Post-concreting defects refer to the defects that are observed in structures after the removal of formwork. These defects may be caused by various factors such as poor workmanship, improper curing, insufficient compaction, and inadequate mixing of concrete.
The repair of post-concreting defects is necessary to ensure the structural integrity of the concrete. The repair process involves the use of suitable materials, equipment, and methods. The choice of materials and equipment depends on the nature and extent of the defects.
In general, the repair materials used for post-concreting defects include cementitious and epoxy-based materials. Cementitious materials are preferred for minor defects while epoxy-based materials are used for major defects. The equipment used for repair includes hand tools such as chisels, hammers, and grinders, as well as power tools such as drills and saws.
The methods of repair for post-concreting defects depend on the type of defect. Common repair methods include patching, grouting, and injection. Patching involves the application of a repair material to the surface of the defect. Grouting involves the filling of voids with a cementitious or epoxy-based material. Injection involves the injection of a repair material into the void using pressure.
In conclusion, the repair of post-concreting defects is a critical aspect of ensuring the longevity and durability of concrete structures. Proper selection of materials, equipment, and repair methods is essential to achieve effective repairs.
Repair of Post Concreting Defects in Structures
Expediency is a crucial element of a successful repair. The longer a repair is delayed, the more extensive the work required to fix the issue becomes. Additionally, as time passes, the repair is less likely to blend in seamlessly with the original condition, resulting in a less satisfactory outcome. Therefore, prompt attention and action are vital for achieving a successful repair.
When repairing concrete, it is crucial to ensure that the surface is clean and free from any dirt, dust, or debris. This is because the presence of contaminants can hinder the bonding process between the repair concrete and the parent concrete. Therefore, prior to repairing, thorough cleaning of the concrete surface is essential to ensure proper adhesion and durability of the repair. It is important to carefully remove any dirt, dust, or other particles that may be present on the surface, using appropriate cleaning methods such as brushing, vacuuming, or pressure washing. By maintaining cleanliness during the repair process, the repair concrete can form a strong bond with the parent concrete, ensuring a successful and long-lasting repair.
The correct technique and tools are crucial when it comes to repairing damaged concrete. Using the right approach and appropriate tools is essential to ensure that the repairs are done effectively and will result in a durable and long-lasting solution. Without proper technique and tools, the repairs may be ineffective, leading to further damage or the need for additional repairs in the future. Therefore, it is imperative to use the correct technique and tools when repairing damaged concrete to ensure the best possible outcome.
The repair material utilized must possess the same level of durability as the original concrete in order to effectively restore the structure. It is imperative that the repair material exhibits comparable strength and longevity as the parent concrete to ensure a long-lasting and reliable repair. The durability of the repair material is of utmost importance to ensure that the restored structure can withstand environmental factors, wear and tear, and other stresses over an extended period of time. Therefore, the chosen repair material must meet or exceed the durability characteristics of the parent concrete to ensure a successful and resilient repair.
It is crucial to conduct repairs on the concrete while it is still in its early stages of curing, as this ensures that the repaired areas will match the characteristics of the original concrete. Prior to repairing, all surfaces to be worked on must be thoroughly cleaned and cleared of loose dirt or dust, to avoid bonding the repair to particles of debris. Those assigned to carry out the repairs should be properly trained in the specific tasks, as repairing concrete requires a higher level of skill compared to initial concrete placement.
Materials for Repairing Post Concrete Defects:
Prior to commencing the repair, it is essential for the operative to ensure that they have all the required materials and equipment readily available. The typical materials utilized for patch repairs include:
Repairs to concrete structures often require the use of a high concentration of cement, which can result in the finished repair appearing darker than the surrounding parent concrete. However, the use of white Portland cement can help to lighten the color of the repair. It is also important to use the same type of aggregate and sand that was used in the original concrete mix, along with limestone fines, which can also contribute to a lighter color in the repaired area.
In addition to cement and aggregates, a gauging liquid is typically used in the repair process. This liquid is usually water mixed with a polymeric material such as styrene butadiene rubber (SBR), polyvinyl acetate (PVA), or an acrylic material. These additives improve the cohesion and adhesion of the repair to the parent concrete, and also enhance the physical properties of the hardened concrete, such as imperviousness and elasticity.
When repairing cracks, the same materials mentioned above can be used, but in some cases, an epoxy or polyester resin may be required, depending on the width of the crack. These resins can provide additional strength and durability to the repaired area. Overall, the selection of materials for concrete repairs depends on various factors such as the type of repair, the desired appearance, and the performance requirements of the repaired structure.
Equipment for repairs of concrete:
The figure provided depicts the typical equipment needed for concrete repair projects. These essential tools and machinery are necessary to effectively carry out repairs on concrete structures. From the image, it can be observed that a range of equipment is required to handle various aspects of the repair process. These may include tools for surface preparation such as grinders, shot blasters, and scarifiers, which are used to remove damaged or deteriorated concrete from the surface to create a clean and sound substrate for repair materials to adhere to. Additionally, equipment for mixing and applying repair materials, such as concrete mixers, pumps, and sprayers, are necessary to ensure proper installation of repair materials. Other equipment such as hand tools, power tools, and safety gear are also shown in the figure, which are essential for carrying out concrete repairs safely and efficiently. Overall, the image provides a visual representation of the general equipment needed for concrete repairs, highlighting the diverse range of tools and machinery required for different stages of the repair process.
If the extent of the repair is significant, it may require the use of formwork, formwork ties or clamps, and string-backs. These tools are used to create temporary molds that hold the concrete in place while it cures. Additionally, plastic sheeting and tape may be needed to cover the repaired area and ensure proper curing. Having these materials available is essential for effective concrete repairs.
Repairing of Honeycombed Concrete:
Repairing honeycombed concrete involves a common technique used for repairing defects, which is to replace the mortar loss near the surface. The process includes several steps. Firstly, using a hammer and chisel, the honeycombed concrete is removed until all the damaged concrete has been cleared. The area is then brushed out to eliminate any dust and debris.
To prepare the replacement concrete, a mixture of cement and limestone fines in a 1:2 combination is used. The cement should consist of an equal mixture of Portland and white cement. Gauging liquid can contain equal amounts of water and polymer, although water alone may suffice for low maturity repairs. The gauging liquid should be added so that the mixture is just moist, and a low slump mix is particularly necessary on vertical surfaces to prevent it from slumping out of position.
The replacement concrete is then placed into the cavity using a trowel. As the repair is small, using a vibrator is not practical, and a rod is used to compact the concrete. The concrete is then smoothed again with the trowel. Finally, the concrete repair is cured by placing plastic sheeting over it and securing it with adhesive tape.
Structural repairs post concreting:
If the honeycombing in concrete is severe or passes through a section, it may be necessary to remove the affected concrete and recast the entire section. Prior to starting this repair process, the column or section above the repair area will need to be supported with appropriate propping to ensure stability. The damaged area can then be broken out, which may require the use of tools such as a pneumatic hammer, as shown in the figure below.
After removing the honeycombed concrete and cleaning the area of dust, the next step is to set up the formwork. The formwork will require a specific hole to be cut into it, often referred to as a “letterbox” or “bird’s mouth.” This hole allows for the concrete to be poured into the formwork while it is still in place.
The concrete mix used for the repair can be identical to the mix used in the original pour. It can be poured through the opening and compacted using a small vibrating poker. Additional external vibration may also be required for proper consolidation. It is important to ensure that the entire void is filled when placing the final layer of concrete. The formwork should be kept in place for 24 hours before being removed to allow for proper curing.
Repair of blow holes in concrete structure:
The “Bagging in” technique is a method used to fix excessive blow holes on the surface of concrete. It involves using a hessian pad to rub a cement paste into the holes, without the need for additional vibration or compaction. The repair mix typically consists of a 1:4 ratio of cement to fine grade sand, often using silver sand, along with enough water to create a very stiff paste that holds together when squeezed, without allowing any water to escape. For best results, the treatment should be performed as soon as the formwork is removed, ideally the day after casting. To further enhance the effectiveness of the repair, a carborundum stone is used to scour the surface and expose any other blow holes near the surface. This process also reveals unhydrated cement particles that can bond with the repair work, improving its overall performance.
A hessian pad is a type of pad made from hessian fabric that is filled with a mixture, likely a cement mixture. This pad is used to rub over a concrete surface in a circular motion, with overlapping motions, in order to fill any holes or gaps in the concrete and coat the surface with a fine cement paste. This process helps to improve the overall appearance and smoothness of the concrete surface.
Repair of cracks in post concrete structures:
Reporting cracks to the relevant supervising authority is a necessary step. It’s important to note that some degree of cracking is normal in concrete structures and may not require immediate attention, depending on their prevalence. However, cracks can also be indicative of underlying issues that need to be addressed. Therefore, it’s essential to report any cracks observed to the appropriate authority for evaluation and appropriate action.
The primary purpose of concrete in the cover zone is to safeguard the steel reinforcement from corrosion. In cases where cracks occur in floor slabs, they can typically be filled with a cement paste, especially if the slab is intended to have a surface topping that will conceal the crack and provide additional protection. However, cracks in walls or other areas where this approach is not feasible require alternative repair methods. The first step is to analyze the cracks to determine if they are live (i.e., likely to grow over time) or not. Live cracks necessitate the formation of a flexible joint, while dead cracks can be repaired by injecting them with a resin.