Concrete Crack Repair Methods – PDFBAG

Concrete is prone to developing cracks over time due to various factors such as shrinkage, temperature changes, and structural movement. To repair these cracks, there are several methods available, each with its own advantages and limitations. The selection of the appropriate method for a particular crack depends on several factors such as the location and severity of the crack, the cause of the crack, and the expected future loads on the structure.

Concrete Crack Repair Methods

Here is brief introduction of all methods. One popular method of concrete crack repair is epoxy injection, which involves injecting a low-viscosity epoxy resin into the crack to fill and bond the crack surfaces. This method is suitable for cracks that are narrow and actively leaking, and it provides a permanent and strong repair.

Routing and sealing is another method that involves cutting a groove along the length of the crack, cleaning the surface, and filling the groove with a sealant material. This method is suitable for wider and non-structural cracks and can be used to prevent water and other contaminants from entering the crack.

Grouting involves filling the crack with a cementitious or epoxy material to improve the structural integrity of the concrete. This method is suitable for wider and deeper cracks and can also be used for repairing damaged or spalled concrete.

Stitching involves drilling holes on either side of the crack and placing a steel bar or wire in the holes to hold the crack together. This method is suitable for repairing wider and actively moving cracks and can also be used for repairing joints and spalls.

Drilling and plugging involves drilling holes into the crack and inserting metal or plastic ports, which are then filled with an epoxy or cementitious material. This method is suitable for repairing wider and deeper cracks and can also be used for repairing damaged or spalled concrete.

Gravity filling involves pouring a low-viscosity material into the crack and allowing it to flow into all the voids. This method is suitable for narrow and non-structural cracks and can be used to prevent water and other contaminants from entering the crack.

Selecting the appropriate method for concrete crack repair requires careful consideration of several factors, and a combination of methods may be needed for complex or severe cracks. It is always recommended to consult a professional for advice on the most appropriate repair method for your particular situation.

How to Select Suitable Method of Concrete Crack Repair?

To choose an appropriate method for repairing cracks in concrete, it is essential to evaluate the crack’s cause within the structure. Understanding the type of crack that has occurred is also important in determining the most suitable repair method. For instance, if the crack is primarily caused by drying shrinkage, it is likely that the crack will stabilize after a certain period of time. However, if the cracks are due to ongoing foundation settlement issues, repairing the crack will not be effective until the settlement problem is resolved.

The cause of the crack must be identified before selecting a repair method. Different causes may require different solutions. For example, if the crack is due to overloading, the solution might involve reducing the load on the structure. If the crack is due to poor construction practices, repair will involve rectifying the poor workmanship.

It is important to choose the most appropriate repair method to ensure the longevity of the repair. If the repair is not correctly done, the crack may reoccur or worsen. In some cases, it may be necessary to seek the help of a professional engineer to identify the cause of the crack and suggest the best repair method. This can help avoid costly repairs in the future.

Methods of Concrete Crack Repair

1. Epoxy injection

The epoxy injection method is a technique used to repair cracks in various types of concrete structures such as buildings, bridges, dams, and others. The method can effectively repair cracks as narrow as 0.002 inch (0.05 mm). The process involves establishing entry and venting ports along the cracks, sealing the crack on exposed surfaces, and injecting the epoxy under pressure.

However, the success of this technique is limited if the cause of the cracking has not been corrected. If the cause of the cracks cannot be removed, two options are available. One option is to rout and seal the crack, treating it as a joint. The other option is to establish a joint that can accommodate the movement and then inject the crack with suitable material.

This technique is not suitable for actively leaking cracks that cannot be dried out, except for certain moisture-tolerant epoxies. Wet cracks can be injected using moisture-tolerant materials, but contaminants in the cracks, such as silt and water, can reduce the effectiveness of the epoxy to structurally repair the cracks.

It should be noted that using a low-modulus, flexible adhesive in a crack will not allow significant movement of the concrete structure. The effective modulus of elasticity of a flexible adhesive in a crack is almost the same as that of a rigid adhesive, primarily because of the thin layer of material and high lateral restraint imposed by the surrounding concrete.

It requires a high degree of skill to execute epoxy injection satisfactorily, and the application of the technique may be limited by the ambient temperature.

Epoxy injection Procedure

When repairing concrete cracks, the first step is to clean them thoroughly, removing any contaminants such as oil, grease, dirt, or fine particles of concrete that may prevent proper epoxy penetration and bonding. Cleaning can be done by vacuuming, flushing with water, or using specialized cleaning solutions. Once the cracks are clean, surface cracks should be sealed to prevent the epoxy from leaking out before it has gelled. This can be achieved by applying an epoxy, polyester, or other appropriate sealing material to the surface of the crack and allowing it to harden. If a permanent glossy appearance along the crack is not desired, a strippable plastic surface sealer may be applied instead.

Next, entry and venting ports need to be installed. Three methods can be used, including fittings inserted into drilled holes, bonded flush fittings, or an interruption in the seal. The method used depends on the nature of the crack and the specific repair requirements.

After the ports are installed, the epoxy needs to be mixed either by batch or continuous methods. Care must be taken to mix only the amount of adhesive that can be used prior to commencement of gelling of the material. Hydraulic pumps, paint pressure pots, or air-actuated caulking guns may be used to inject the epoxy. The injection process should begin at the lowest elevation for vertical or inclined cracks and from one end of the crack to the other for horizontal cracks.

Once the injected epoxy has cured, the surface seal should be removed by grinding or other means as appropriate. For massive structures, an alternative procedure involves drilling a series of holes that intercept the crack at various locations, usually spaced at 5-ft (1.5-m) intervals. Another method being used is a vacuum or vacuum-assisted method, where the cracked member is entirely enclosed with a bag and liquid adhesive is introduced at the bottom while a vacuum is applied at the top. Epoxies are typically used, but acrylics and polyesters have also proven successful.

2. Routing and Sealing of Cracks

Routing and sealing cracks is a method used for repairing cracks in concrete surfaces without requiring extensive structural repairs. This technique involves widening the crack’s exposed face and then filling and sealing it with a suitable joint sealant, as shown in Figure 1. This approach is relatively simple compared to the procedures needed for epoxy injection and is most commonly used for flat horizontal surfaces such as pavements and floors. However, it is also suitable for vertical surfaces when a non-sag sealant is used and curved surfaces such as pipes, piles, and poles.

Routing and sealing is an effective way to treat both small and large cracks in concrete surfaces. It is commonly used for waterproofing by sealing cracks where water accumulates or where there is hydrostatic pressure. This treatment prevents moisture from reaching the reinforcing steel or passing through the concrete, which could cause surface stains or other issues. The sealants used can be made of various materials, including epoxies, urethanes, silicones, polysulfides, asphaltic materials, or polymer mortars. However, cement grouts should be avoided due to their tendency to crack.

To perform routing and sealing, a groove is prepared at the surface, typically ranging from 1/4 to 1 inch (6 to 25 mm) deep. This groove can be created using a concrete saw, hand tools, or pneumatic tools. The groove is then cleaned by air blasting, sandblasting, or waterblasting, and dried. A sealant is then placed into the dry groove and allowed to cure. To prevent stress concentration on the bottom of the groove, a bond breaker may be provided, as shown in Figure 2. The sealant used should be able to withstand cyclic deformations and should not be brittle. For floors, it should also be sufficiently rigid to support expected traffic.

In order to prevent bonding of the sealant, a polyethylene strip or tape is commonly used as a bond breaker. It is important to pay close attention to the joint detailing process to ensure that the width to depth aspect ratio is suitable for the anticipated movement, as recommended by the American Concrete Institute’s publication 504R. By following these guidelines, the joint will be able to accommodate movement without compromising the integrity of the sealant. Therefore, it is crucial to take careful measures during the joint detailing process to ensure optimal performance of the sealant and joint.

3. Concrete Crack Repair by Stitching

Stitching is a process used to restore tensile strength across major cracks. This process involves drilling holes on both sides of the crack and inserting U-shaped metal units with short legs, which are also known as staples or stitching dogs. These metal units span the crack and help to reinforce the structure.

To carry out the stitching process, the first step is to drill holes on both sides of the crack. The holes are then cleaned, and the legs of the staples are anchored in the holes using either a non-shrink grout or an epoxy resin-based bonding system. This helps to secure the staples in place and reinforce the structure.

Stitching is particularly useful when tensile strength needs to be reestablished across major cracks. The process is effective in strengthening the structure and preventing further damage. By inserting the metal staples and anchoring them securely, the structure becomes more stable and can better withstand external forces. Overall, stitching is a reliable and efficient method for repairing and reinforcing structures with major cracks.

4. Additional Reinforcement for Crack Repair

Conventional Reinforcement

Reinforced concrete bridge girders that have been cracked can be repaired using a technique that involves inserting reinforcing bars and bonding them in place with epoxy. This method has been proven to be successful in repairing such girders. To begin with, the crack is sealed and then holes are drilled into it. These holes are drilled so that they intersect the crack plane at approximately 90 degrees, as shown in Figure 4. After the drilling is completed, the hole and crack are filled with injected epoxy.

In order to reinforce the repair, a reinforcing bar is placed into the drilled hole. Typically, No. 4 or 5 (10 M or 15 M) bars are used, and they should extend at least 18 inches (0.5 m) on each side of the crack. The spacing of the reinforcing bars can be adjusted to suit the needs of the repair. The bars can be placed in any pattern that is deemed necessary based on the design criteria and the location of the in-place reinforcement.

Overall, the repair process for cracked reinforced concrete bridge girders involves sealing the crack, drilling holes into the crack plane at a 90-degree angle, filling the hole and crack with injected epoxy, and placing reinforcing bars into the drilled holes. This method has been effective in repairing such girders and reinforcing them for future use.

Fig.4: Reinforcement bar orientation for crack repair

Prestressing steel

Post-tensioning is a popular technique used to strengthen a significant part of a member or to close existing cracks. It involves the use of pre-stressing strands or bars to apply a compressive force to the member. This technique is preferred because it can effectively address the issue of cracks and increase the overall strength of the structure.

However, it is essential to provide adequate anchorage for the prestressing steel to ensure its effectiveness. Without proper anchorage, the prestressing steel will not be able to provide the necessary compressive force, rendering the technique useless. Furthermore, it is crucial to exercise caution during the process to prevent the problem from simply relocating to another area of the structure.

In summary, post-tensioning is a desirable solution for strengthening a significant portion of a member or closing existing cracks in a structure. It involves using pre-stressing strands or bars to apply compressive force to the member. Adequate anchorage is crucial, and it is important to exercise caution during the process to prevent the problem from simply relocating to another area of the structure.

5. Drilling and Plugging Method

“Drilling and plugging a crack” is a technique used to repair cracks in structures. The process involves drilling a hole along the length of the crack and then filling it with grout, which is a type of cement mixture. The purpose of this technique is to create a “key” that will help to hold the structure together and prevent further cracking.

The first step in the process is to identify the location of the crack and determine its length. Once this has been done, a series of holes are drilled along the length of the crack, typically at regular intervals. These holes are then filled with grout, which is injected under pressure to ensure that it fills the crack completely.

As the grout sets, it forms a solid mass that fills the void created by the crack. This effectively creates a “key” that helps to hold the structure together and prevents further cracking from occurring. The process can be used to repair cracks in a wide range of structures, including concrete and masonry walls, bridges, and other types of infrastructure.

Overall, drilling and plugging a crack is a reliable and effective technique for repairing structural damage caused by cracking. It involves drilling holes along the length of the crack and filling them with grout to create a key that helps to hold the structure together and prevent further damage.

This particular approach for repairing cracks is suitable only for cases where the cracks follow relatively straight lines and can be accessed from one end. Its primary application is in fixing vertical cracks that occur in retaining walls. To initiate the repair process, a hole is drilled into the wall, typically measuring 2 to 3 inches (50 to 75 mm) in diameter, and is centered on the crack to be addressed. By doing so, the grout key helps to prevent the adjacent sections of concrete from moving transversely. Moreover, the grout key also helps to minimize heavy leakage through the crack and prevent the loss of soil from behind the wall, especially in cases where the wall is leaking.

When water-tightness is a critical requirement, and there is no need for structural load transfer, it is advisable to fill the drilled hole with a resilient material of low modulus instead of grout. However, if the keying effect is crucial, then a second hole can be created and filled with the resilient material while the first hole is filled with grout. This approach helps to achieve the desired keying effect while also maintaining water-tightness. Overall, this technique is particularly useful in addressing vertical cracks in retaining walls and can help to prevent further damage and potential collapse.

6. Gravity Filling Method

Cracks in concrete surfaces with widths ranging from 0.001 to 0.08 inches (0.03 to 2 millimeters) can be sealed using low viscosity monomers and resins through the process of gravity filling. High-molecular-weight methacrylates, urethanes, and some low viscosity epoxies have been found to be effective in this regard. The success of the sealing process is dependent on the viscosity of the material used, with lower viscosity materials being able to fill finer cracks.

To prepare the surface for sealing, it is recommended to clean it through air blasting and/or water blasting. If the surface is wet, it is important to allow sufficient drying time of several days to ensure optimal crack filling. Water blasting followed by drying time can be a useful technique to clean and prepare the cracks. To evaluate the effectiveness of the crack filling, cores taken at the cracks can be analyzed. The depth of penetration of the sealant can be measured, and shear or tension tests can be performed. It is important to apply the load parallel to the repaired cracks, as long as reinforcing steel is not present in the core in or near the failure area. In some cases, the failure crack may occur outside the repaired crack for certain types of polymers.

7. Crack Repair Grouting Method

Portland cement grouting

When it comes to repairing wide cracks, especially in gravity dams and thick concrete walls, the use of Portland cement grout is an effective method for stopping water leaks. However, it is important to note that this technique does not provide a structural bond for the cracked sections.

The process of repairing the crack using Portland cement grout involves several steps. Firstly, the concrete around the crack must be cleaned thoroughly. Built-up seats, also known as grout nipples, are then installed at intervals on either side of the crack. These seats help to create a pressure-tight connection with the injection apparatus. The crack is then sealed using a cement paint, sealant, or grout. Once the seal is in place, the crack is flushed to clean it and test the seal before the entire area is grouted.

Depending on the width of the crack, the grout mixture may contain cement and water, or cement plus sand and water. However, it is important to keep the water-cement ratio as low as possible to maximize strength and minimize shrinkage. Water reducers or other admixtures may also be added to improve the properties of the grout.

For small volumes of grout, a manual injection gun can be used, while a pump should be used for larger volumes. Once the crack is filled, the pressure must be maintained for several minutes to ensure good penetration of the grout.

In summary, using Portland cement grout to repair wide cracks can effectively stop water leaks. However, it is important to note that this method does not provide structural bonding for cracked sections. The repair process involves cleaning the concrete around the crack, installing built-up seats, sealing the crack, flushing and testing the seal, and grouting the area using a suitable mixture. The water-cement ratio should be kept low, and pressure should be maintained for several minutes after filling the crack to ensure proper penetration of the grout.

8. Dry packing

Dry packing is a technique that involves placing a low water content mortar by hand and then compacting it through tamping or ramming to achieve a tight and durable patch. This process creates intimate contact between the new and existing concrete, making it ideal for filling narrow slots in dormant cracks.

However, it is not recommended to use dry packing for active cracks. Before repairing a crack with dry packing, the surface adjacent to it should be widened to a slot that is 1 inch (25 mm) wide and 1 inch (25 mm) deep. The slot should also be undercut to ensure that the base width is slightly greater than the surface width.

To minimize shrinkage in the final product, the mortar mixture should stand for half an hour after mixing, and then remixed prior to use. The mortar should be placed in layers that are about 3/8 inch (10 mm) thick, and each layer should be thoroughly compacted using a blunt stick or hammer. Additionally, each underlying layer should be scratched to facilitate bonding with the next layer.

To ensure proper curing, the repair should be cured using either water or a curing compound. One way to moist cure is by supporting a strip of folded wet burlap along the length of the crack. Overall, dry packing is a useful technique for repairing cracks as long as it is used correctly and with the appropriate materials.

8. Overlay and Surface Treatments of Cracks

Structural slabs and pavements with fine surface cracks can be repaired through two methods: bonded overlay or surface treatment, as long as there is no significant movement expected to occur across the cracks in the future. In cases where the cracks are not severe enough to penetrate the slab completely, either a bonded overlay or surface treatment can be used to repair them. However, if there is no intention to repair the slab and only to cover it up, then an unbonded overlay may be used.

If the cracks were caused by a one-time occurrence, and there is no significant movement expected across the cracks in the future, then an overlay or surface treatment may be appropriate for repairing them. However, it is essential to note that unbonded overlays are not suitable for repairing slabs; they only provide coverage. Ultimately, the choice of repair method will depend on the extent and nature of the damage and the intended use of the slab or pavement.

9. Surface Treatments

Low solids and low-viscosity resin-based systems are commonly utilized for sealing concrete surfaces, including those with very fine cracks. These types of materials are best suited for surfaces that do not experience significant wear and tear. For instance, they can effectively coat bridge decks, parking structure slabs, and other interior slabs after treating any cracks by injecting them with epoxy or by routing and sealing them.

There are various materials that can be used for this purpose, such as urethanes, epoxies, polyesters, and acrylics. The thickness of the coating can range from 0.04 to 2.0 inches (1 to 50 mm) depending on the material and the intended purpose of the treatment. In order to improve traction, skid-resistant aggregates are often added to the material or broadcasted onto the surface.

Overall, low solids and low-viscosity resin-based systems are effective solutions for sealing concrete surfaces and treating cracks. However, the appropriate material and thickness of the coating should be carefully considered based on the specific application and expected wear and tear.

Overlays

When slabs containing dormant cracks need to be repaired, one possible solution is to apply an overlay. This overlay can take the form of either a polymer modified Portland cement mortar or concrete, or a silica fume concrete. In the case of slabs with working cracks, it is possible to overlay them if joints are placed in the overlay directly over the working cracks. This approach has been successfully used in highway bridge applications, with overlay thicknesses as low as 1-1/4 in. (30 mm).

In order to make a suitable polymer overlay, it is important to use the right type of polymer. Polymers such as styrene butadiene or acrylic latexes can be used for this purpose. When making the overlay, it is important to ensure that the resin solids make up at least 15 percent by weight of the Portland cement. In fact, 20 percent is usually the optimum amount.

Overall, applying an overlay can be an effective way to repair slabs with cracks. By choosing the right materials and techniques, it is possible to ensure that the overlay is strong and long-lasting.

FAQs Concrete Crack Repair Methods

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