Concrete structures may require repair for various reasons, such as deterioration caused by chemical attacks. To address such issues, different types of materials are used, such as unmodified Portland cement mortar or grout, latex modified Portland cement mortar or concrete, quick setting non-shrink mortar, and polymer concrete. The selection of these materials depends on factors such as their performance, cost, compatibility with the damaged structure, and ease of application.
However, the success of the repair work depends not only on the choice of materials but also on the proper execution procedure. The failure or partial failure of the bond between the old and new concrete is the main reason for the failure of the repaired concrete. Therefore, it is crucial to prepare the base concrete carefully to ensure a standard of bond that develops between the old and new concrete.
In cases where deterioration is due to chemical attacks, it may be necessary to use a different cement or protective coatings. Overall, repairing concrete structures requires attention to detail, including the selection of appropriate materials and the proper execution procedure.
Selection Criteria for Repair Materials
When choosing a concrete repair material, there are several factors that need to be considered. These factors include the ease of application, cost, available labor skills and equipment, shelf life of the material, and pot life of the material. It is important to select a material that is easy to apply and does not require specialized skills or equipment to complete the repair job. Additionally, cost and availability of the material should be taken into account as well.
Another important factor to consider when selecting a concrete repair material is the type of damage that needs to be repaired. Some materials are better suited for certain types of damage than others, so it is important to choose a material that is compatible with the type of damage that needs to be repaired. The compatibility of the repair material with the damaged concrete is also an important consideration, as using a material that is not compatible can result in further damage.
The appearance of the finished surface is also an important factor to consider when selecting a concrete repair material. The repair material should match the color and texture of the existing concrete as closely as possible to ensure a seamless repair. The co-efficient of thermal expansion and permeability of the material should also be considered, as these properties can affect the durability and longevity of the repair.
Finally, the durability and speed of the repair should also be taken into account when selecting a concrete repair material. The material should be able to withstand the environment and any potential future damage, while also being able to be applied quickly and efficiently to minimize downtime. Additionally, the corrosion resistance property of the material is also an important consideration, as corrosion can significantly reduce the lifespan of the repair.
Common Repair Materials
Following are the some of the common repair materials used for repair or rehabilitation or strengthening of the concrete structures:
1. Unmodified Portland Cement Mortar or Grout
Portland cement mortar or grout is a commonly used material for repairing damages to concrete structures. One of the reasons for its popularity is its wide availability and low cost. The material is composed of ordinary Portland cement and an appropriate aggregate.
When it comes to small repair works, cement mortar is the preferred option. However, for larger areas requiring repair, cement concrete is usually selected. Both materials have their respective advantages and are utilized according to the specific requirements of the project at hand.
In summary, the use of Portland cement mortar or grout is a popular choice for repairing concrete structures due to its availability and cost-effectiveness. Depending on the size of the repair, either cement mortar or concrete may be selected as the appropriate material.
2. Latex Modified Portland Cement Mortar or Concrete
Latex modifier concrete is a type of repair material that is specifically designed to protect concrete structures from chloride attack. This is particularly important when a low water-cement ratio is used in the initial construction of the structure. Essentially, latex modifier concrete is very similar to ordinary Portland cement mortar or grout, but with the addition of a latex emulsion. This modification helps to reduce the ingress of water and other harmful substances, thus improving the overall durability of the structure.
Despite the addition of latex emulsion, the strength of latex modifier concrete is the same as that of ordinary mortar or grout. However, the use of a latex modifier can have a significant impact on the overall strength and durability of the cement. Therefore, it is important to carefully consider the service conditions of the structure before deciding whether to use this type of repair material.
When using latex modifier concrete for sections that are up to 30mm deep, it is recommended to use a ratio of 1 part cement to 3-3.5 parts fine aggregates. The water ratio should be 0.3, and the latex solid cement ratio should be between 0.1 and 0.2 by weight. For sections that are deeper than 30mm, the recommended proportions are 1 part cement to 2.5-3 parts fine aggregate to 1.5-2 parts coarse aggregate. By following these guidelines, it is possible to create a strong and durable repair material that can help to protect concrete structures from chloride attack and other forms of damage.
3. Quick Setting Non-shrink Mortar
When concrete surfaces develop cracks due to shrinkage, a specific material is used to repair them. This material is designed to create a strong bond with the existing concrete surface. By using appropriate admixtures in conjunction with this repair material, the strength of the concrete is increased, and its workability and bond are improved. Additionally, the curing time required for the repaired surface is reduced.
One popular type of polymer concrete used for repairs is the epoxy concrete system. It consists of curing agents that react with the epoxy to form a strong bond with the old concrete. Alternatively, a methyl methacrylate monomer combined with an inhibitor and promoter can also be used for repairs. Epoxy systems are readily available in formulated repair materials and can be customized to suit the specific requirements of the repair job.
A quick-set non-shrinking mortar is also an effective material used to repair concrete surfaces. It sets rapidly and does not shrink as it cures, ensuring a durable repair. This type of mortar is particularly useful in situations where rapid repairs are required, such as in high-traffic areas or industrial settings. By using these types of repair materials, it is possible to restore damaged concrete surfaces to their original strength and durability.
Fig. 3: Quick-set Non-shrinking Mortar