The focus of this text is on the various techniques employed in the repair of concrete structures submerged underwater. The methods and procedures involved in repairing these structures will be explored in detail.
Concrete structures that have been submerged underwater for extended periods of time may require repair due to damage caused by exposure to the elements. Several approaches are used to fix these structures, and each has its own set of procedures.
The aim of this text is to outline the specific procedures used for repairing underwater concrete structures. These methods are diverse and must be tailored to the unique characteristics of each structure.
By the end of this discussion, readers should have a better understanding of the various techniques used in underwater concrete repair and the necessary steps involved in implementing them.
Repair of Underwater Concrete Structures – Methods and Procedure
Underwater concrete structures can be susceptible to damage over time due to factors such as water pressure, erosion, and corrosion. To repair such structures, there are several methods available, each with its own advantages and disadvantages.
Surface spalling repair is a common method used to repair minor damages to underwater concrete structures. This involves removing the damaged concrete from the surface and replacing it with a new layer of concrete. This method is cost-effective and can be completed relatively quickly, making it an ideal choice for minor damages.
For larger scale repairs of underwater structural concrete, preplaced aggregate concrete is a suitable method. In this technique, the damaged area is filled with pre-placed aggregate concrete. This method is beneficial as it does not require heavy equipment and can be performed using standard diving equipment.
Another method for restoring the underwater concrete structure is injection technique. This method involves injecting a material, typically a cement-based mixture, into the damaged area using a high-pressure pump. This technique is particularly useful for repairing cracks and voids in the concrete, as it can fill these areas completely.
Guniting or shotcrete is another method used to repair underwater concrete structures. In this technique, a dry mix of cement and aggregate is sprayed onto the damaged area using a high-pressure hose. This method is useful for repairing larger areas of damage, as it can be performed relatively quickly and provides good adhesion to the existing concrete.
Finally, steel sleeve repairing technique is also an option for repairing underwater concrete structures. This method involves placing a steel sleeve around the damaged area and filling it with concrete. The steel sleeve provides additional support to the damaged area and prevents further damage from occurring. This technique is useful for repairing larger areas of damage that require additional support.
Surface Spalling Repair of Underwater Concrete Structures
Underwater structures are susceptible to accidental damages that can cause the spalling off of their concrete covers. To prevent corrosion of the reinforcement in the future, it is essential to replace and repair the damaged cover. Even slightly deteriorated regions can rapidly turn into severe and dangerous damages, particularly in splash zones. Therefore, it is crucial to clear the deteriorated area of the underwater structure from both marine growth and loose concrete before beginning any repair procedures.
Depending on the extent of the damage, the boundary of the spalled area should be saw-cut to a depth of 1.2-2 cm. For damaged regions in splash zones, cementitious mortar is the preferred option. In the case of small damaged areas, water-tolerant epoxy mortar may be employed. However, for large repaired areas, formworks may be used to hold the repairing material in place. It is important to note that this could delay enhancement work and prevent the use of epoxy coat, as it can produce a smooth surface that results in a weak bond.
Figure-1 and Figure-2 illustrate two different types of surface repairing formwork that can be used in the repairing procedures. By following these guidelines and procedures, the integrity of underwater structures can be maintained, and the risk of future damages can be reduced.
The procedure of Surface Spalling Repair of Underwater Concrete
The surface spalling repair technique involves a series of basic procedures that are essential for its effective implementation. Firstly, the damaged region must be thoroughly cleaned by flushing it with fresh water to remove any debris or loose particles that could impede the repair process.
Next, a bonding coat should be applied to the cleaned surface to enhance the adhesion of the repair mortar to the substrate. Once the bonding coat is in place, the repair mortar can be applied before it sets, ensuring that it adheres properly to the surface.
After the repair mortar is applied, a curing membrane is placed over it to prevent moisture loss and maintain the optimal curing conditions. This step is crucial for ensuring that the repair mortar sets properly and achieves its maximum strength.
Finally, the repaired area must be protected against wave action until it has hardened adequately. This step ensures that the repaired surface is not damaged by the impact of waves or other external factors that could compromise its integrity. By following these basic procedures, the surface spalling repair technique can effectively restore damaged surfaces and extend their useful life.
Fig.1: Formwork for Placement by Pumping
Fig.2: Bird’s-Mouth Type Formwork for Surface Spalling Repair
Large Scale Repair of Underwater Concrete Structures
There is a technique that is effective in repairing damages caused by structural overloading, fire, ship impact, or reinforcement corrosion, especially in the splash zone. When dealing with large areas that require restoration, the choice of repair method and material is crucial. This is because there is a risk of shrinkage or bleeding that could create a leakage path at the interface between the parent concrete and the repair material. Additionally, when repairing materials that are thick, thermal cracking may occur due to the rise in temperature, even though the surrounding water helps to reduce the temperature rise. It is also common to repair reinforcement due to distortion and significant corrosion.
Procedure of Large Scale Repair of Underwater Concrete
Large-scale repair procedures typically involve several steps to ensure that the damaged region is effectively repaired. First, the area in need of repair must be carefully prepared to remove any debris or loose material that could interfere with the repair process.
The reinforcement in the area must also be adequately cleaned to ensure that it is free of any contaminants that could weaken the repair. Once the preparation is complete, the type of formwork required for the placement method of the repairing material must be determined.
To reduce the risk of concrete contamination with salts, it is essential to flush the formwork with fresh concrete a short period before pouring the repair concrete. This helps to eliminate any potential contaminants that could affect the quality of the repair.
When it comes to placing the repair material, pumping is the most commonly used method. It is essential to begin pumping at the bottom of the formwork to push any water out from the bottom and ensure that the repair material is placed correctly. By following these steps, large-scale repair procedures can be carried out effectively, ensuring that the repaired structure is safe and structurally sound.
Preplaced Aggregate Concrete
To repair a damaged area, the first step is to install formwork at the intended location. Then, a well-graded aggregate is placed and compacted inside the formwork. It’s important to use freshwater to clean the aggregate before injecting the grout.
Once the aggregate is compacted, the appropriate grout is injected into the base of the aggregate. The grout displaces water and voids, which are expelled out of the aggregate. To prevent leaking, the formwork must be grout-proof and have proper venting at the top to allow escaping voids and air.
It’s crucial to fill the formwork completely with aggregate up to the top of the damaged region. If the grout is injected without enough aggregate present, it will shrink and cracks will form. To avoid washing out the grout, it’s recommended not to apply vibration during injection.
Injection Technique for Restoring Underwater Concrete Structures
Repairing cracks and voids in concrete structures underwater can be achieved through the injection of cementitious grout or resin, similar to the process used for dry structures. The selection of the appropriate material depends on the size of the crack or void and the possibility of any future movement of the structure. Epoxy resin is suitable for cracks with a width of 0.1 mm or less, while cement grout is more appropriate for larger cracks with a width of several millimeters. For cracks with a width smaller than 0.1 mm, injection may not be necessary.
The pressure and duration of pressure applied before the repair material solidifies are also important considerations in the injection process. Two injection methods can be employed: pressure injection and gravity feed. However, if there is evidence of corrosion, it may be necessary to break the concrete down to the reinforcement, and complete repairs should be suggested instead of using the injection method.
The procedures for injection techniques are
To prepare the concrete surface for repair along the crack length, it is necessary to first fix inspection nipples at specific intervals. These nipples will allow for easy access to the crack during the repair process. Once the nipples are in place, the crack surface should be sealed along its entire length to ensure that the repair material can properly penetrate the crack.
Before beginning the injection process, it is important to remove any contamination from the crack surface using fresh water. This will ensure that the injection path is clear and unobstructed.
To inject the epoxy resin or cement grout into the crack, it should be done through the nipples installed at one end of the crack. This will allow the repair material to flow through the entire length of the crack and properly fill any voids or gaps that may exist. It is important to carefully follow the manufacturer’s instructions for mixing and injecting the repair material to ensure the best possible outcome.
Guniting or Shotcrete Method to Repair Underwater Concrete Structures
Guniting is a commonly used technique when large surface areas, columns, or beams require repair or reinforcement. Typically, the dry process is used in which a dry mix is conveyed through a hose, and water is added at the nozzle. However, it’s important to note that this method is not suitable for underwater repairs. Nevertheless, in areas with splashing or tidal zones, it can still be used if rapid setting additives are incorporated.
The proficiency of the nozzle operator is a key factor in the success of guniting. This includes adjusting water addition, pressure, and thickness uniformity to ensure that the repair is applied evenly and to the desired thickness. While a maximum thickness of fifty millimeters is recommended, thicker layers may be required and can be achieved through the use of a second layer.
In summary, guniting is a popular technique for repairing or reinforcing large surfaces, columns, or beams. The dry process, where dry mix and water are combined at the nozzle, is typically used. While guniting is not appropriate for underwater repairs, it can be used in areas with splashing or tidal zones if rapid setting additives are used. The success of the repair largely depends on the skill and experience of the nozzle operator and the ability to apply the repair evenly and to the desired thickness. Finally, a maximum thickness of fifty millimeters is recommended, although a second layer can be applied for thicker repairs.
Steel Sleeve Repairing Technique of Underwater Concrete
The described method involves using a steel sleeve to surround a pile or column. The space between the sleeve and the pile or column is then filled with mortar or concrete. This technique allows for the sleeve to accommodate additional reinforcement corrosion. To ensure structural integrity, the sleeve should extend beyond the top and bottom of the damaged length of the pile and be able to withstand the force of the pile, in case the bars become ineffective due to corrosion. Figure 3 depicts a common configuration of steel sleeves used in this method.
Fig.3: Arrangement of Steel Sleeve Repair
A steel sleeve repair technique procedure is as follows
To prepare the damaged pile that has loose concrete and marine growth, the first step is to clamp a temporary support or sealing ring around the pile below the damaged area. This will ensure that the damaged section does not collapse during the repair process. The support or ring should be placed firmly to prevent any movement during the repair work.
Once the support or ring is in place, the damaged area needs to be cleaned and prepared for the repair process. This can involve removing loose concrete and marine growth to expose the underlying surface. This will ensure that the repair material will adhere properly to the surface of the pile.
After the preparation is complete, a steel sleeve should be employed to provide a long-term solution for the damaged pile. The steel sleeve should be made up of two semi-circular sections that can be clamped together around the damaged area. Once the steel sleeve is in place, grout or cement should be pumped into the bottom of the sleeve. This will ensure that the steel sleeve is secured in place and that the damaged area is filled with a strong material.
Finally, the temporary support or sealing ring can be removed, and the steel sleeve should be treated with corrosion protection to ensure that it will last for a long time. This may involve applying a protective coating or wrapping the sleeve in a protective material to prevent corrosion and ensure that the repaired area remains strong and secure.