Concrete repair works involve the replacement and jacketing of concrete structural members, which requires the use of materials with certain properties. It is crucial for these materials to possess good bonding properties with the existing materials to ensure a strong and durable repair. In addition, they should be non-shrinking to avoid any potential damage or cracks to the repaired structure.
The replacement of concrete is necessary when the structural member has been damaged beyond repair. On the other hand, strengthening of existing concrete members can be achieved through the addition of concrete, along with reinforcement, in the form of jackets. The materials used for such repair works must meet the aforementioned criteria to ensure a reliable repair and prevent further damage to the structure.
Materials for Concrete Repair, Replacement and Jacketing
There are various materials available for jacketing and replacement of concrete. We will discuss about them below.
Ordinary Portland cement Concrete and Mortar:
A material commonly used for replacement and jacketing of concrete and masonry structures is cost-effective and does not require specialized workmen for repair works. This material exhibits similar properties to existing concrete structures and is composed of high early strength cement and an expansive component to prevent shrinkage cracks. The expansive agents used in this material include aluminium powder, coke powder, anhydrous calcium sulfo-aluminate, and calcium oxide. These materials have excellent bonding properties with existing concrete in structures.
Shotcrete:
Shotcrete is a type of concrete that is sprayed onto prepared concrete or masonry surfaces under pressure, using a nozzle. The pressure compacts the shotcrete, resulting in a dense and homogeneous mass. It is commonly used for repairing damaged concrete or adding a jacketing layer. Reinforcement in shotcrete typically consists of welded wire fabric and deformed bars, which are attached to the existing concrete surface to improve the bond between the old and new concrete. Surface coatings such as epoxy bonding agents, latex modified cement slurries, or neat cement slurries may also be used to enhance the bond between the two surfaces. One of the advantages of shotcrete is that it does not require any formwork and can be applied on various surfaces, including inclined, vertical, and roof slabs, resulting in excellent adhesion and compaction due to the application under pressure. The use of a low water-cement ratio in shotcrete leads to high strength and low shrinkage in the repaired concrete. Additionally, shotcrete has lower permeability compared to ordinary concrete, providing better protection for steel against corrosion. There are two methods for applying shotcrete for concrete repair: wet mix and dry mix. In the wet mix process, the concrete materials are mixed with water before being used for repair work. In the dry mix process, compressed air is used to propel the mixture of dry concrete without water through a delivery hose to the nozzle, where water is added separately through another hose. The water and dry mix concrete are then spread on the existing concrete surface.
Fig: Shotcrete application in concrete repair
Skilled workmen are essential for the proper application of shotcrete. Shotcrete, which is a specialized technique used in construction, requires expertise and proficiency to ensure its correct application. Skilled workmen possess the necessary knowledge and experience to properly handle the equipment and materials used in shotcrete application, as well as to accurately adjust the mixture proportions and control the spraying process. Their expertise ensures that shotcrete is applied with precision, resulting in a high-quality and durable finished product. Proper training and experience are crucial in order to achieve optimal results in shotcrete applications, making skilled workmen an indispensable asset in this specialized field of construction.
Polymer modified concrete and mortar:
Polymer modified concrete and mortar are prepared by incorporating polymer latexes, which form a continuous film upon drying. This film serves to bind the cement hydrates together, creating a cohesive network that is reinforced by the interpenetration of the polymer phase and the cement hydrate phase. As a result, the matrix formed binds the aggregate more effectively and enhances the properties of both mortar and concrete. Compared to ordinary concrete and mortar, polymer modified versions boast improved workability and water retention properties. This feature allows for a reduction in the amount of time required for curing of repaired or replaced concrete members. Although the use of polymer modified concrete and mortar does not increase the compressive strength of concrete, it does contribute to a higher tensile strength in concrete members. A notable benefit of using this material is its ability to improve adhesion and bond with existing concrete, as well as significantly reducing permeability. The reduced permeability of concrete also leads to increased durability of reinforcement, as the low risk of corrosion minimizes damage.
Fiber-reinforced plastics (FRP) Concrete:
Fiber-reinforced plastics or polymers are frequently utilized in the strengthening of concrete and masonry structures. This material serves as a substitute for steel plate bonding and is particularly effective in enhancing the strength of columns through exterior wrapping or jacketing. One of the main advantages of FRP is its high strength to weight ratio, as well as its resistance to corrosion. Carbon fibers, glass fibers, and aramid fibers are among the commonly used fibers in concrete, while polyester, vinyl ester, and epoxy are the commonly used resins.
Fiber-reinforced concrete is classified into various types, named after the type of material used. These include carbon fiber reinforced polymer concrete, glass fiber reinforced polymer concrete, and aramid fiber reinforced polymer concrete. By using FRP, the strength and durability of concrete and masonry structures can be significantly improved, making them more resistant to damage and wear.
Epoxy concrete:
Epoxies are a type of polymer that have gained popularity due to their excellent binding properties, mechanical strength, chemical resistance, and ease of use. These qualities make epoxies an ideal choice for use in civil engineering applications such as high-performance coatings, adhesives, injection grouting, industrial flooring, and grouting.
Epoxies are particularly effective in repair works where low viscosity resins can be injected into fine cracks, while higher viscosity materials can be used for surface coating or filling larger holes and cracks. They can also be used for gluing steel plates to distressed members.
One of the most common applications of epoxy concretes in civil engineering is to bond plastic concrete to hardened concrete. They are also useful in bonding rigid materials to one another, patch work, and painting over concrete to give color, resistance to chemicals, water, and abrasion.
In summary, epoxies are a versatile polymer with a wide range of civil engineering applications due to their superior mechanical properties and ease of use. They can be used to repair fine cracks or fill larger holes and cracks, bond materials to one another, and provide color, chemical resistance, and abrasion resistance to concrete surfaces.
Epoxy mortar:
Epoxy mortar is a type of mortar that is created using a combination of epoxy and appropriately sized aggregate, typically sand. This type of mortar is known for its high compressive strength and high tensile strength. Additionally, its modulus of elasticity is lower than that of cement concrete.
Epoxy mortar is commonly used for repairing larger void spaces. When epoxy is added to cement mortar or concrete, it can be thought of as incorporating a second binder into the mixture. Overall, epoxy mortar is a durable and effective option for a variety of construction and repair projects.