Concrete is a highly versatile and commonly used construction material, offering many advantages over steel and other materials. Despite its benefits, defects in concrete can often occur, presenting themselves in various forms such as cracks, spalling, exposure of reinforcement, excessive deflections, and other signs of distress. In some cases, corrosion of the reinforcement may lead to cracking and spalling of the concrete, which can result in a reduction in the structure’s strength. When these situations arise, repairs of affected areas become necessary, and in some cases, the replacement of the entire structure may be required.
To address such defects and failures in concrete structures, there are several techniques and materials available for repair and rehabilitation. These methods involve the use of different materials such as polymers, epoxies, mortars, and grouts to restore the structural integrity of the affected zones. The choice of the repair technique and materials depends on the type and extent of the damage, the service conditions, and the desired lifespan of the repaired structure.
One of the most common techniques used for repairing cracks in concrete structures is crack injection. This method involves injecting a suitable resin or polymer into the crack to fill the void and prevent further cracking. Another technique is surface sealing, which involves applying a coating or membrane to the surface of the concrete to prevent water ingress and protect against further damage.
For more severe cases of damage, such as spalling or corrosion, concrete removal and replacement may be required. In such situations, the affected area is cut out, and new concrete is poured to restore the structural integrity of the damaged section. Another method is the use of overlays, where a thin layer of new concrete or a polymer-modified cement-based material is applied to the surface of the existing concrete to improve its strength and durability.
In summary, defects in concrete can be a significant concern, potentially leading to reduced strength and structural failure. However, various techniques and materials are available for repairing and rehabilitating affected zones, depending on the extent of the damage and service conditions. By using appropriate repair methods, the structural integrity of the concrete can be restored, ensuring the safety and longevity of the structure.
Causes for Failures or Defects in Concrete Structures
Concrete structures can fail for various reasons. The first major cause is related to structural deficiency, which can result from a flawed design and detailing or incorrect assumptions regarding the loading criteria. When these issues arise, the structural integrity of the concrete may be compromised, leading to failure.
Another reason for structural deficiency is defects that occur during construction. The use of inferior and substandard materials, poor workmanship, and a lack of quality control and supervision can all contribute to this type of failure. In such cases, the concrete may not meet the necessary standards to support the intended load, which can lead to structural failure.
Natural disasters and other events can also cause concrete structures to fail. For example, fire, floods, and earthquakes can all inflict significant damage on concrete structures, compromising their structural integrity and causing them to fail. This type of damage may require extensive repairs or even complete reconstruction.
Another cause of concrete structure failure is chemical deterioration and marine environments. Exposure to harsh chemicals or seawater can cause concrete to deteriorate over time, eventually leading to failure.
Physical wear and tear is also a common cause of concrete structure failure. Abrasion, impact, and dampness can all contribute to the deterioration of concrete, leading to structural failure.
Finally, movement of concrete can occur due to a variety of factors, including settlement of the foundation and thermal expansion. These types of movements can cause stress on the concrete, leading to cracks and other structural defects that can ultimately result in failure.
Identification of Failures and Defects in Concrete Structures
The accurate diagnosis of a structure’s condition is crucial. A correct diagnosis should determine the cause, nature, and extent of damage, as well as any weaknesses or deterioration that may have occurred. It is essential to ensure that the selected materials and repair techniques are appropriate, as an incorrect diagnosis can lead to the failure of the repaired area. Furthermore, after completing any necessary repairs, it may be necessary to verify the serviceability of the structure.
A faulty diagnosis can have serious consequences. If the diagnosis is incorrect, the materials and repair techniques used to fix the structure may not be appropriate. This can lead to the failure of the repaired area and require additional repair work, which can be costly and time-consuming. Therefore, it is important to accurately determine the cause, nature, and extent of the damage before initiating any repairs.
In addition to selecting the appropriate repair techniques and materials, it is also important to check the serviceability of the structure after completing any repairs. This will ensure that the structure is functioning as intended and that any potential issues are addressed promptly. In summary, an accurate diagnosis of a structure’s condition is essential to ensure the effectiveness and longevity of any repairs.
Need for Repair and Rehabilitation of Concrete Structure
Structural repairs may become necessary due to various reasons. One of these reasons is a faulty design of the structure, which can result in weaknesses and vulnerabilities that require fixing. Another reason for structural repairs can be improper execution and bad workmanship during the construction process, which can lead to issues that require addressing.
In addition, extreme weathering and environmental conditions can also cause structural damage, making repairs necessary. High degrees of chemical attack can also be a contributing factor to structural issues, leading to the need for repairs.
Lastly, the ageing of the structure can cause it to become weakened and deteriorated, necessitating repairs to maintain its integrity and safety. All of these factors can result in the need for structural repairs, which should be addressed promptly to ensure the safety and longevity of the structure.
Techniques for Repairs and Rehabilitation of Concrete Structure
The repair or restoration of a structure depends on several factors, including the cause, extent, and nature of damage, the function and importance of the structure, availability of suitable materials and facilities, and knowledge of the long-term behavior of the materials used for repair work. Depending on the specific requirements, repairing techniques may be superficial or involve the replacement of part or all of the structure. To carry out repairs, the techniques can be classified into three major groups: injection into cracks, voids, or honey-combed areas; surface treatment; and removal and replacement of defective or damaged material/area.
New materials have been developed for repairing and restoring damaged structures using any one of the above methods. These materials offer a range of benefits, such as improved durability and strength. The use of injection techniques involves filling voids and cracks with suitable materials, while surface treatment is a technique that can help to restore the surface of the structure. In cases where the damage is significant, the removal and replacement of defective or damaged material or area may be necessary.
In summary, the appropriate technique for repairing or restoring a structure will depend on various factors, and a thorough assessment is necessary before deciding on the method. The development of new materials has expanded the range of options available for carrying out repairs, and the use of advanced techniques has significantly improved the quality and durability of the repairs.
Materials for Repairs and Rehabilitation of Concrete Structure
Cement, Cement Grouts, etc.
Repairing damaged areas and cracked portions in concrete typically involves the use of cement-based materials. This is because cement is the active ingredient in concrete. One possible option for repairing these areas is using dry pack, which is a mixture of rich cement concrete or cement grouting. Another effective method is to spray concrete or cement sand grout using high-pressure nozzles, a process known as “shotcrete” or “guiniting”.
Shotcrete or guiniting can be particularly useful when repairing large surface areas. The process can be carried out with or without steel reinforcing mesh or steel fibers. These materials may provide additional structural support, but they are not always necessary for successful repairs. Ultimately, the choice of repair method and materials will depend on the specific needs of the project at hand.
Resin based Repairs of Concrete
Resins, such as those derived from the epoxide, polyester, acrylic, or polythene families, are commonly used in repair work. However, a thorough understanding of the chemical and physical properties of these materials is crucial to ensure their effectiveness in structural repairs, particularly over time and in challenging environments.
Epoxy resin systems are particularly useful in civil engineering applications, such as grouting cracks, repairing eroded concrete structures, and conducting emergency repairs of bridges, aqueducts, and chemically corroded columns and beams. These materials are frequently used in restoration and repair work, where properties such as high strength, excellent adhesion, quick curing, and chemical resistance are essential.
Epoxy-based resins are especially popular for repair work due to their desirable properties. These resins offer high strength, enabling their use in thin sections, as well as excellent adhesion, making them ideal for small patches. Additionally, they cure quickly, saving time, and exhibit high chemical resistance. Overall, epoxy resins are one of the most commonly used materials in repair and restoration work.
Epoxy Resins for Concrete Repair
Resin mortar is a type of material that can be created by adding fillers like coarse sand or calcined bauxite grit to it. When the resin and hardener are combined, a chemical reaction begins immediately. The pot-life of most combinations typically lasts between 30 to 60 minutes. Once cured, epoxy resin offers excellent strength and adhesive properties, as well as resistance to many chemicals and good water proofing. Different hardeners can be used with epoxy resin to obtain a wide range of properties. Epoxy resin forms an irreversible system when it cures, making it thermosetting in nature.
The characteristic properties of cured epoxy resin systems make it suitable for the repair and rehabilitation of concrete structures. It has a high adhesive strength to almost all materials, low shrinkage during curing, exceptional dimensional stability, and natural gap filling properties. Epoxy resin is thermosetting, which means it does not melt, and it is resistant to most chemicals and environments. It can even cure in wet conditions and underwater for selected grades. Additionally, it is easy to apply.
Procedure of epoxy resin grouting
To repair cracked surfaces, a systematic approach is followed which includes identifying the location of the cracks and then cleaning the affected area. After that, nozzles are drilled into the surface at suitable intervals, which will be used for grouting with an epoxy putty. The epoxy mixture is then injected into the cracks using a grout pump. The nozzles through which the grouting is done are sealed to ensure that the epoxy mixture fills the cracks and does not leak out.
For effective grouting, a grout vessel is used, which is a pressure vessel designed to withstand a pressure of 10-15 kg/cm2. The grout vessel has an inlet and an outlet for the resin mixture, a pressure gauge, and a connection for compressed air with a regulator for pressure grouting. The vessel is filled with a pre-mixed resin and hardener, and the activated resin is then pumped into the cracks through the nozzle. This process is repeated until all the cracks are filled, which helps to improve the load carrying capacity of the structure once the epoxy resin has cured.
Bonding Old to New Concrete
Epoxy resin combined with a special polyamide hardener has proven to be a successful bonding agent for old and new concrete. The process involves removing any loose or damaged concrete using mechanical means or water jet, and ensuring that the surface is completely dry before application. A stiff nylon brush is then used to apply a suitable epoxy resin, consisting of unmodified solventless epoxy resin and the aforementioned special grade of polyamide hardener.
It is important to note that epoxy resins are not typically used as primary construction materials due to their high cost. Instead, they should be used judiciously, primarily in emergency situations where other materials cannot provide the necessary strength or performance. Despite this, the advantageous properties of epoxy resin systems have led to their increased use in challenging conditions such as underwater repairs of dams and ships. It is likely that even more new applications will be discovered for epoxy and other synthetic resins in the future.
Polymer Concrete Composites
Polymer concrete composites have emerged as a solution to address the deficiencies often found in ordinary structural concrete. They can be applied as a surface coating or impregnated into the structure to enhance its performance. Polymer concrete composites have been in use for structural applications since the 1950s and offer several advantages, including high strength, improved durability, and resistance to chemicals and acids. There are three types of polymer concrete composites: polymer impregnated concretes (PIC), polymer concretes (PC), and polymer cement concretes or polymer modified concretes (PCC or PMC).
In PICs, monomers such as styrene, methyl-methacrylate (MMA), and polymethyl methacrylate (PMMA) are impregnated into the pores of the hardened concrete, effectively filling them up and making them impermeable to water and resistant to chemical attack. PC, on the other hand, replaces cement and water as the sole binder in the composite, with the polymer serving as the primary binding material. Finally, PCCs and PMCs involve adding a polymeric additive, such as latex or pre-polymer, to the traditional cement mixture during the mixing stage.
By utilizing polymer concrete composites, the limitations of ordinary structural concrete can be overcome, resulting in improved performance and enhanced durability. The versatility of these composites allows for various applications in the construction industry, making them a valuable advancement in modern engineering.
Polymer concrete composites are becoming increasingly popular for repairs and restoration work in damaged structures, as they offer superior durability, excellent bond to the parent concrete structure, abrasion and wear-resistant properties, and resistance to chemicals such as chlorides and acids. These composites are classified into three types, all of which are useful for post-distress and post-failure applications. One significant advantage of polymer concrete composites is their low water absorption rate, making them ideal for repairing cracks and replacing damaged concrete due to corrosion of reinforcement. The damaged portions can be easily chipped off and replaced with polymer concrete, providing a reliable and long-lasting solution for structural repairs. Additionally, polymer concrete composites also serve as effective sealants, providing a protective barrier against moisture, chemicals, and other environmental factors that can further damage the structure.
Sealants
Concrete structures require reliable and effective sealants to seal any cracks that may appear in them. These sealants must meet several requirements to ensure the structural integrity and serviceability of the structure. One important function of these sealants is to protect the structure against the passage of harmful liquids, gases, and other undesirable substances that could negatively impact the quality of the concrete.
When repairing a cracked surface, the cracks are first widened along their exposed face and are then filled with sealant. This process, known as pointing up, helps to ensure that the sealant can effectively seal the crack and prevent any further damage from occurring.
The selection of the appropriate sealant for a particular application is a critical step in ensuring the long-term performance of the concrete structure. Factors such as the type of crack, the expected movement of the structure, and the type of exposure to external elements must all be considered when choosing a sealant.
Overall, effective sealants play a crucial role in maintaining the integrity and longevity of concrete structures, and careful consideration should be given to their selection and application.
Surface Treatment to Concrete
Concrete is a construction material that is commonly used due to its strength and durability. However, to further enhance its durability, various techniques can be employed. One such technique is the application of different materials on the concrete surface to make it more resistant to chemical attack, hardened, and waterproof.
These additional materials can improve the overall quality of the concrete, making it more long-lasting and robust. By increasing its resistance to chemical attack, the concrete can better withstand exposure to harsh chemicals and substances that may otherwise cause damage. Furthermore, the hardening of the concrete can help to prevent cracking and other forms of damage that can occur over time.
In addition, making the concrete waterproof can be particularly useful in areas that experience high levels of rainfall or water exposure. Water can penetrate concrete over time, causing structural damage and reducing its durability. By making the concrete waterproof, it can resist the effects of water damage, making it more long-lasting and reliable.
Overall, the application of different materials on the surface of concrete can significantly increase its durability, making it more resistant to chemical attack, hardened, and waterproof. By employing these techniques, the quality and reliability of the concrete can be greatly improved, making it a more valuable construction material for a variety of applications.
Some of the commonly used surface treatments are:
Concrete surfaces can be made more resistant to abrasion and less prone to dust by applying solutions of sodium silicate, magnesium or zinc sulphates, or silico fluorides once the concrete has hardened and dried. Alternatively, drying oils like tung or linseed oil can be used. In some cases, carborundum, fused alumina, or finely divided iron aluminum chloride preparations can be added to the surface layer during the placement of fresh concrete. If the traffic on a floor is not too heavy, floor paints can provide a reasonable level of durability. Paints containing synthetic resins, such as polyurethanes, epoxies, or chlorinated rubber, offer even greater wear resistance and protect against solutions of salts and dilute acids. Applications of sodium silicate and silico fluoride can protect against mild attacks by aqueous solutions or organic liquids. Bitumen and coal tar can protect against insects and borers. Some plastic materials, rubber latex, glass fiber coatings, and PVC linings have also been used successfully to improve the durability of concrete.
Steel Fiber Reinforced Concrete
The utilization of small diameter steel fibers in concrete has been proven to enhance various properties of concrete, notably its tensile strength, impact resistance, and wear resistance. Steel fiber reinforced concrete (SFRC) has found practical applications in repairing and restoring deteriorated concrete structures. The addition of steel fibers in SFRC contributes to improved performance and durability, making it a suitable choice for repairing and restoring concrete structures that have experienced damage or deterioration over time. The incorporation of small diameter steel fibers in concrete has shown promising results in enhancing the tensile strength and impact resistance of SFRC, making it an effective solution for repairing and restoring concrete structures that are subjected to significant mechanical stress or wear. Additionally, the use of SFRC has been found to be effective in mitigating cracking and improving the overall performance and service life of repaired or restored concrete structures. The improved properties of SFRC due to the addition of steel fibers make it a reliable and efficient material for use in repairs and restoration projects of concrete structures, offering enhanced durability and longevity to the rehabilitated structures.
Concrete structures that have been damaged can be effectively repaired by removing the affected portions and applying Steel Fiber Reinforced Concrete (SFRC) to the sides and bottom of the damaged areas using guiniting or shotcrete techniques. SFRC, known for its enhanced wear and tear resistance as well as abrasion resistance, has proven to be a successful choice for repairing industrial floors and bridge decks, whether polymer concrete is used or not.
Other Materials for Repair and Rehabilitation of Concrete
Various materials are available for repairing different types of structures. For example, special chemical grouts can be used for repairing existing foundations. These grouts help in compacting the soil underneath and offer protection to the reinforcing steel present in the foundation. Similarly, superplastized fiber reinforced concrete is used for repairing underground structures and machine foundations. Certain chemicals and surface coatings are also used to seal cracks in structures like water tanks, which can help in protecting the steel from corrosion. There are special paints available that can be applied to the concrete surface or bars to make them resistant to aggressive environments.
With the increasing number of structures experiencing damages, repairing and rehabilitating these structures have become more critical. Table below shows the materials that are generally recommended for repairing concrete structures. Epoxy resins and concrete composites have shown high potential as promising repair materials. It is crucial to detect deficiencies in concrete and steel of an existing structure and execute immediate remedial measures to prevent further deterioration of the structure. This will result in significant savings in the maintenance cost. As the old saying goes, “prevention is better than cure,” and this holds true for concrete structures both during construction and when the structure shows initial signs of distress.
Materials for Repair of Concrete
| Repair Operation | Material | Comments |
| Sealing of fine cracks | Epoxy resins | – Good bonding properties even in the presence of moisture |
| Sealing of large cracks and joints | Portland cement Mortar Polymer mortar Putties and caulks | – Well – compacted – Good bonding properties – Based on synthetic polymers and tars |
| General sealing of surface | Synthetic polymers and asphalt coatings | |
| Localized patching of surfaces | – Concrete or mortar using Portland cement – Rapid-setting cements – Polymer resins; epoxies; polyesters | – Calcium aluminate and regulated-set cements – Good bonding |
| Repair Operation | Material | Comments |
| Overlays and shotcrete | – Portland cement concrete – Steel fiber reinforced concrete – Latex modified concrete – Polymer concrete – Asphaltic concrete | – Quick-setting admixtures – Resistance to cracking – Good bonding |