RCC Structural Members Retrofitting – Types, Selection, and Procedures

This article is about Types, Selection, and Procedures of RCC Structural Members Retrofitting, retrofitting of concrete structures pdf, is code for retrofitting of RCC structure, Retrofitting of RCC columns, Retrofitting techniques, jacketing method of Retrofitting and Retrofitting of RCC columns.

RCC Structural Members Retrofitting

Retrofitting of reinforced concrete (RCC) structural members is a common practice to restore their strength and prevent further damage caused by deterioration or poor workmanship during construction. In order to carry out the retrofitting process, the first step is to investigate and diagnose the extent of cracks or other damage in the concrete elements. Once this has been determined, a suitable retrofitting technique and compatible materials can be selected.

There are various techniques used to retrofit structural members, each with its own advantages and limitations. One such technique is section enlargement, which involves increasing the cross-sectional area of the structural member to enhance its load-carrying capacity. Another technique is external plate bonding, which involves attaching steel or composite plates to the exterior of the structural member to improve its strength and stiffness.

External post-tensioning is another retrofitting technique that can be used to increase the load-carrying capacity of a structural member. This involves installing tensioned cables or rods on the exterior of the member to create compressive forces within the concrete, which in turn can help to counteract the tensile stresses that cause cracking and other forms of damage.

Grouting is another commonly used retrofitting technique that involves injecting a cement-based or resin-based material into the cracks or voids in the concrete. This helps to improve the overall strength and durability of the member by filling any gaps or voids that may be present.

Finally, fibre reinforced polymer composites (FRP) are a newer and increasingly popular retrofitting technique that involves applying layers of high-strength fibre-reinforced polymers to the exterior of the structural member. This technique has several advantages, including high strength-to-weight ratio, durability, and ease of installation. Ultimately, the choice of retrofitting technique will depend on the severity of the damage and the required capacity to be regained.

When do RCC Structural Members Need Retrofitting?

RCC (Reinforced Concrete) structures are prone to several problems that need to be addressed for their safe and effective operation. One of the most common problems is the development of structural cracks. These cracks may occur due to a variety of factors, such as overloading, poor construction practices, or inadequate design.

Another significant problem that RCC structures can face is damage to structural members. This damage may result from various factors, including exposure to harsh environmental conditions, impact or collision, or inadequate maintenance. Structural members that are damaged can compromise the overall stability and safety of the entire structure.

Excessive loading is another common issue that RCC structures may encounter. Overloading can lead to structural failure or collapse if the structure is not designed to handle the additional weight or if the load exceeds the design limits.

Errors in design or construction can also contribute to problems in RCC structures. These errors may include improper selection of materials, inadequate reinforcement, or poor workmanship during construction.

Modifications made to the original structural system can also pose a risk to the stability and safety of the RCC structure. Alterations made to the original design or construction may not have been properly evaluated for their impact on the overall structural integrity.

Seismic damage is also a major concern for RCC structures, especially in regions that are prone to earthquakes. The dynamic forces exerted during an earthquake can cause significant damage to the structure, compromising its overall stability.

Read Also: Sketches/Maps of Concrete Cracks Observed in Visual Inspections

Retrofitting Methods for RCC Structural Members

Fiber reinforced polymer (FRP) composites are a popular material used in the construction industry due to their high strength and durability. One application of FRP composites is in external plate bonding, which involves attaching FRP plates to existing concrete structures to increase their load-bearing capacity.

Another technique used in concrete reinforcement is near surface mounted FRP bars or strips, which are placed on the surface of the concrete and anchored into the substrate. This method is effective in improving the flexural and shear strength of reinforced concrete structures.

Section enlargement is a process that involves adding additional material to a section of a concrete structure to increase its load capacity. This is achieved by attaching FRP strips or plates to the section, which can improve the structure’s resistance to bending and shear forces.

External post-tensioning is a technique used to reinforce concrete structures by applying tension to the concrete using external tendons. This method is effective in increasing the load capacity of concrete structures and improving their resistance to external forces.

Grouting is a process used to fill voids or gaps in concrete structures with a cement-based grout material. This method is commonly used to improve the structural integrity of concrete structures by filling in any gaps or voids that may have developed over time.

Factors Consideration for Retrofitting Methods Selection

When it comes to enhancing the strength of existing concrete structures, several factors must be taken into consideration. The first factor is the current strength of the concrete. It’s important to have a clear understanding of the strength of the existing concrete before any enhancement work can be done.

Another crucial factor to consider is the accessibility to the work areas. This can greatly impact the cost and time required for the construction and maintenance of the structure. Any limitations on access can also affect the methods and equipment that can be used for the enhancement work.

The magnitude of the strength to be enhanced is also an essential consideration. Depending on the specific requirements of the structure, the level of enhancement required can vary. This can significantly impact the materials and techniques used for the work, as well as the overall cost of the project.

The cost of construction and maintenance is also a critical factor that must be taken into account. Enhancing the strength of a concrete structure can be a costly undertaking, and it’s essential to ensure that the cost is reasonable and justifiable.

Time constraints can also impact the enhancement process. If the project is time-sensitive, it’s important to take this into account during planning and implementation to ensure that the work is completed on time.

Clearance issues are another factor to consider. Depending on the location and size of the structure, there may be restrictions on the amount of space available for the work. This can impact the methods and equipment used for the enhancement work.

Seismic effect consideration is also essential, especially in areas prone to earthquakes. The work done should aim to improve the structure’s ability to withstand seismic activity.

Finally, environmental aspects should also be taken into account. The use of certain materials and techniques can have an impact on the environment, and it’s crucial to ensure that the work is done in an environmentally responsible way.

Retrofitting Strategy   

When retrofitting a structural member, it is important to specify the performance requirement that the member must meet. This ensures that the retrofitting work is effective and that the structure is safe to use.

To begin the retrofitting process, an overall plan should be developed. This plan should include an inspection phase to assess the current condition of the structural element, as well as the selection of an appropriate retrofitting method. Once the method has been selected, the design of the retrofitting structure should be completed and the actual retrofitting work can begin.

During the inspection phase, the structural element that needs to be retrofitted should be thoroughly examined. This evaluation will help determine if the structure is meeting the required performance standards. If it is found that the structure does not meet these standards, and retrofitting is still desired, then the design of the retrofitting structure can proceed.

When selecting a retrofitting method, it is important to consider the materials that will be used, the structural specifications, and the construction method. Once these decisions have been made, the performance of the structure after retrofitting should be evaluated to ensure that the structure is meeting the required performance standards.

If it is determined that the retrofitting structure is capable of fulfilling performance requirements, then the retrofitting work can be executed. By following this process, it is possible to ensure that the retrofitted structure will be safe to use and will meet the performance requirements set forth at the beginning of the retrofitting process.

How to Investigate and diagnose cracks?

When cracks appear in RCC structural members, it is important to investigate the root cause of the cracks. If it is determined that the cracks are due to corrosion of steel, additional field investigations and testing are necessary. Both destructive and non-destructive testing methods can be used to gather more information.

Destructive testing methods such as core testing can be used to determine the degree of cracks, spalling of concrete cover, and corrosion of steel for each member. Non-destructive testing methods such as the Rebound Hammer, Ultrasonic pulse velocity method, and rebar location can also be used to assess the extent of the damage.

To classify the cracks, the width of the crack is measured and compared to established criteria. Based on the width of the crack, it can be classified as hairline, fine, medium, or coarse. The width of the crack is an indicator of the severity of the damage and can be used to determine the appropriate repair and maintenance strategies.

Table 1 Classification of Cracks based on Crack width

Crack Width	Classification of crack
Upto 1mm	Thin cracks
1 to 2 mm	Medium cracks
More than 2mm	Wide cracks

4. Determine the condition of concrete i.e. porosity, segregation, and thickness and condition of cover.

5. Specify the extent of damage to the reinforcement bars.

6. Investigation about failure of previous repairs if any.

Read Also: Types of Cracks in Fresh and Hardened Concrete

Materials Used for Repair of concrete cracks

The materials commonly used for repairing cracks and rehabilitating RCC structures include a variety of options. These materials are specifically designed to address the unique needs of concrete structures, such as their susceptibility to cracking and deterioration over time.

Some of the most popular materials used for this purpose include epoxy resins, which are known for their ability to bond strongly to concrete surfaces and provide excellent protection against future cracking. Additionally, polymer-modified cement mortars and grouts are often used to repair cracks and prevent further damage, as they can be easily applied to the surface of the concrete and create a strong, durable bond.

Other materials commonly used for rehabilitating RCC structures include carbon fiber wraps and plates, which can be used to reinforce weakened areas of the concrete and prevent further cracking. These materials are particularly useful in situations where the concrete has been subjected to significant stress or damage and requires additional support to prevent structural failure.

Overall, the selection of materials used for repairing cracks and rehabilitating RCC structures will depend on a variety of factors, including the severity of the damage, the location of the affected area, and the desired outcome of the repair process. With the right materials and techniques, however, it is possible to effectively restore the structural integrity of RCC structures and extend their useful lifespan for many years to come.

1. Portland Cement

Cement slurry injections can be used to seal gaps, pores, or cracks. Polymers can be added to the slurry to improve its effectiveness. Another method of replacing concrete cover or adding a surface coating is to use a motor, which may or may not contain plasticizers. Microcrete, which involves guniting or shotcreting, can also be used as a replacement for concrete or cover concrete. Finally, concrete can be used with or without plasticizers to replace existing concrete.

2. Polymer modified concrete (PMC)

Polymer modification is a popular method used to enhance the properties of concrete and mortar. This technique involves incorporating a polymer latex, such as acrylates or SBR (Styrene Butadiene Rubber), into the mix. These polymers are added to the cement mixture to improve its performance and make it more durable.

One of the benefits of using polymer-modified concrete or mortars is that it can improve the strength and durability of the final product. The addition of the polymer latex helps to increase the bond strength between the cement and aggregate, making it less likely to crack or fail under stress.

Another advantage of using polymer modification is that it can improve the workability and consistency of the mix. This can make it easier to apply and shape, resulting in a smoother finish. Additionally, polymer-modified concrete and mortars are often more resistant to water and chemicals, making them ideal for use in harsh environments.

Overall, polymer modification is a valuable technique that can enhance the properties of concrete and mortars. The use of polymer latex such as acrylates and SBR has become increasingly popular due to its ability to improve strength, durability, workability, and resistance to water and chemicals.

3. Epoxy Resins

Epoxy resins can be used for injection or concrete repairs, and they may or may not contain filler materials such as quartz sand. The addition of filler materials can enhance the mechanical properties of the epoxy resin and improve its ability to withstand physical stress. This is particularly useful in concrete repairs where the epoxy resin is expected to bond with the surrounding concrete and provide structural support.

Similarly, polymer resins can also be used for concrete repairs, either with or without the addition of filler materials. Like epoxy resins, the addition of fillers can improve the mechanical properties of the polymer resin and make it better suited for use in concrete repairs. Polymer resins are often preferred for their ability to penetrate deeply into the cracks and crevices of concrete structures, providing a strong and durable bond that can withstand the rigors of regular use.

Both epoxy and polymer resins offer a range of benefits for concrete repairs, and the choice of which to use depends on the specific application and the desired outcome. The addition of filler materials can enhance the mechanical properties of these resins, improving their strength and durability, and making them better suited for use in a variety of concrete repair applications. Ultimately, the choice of which type of resin to use will depend on the specific requirements of the project and the expertise of the repair team.

Read Also: What are Causes of Cracks in Concrete Beams?

Diagnose Structural Damages and Their Repair

1. Retrofit Corroded Structural Member

When corrosion has been detected in concrete structures, a process is adopted to restore the damaged area. The first step involves removing the weak concrete and exposing the reinforcement on all sides. This allows for proper inspection and treatment of the corroded steel.

Next, the rust on the steel is cleaned using wire brushes or sandblasting. Rust removers and rust preventers are then applied to prevent further corrosion of the steel. If necessary, reinforcement can be provided to supplement the rusted steel with anchorage, such as shear connectors.

A tack coat is then applied to create a bond between the old and new concrete using a polymer or epoxy-based bonding material. This ensures that the newly restored area is structurally sound.

To restore the concrete to its original surface level, one of several patching techniques can be used. Polymer-modified mortars are highly effective and can be used with or without guiniting. Additionally, injection of cement slurry or polymer-modified slurry or epoxy can be utilized to fill up pores, internal cracks, or honeycombing.

Finally, a suitable protective coating is applied to the newly restored area to prevent further corrosion and to ensure the longevity of the repair. By following this process, the corroded area of the concrete structure can be effectively restored to its original strength and appearance.

2. Retrofit Severely Damaged Concrete

If the condition of the original concrete is severely compromised and injection grouting is not sufficient to restore the section to its required loading capacity, the recommended solution is to implement Reinforced Concrete Cement (RCC) jacketing of the concrete section. To support the structure during this process, an appropriate supporting system must be put in place.

Before the jacketing process begins, weak concrete must be removed from the section. The surface should be thoroughly cleaned and any rust present on the steel should be removed. This can be achieved by using rust removers and rust preventers.

To reinforce the section, additional steel must be provided all around it. Formwork must also be provided to ensure that the new concrete is of the required thickness and shape.

A polymer-based bonding coat should be applied between the old and new concrete to ensure a strong bond. Finally, concrete of the required thickness, grade, and workability should be placed. The concrete should be admixed with plasticizers to ensure the desired properties are achieved.

Overall, RCC jacketing is an effective solution for severely deteriorated concrete sections. Proper preparation, reinforcement, and application are crucial to ensure the success of the repair.

Read Also: How to Repair Concrete Cracks in Steps

FAQs about Retrofitting of Concrete Structures

Read Also: How to Determine the Severity of Concrete Cracks?