from BSI for “Product and System for the Protection and Repair of Concrete” BS EN 1504-8:2016 this is just to ensure the quality of repair complies with international standards.
• Ensure that scaffolding or formworks are properly installed as per approved shop drawing.
There are several manufacturers of concrete epoxy now available in the market. Explore and you will see various product for certain concrete members. Some concretes are too durable but are not paintable at all. Some are less durable but are paintable. Always check and explore what product is best for you.
For best results, it is advisable for the builders to let the supplier have the demo. It is good to know that most suppliers are willing to provide a sample and demo for the construction team to give information on the proper application of their product. Especially for bulk buying, these suppliers are even generous enough to give a humorous discount just to pitch some sales. All you have to do is reach out.
Here is the related British Standard for crack injection:
• BS EN 14068:2003 Determination of water tightness of injected cracks without movement in concrete,
• BS EN 12617-2:2004 Shrinkage of crack injection products based on polymer binder: volumetric shrinkage,
• BS EN 12637-3:2003 Compatibility of injection products. Effect of injection products on elastomers.