Concrete is a common material used in construction due to its strength and durability. However, over time, it can develop cracks which can compromise its integrity. Dormant cracks are a type of crack in concrete that have occurred but do not propagate or extend any further, thus becoming dormant.
There are several methods for repairing dormant cracks in concrete, and four of these methods are commonly used. The first method is sealing, which involves filling the crack with a sealant to prevent water or other contaminants from entering the crack and potentially causing further damage.
The second method is routing and sealing, which is similar to sealing but involves first widening the crack using a router before filling it with a sealant. This method is often used for wider cracks or those with irregular shapes.
The third method is bond breaking, which involves creating a void around the crack by drilling holes on either side of the crack and then filling the void with a flexible material. This method allows for movement of the concrete without further cracking.
The fourth and final method is epoxy injection, which involves injecting an epoxy resin into the crack to fill it and provide additional strength to the surrounding concrete. This method is often used for cracks that are actively leaking or for those that require additional reinforcement.
Overall, each of these methods can be effective for repairing dormant cracks in concrete, and the choice of method will depend on the specific circumstances of the crack and the needs of the structure.
Repair of Dormant Cracks in Concrete
Following are the Methods of Repair for Dormant Cracks in Concrete:
Sealing of Cracks
Sealing cracks can serve as a sufficient repair method when there is no need for structural repair. In such cases, cracks that are isolated and extend partially or completely through the concrete section can be sealed at the concrete surfaces. To do this, a slot with a width of approximately 25mm should be saw cut along the center of the crack to a depth of up to 10mm. The concrete between the two saw cut edges should then be chiseled out, and the base should be undercut beyond the 10mm depth to a depth of around 20mm, so that the base width is slightly larger than the surface width.
After the slot is thoroughly cleaned, it should be soaked with water for 10 hours and allowed to surface dry. Then, an approximate latex bonding compound should be applied as a bond coat/primer coat. Once the primer becomes tacky, a high-strength, polymer-modified cementitious mortar should be filled in the slot, properly tamped, and finished at the surface. As soon as the surface becomes touch dry, a curing compound should be applied.
Wet curing should be carried out for 7 days by covering the slot with wet Hessian and a polythene sheet. By following these steps, cracks can be effectively sealed as a standalone repair method.
Routing and Sealing of Cracks
To prepare a crack for repair, one option is to create a V-groove along the surface of the crack. The V-groove should range in depth from 6 to 25mm and have a minimum opening of 6mm at the surface. This preparation method is shown in Figure 1.
Creating a V-groove can be an effective way to prepare a crack for repair. The groove helps to create a stronger bond between the repair material and the existing structure, improving the overall durability of the repair. The depth of the groove should be carefully chosen based on the severity of the crack and the type of repair material being used. It is important to ensure that the minimum opening at the surface is met in order to provide adequate space for the repair material to be applied.
Overall, preparing a crack for repair is an important step in ensuring the long-term integrity of a structure. By creating a V-groove along the surface of the crack, engineers and repair specialists can ensure that the repair material will bond strongly with the existing structure, leading to a more effective and durable repair.
Fig: Repair of crack by routing and sealing
When it comes to creating grooves in a surface, there are a few different tools that can be used, including concrete saws, hand tools, or pneumatic tools. Once the groove has been created, it needs to be thoroughly cleaned. This can be accomplished through a variety of methods, such as air blasting, sand blasting, or water blasting. Once the groove is clean and dry, a sealant can be applied.
There are a number of different materials that can be used for sealants, including epoxies, urethanes, silicones, Polysulphide, asphaltic materials, or polymer mortars. These materials each have their own unique properties and can be selected based on the specific needs of the project.
To ensure that the sealant performs properly, it is important to provide a bond breaker at the bottom of the groove. This allows the sealant to change shape without creating a concentration of stress on the bottom of the groove. Typically, a polyethylene strip or tape is used as the bond breaker, as it will not bond to the sealant. Overall, by following these steps and selecting the appropriate materials, a strong and durable groove can be created.
Bond Breaking Method
In some instances, strip coating or over bonding is utilized either alone or alongside sealing techniques. The process involves cleaning or sandblasting an area approximately 25 to 75mm on each side of the crack and then applying a coating, typically urethane, in a band measuring 1 to 2mm in thickness over the crack. A bond breaker may be employed over the crack or over a previously sealed crack. Over banding may be applied to cracks that are subject to minimal movement, but if significant movement is expected, sealing should be used together with over banding to ensure that the repair is waterproof.
Fig: Effect of bond breaker
Epoxy Injection Method
In the field of construction, it is possible to successfully bond very narrow cracks, measuring as little as 0.3mm, by injecting epoxy into them. However, it is important to note that unless the underlying cause of the crack has been addressed, it is likely to reappear in the same location. If the cause of the crack cannot be removed, and the crack is not affecting the structural integrity of the building or bridge, there are two potential solutions. One approach is to seal the crack with a flexible sealant, treating it as a joint. Alternatively, a joint can be established that can accommodate movement, and then the crack can be filled with epoxy.
It is worth noting that this technique is not applicable in cases where the crack is actively leaking and cannot be dried out, except in cases where moisture-tolerant epoxies are used. It is also important to keep in mind that the process of epoxy injection requires a high level of skill to execute satisfactorily. Finally, it is worth noting that the ambient temperature can limit the applicability of this technique.