The strength and durability of reinforced concrete (RC) columns can be compromised by four main factors: corrosion of the embedded metal rebar, freeze-thaw deterioration, chemical attack, and localized damage sustained during extreme loading scenarios and natural disasters (e.g., earthquake and flood). As structure ages, concrete spalling can occur exposing the rebar to the elements and depriving it of the alkaline environment, accelerating the reinforcing steel corrosion. When an appropriate repair is not installed in a timely manner on a concrete column, the risk of significant concrete deterioration and progressive collapse can become imminent. As a result, it may require immediate strengthening to prevent further corrosion and concrete degradation and to restore the original structural capacity of the RC. Concrete Columns Strengthening and Repair Techniques For decades researchers have been working on improved methods for strengthening and repairing columns to face the many possible deficiencies. These include a number of strengthening and repair techniques that balance structural requirements with non-structural concerns such as minimizing costs, maintaining functionality and aesthetics, ensuring worker safety, and conducting a repair within a short time frame. An innovative technique, using high-strength, fiber-reinforced polymers (FRP) is quickly becoming recognized as an alternative to traditional retrofitting techniques in construction. The strength-to-weight ratio and adhesion levels, corrosion resistance, ease of handling, and speed of installation are unmatched by traditional repairs like column ties, supplemental vertical bars, or supplemental reinforcing steel. Confining columns with FRP wraps increases ductility while providing excellent shear reinforcement, increasing compressive load capacity, and providing energy redistribution when compared to unconfined RC elements. Traditional Method of Concrete Column Repair Repairs to columns can be divided into two categories: cosmetic repair and structural repair. Cosmetic repairs, when designed correctly, can reduce the rate of further concrete degradation by preventing delamination and stopping reinforcing steel corrosion. Cosmetic Repair Cosmetic or surface repairs are for minor local deterioration, like cracks and pitting of the affected columns as well as concrete delamination. When the rebar is exposed, corrosion will accelerate significantly. As long as the column does not have insufficient load carrying capacity a cosmetic repair can provide a long-term solution. Some examples of cosmetic repairs include mortar replacement, column cage, protective coating application, and composite wrapping. Structural Repair Structural or full repair restores or enhances the integrity of the concrete column and improves the overall strength of the column. If the deterioration does not significantly reduce the cross-section, RC jacketing can successfully be employed. Reinforced Concrete Jacketing Application of RCjacketing is a traditional restoration technique used to strengthen and repair-deficient and damaged concrete columns. It involves covering the existing column with a new layer of concrete, which can be cast around rebar supports or bolted directly to the bottom of the original column. Steel jacketing is also an effective repair option to enhance load and shear capacity while providing added resistance to bending stresses on the column. Although this column repair technique is an efficient way to protect and reinforce a column, in terms of axial load carrying capacity, flexural strength, and ductility, it is expensive and time-consuming. Also, the degree of improvement in ductility is small since the jacketing material is often brittle and does not always bond effectively to the aging concrete. In addition, it changes the cross-sectional area of the column, thereby changing mass and stiffness, which can result in higher seismic demands on the structure. The Rise in Applications of Carbon Fiber-Based Composite Repairs As a result, construction companies are increasingly using composites like carbon fiber and glass-reinforced plastic or epoxy injection to provide external confinement for damaged and weak concrete core when the capacity of the existing column is inadequate. These techniques provide an additional advantage of stopping further degradation of corroded reinforcing steel. Carbon fiber-based composite repairs can also enhance the horizontal load and provide shear reinforcement for concrete structures. Why Use Carbon Fiber for Structural Repair and Reinforcement Carbon Fiber Reinforced Polymers (CFRP) have been a staple of the aerospace industry for decades and are now being successfully applied to many other industries. Carbon fiber-based composites are stronger, lighter, and provide better fatigue resistance than any other typical construction material. CFRPs combine a high strength-to-weight ratio excellent stiffness, ductility, high-temperature tolerance, minimal added weight, and excellent corrosion resistance. They can also be used to repair and prevent cracks, straighten beams, upgrade bridge columns, reinforce walls and piers, enhance seismic resistance, strengthen existing structures after structural modifications, increase lateral load capacity and enhance compressive strength. Column Confinement Flexural Strengthening Crack Repairs Superior Properties of Carbon Fiber Composite High strength to weight ratio Lightweight and corrosion resistance Acid resistance More economical than supplemental column installation Easy and fast to install Reduces costs of transportation and installation Prevents buckling of the column Improves the load-carrying capacity of columns Enhances the flexural strength of the repaired section Repairing Concrete Columns with Carbon Fiber Composite When a damaged or seismically deficient column requires repair, reinforcing the existing column with a fiber-reinforced polymer, like a carbon fiber composite, can restore structural integrity in accordance with DOT regulations. Column restoration is an ideal application for carbon fiber composites because the material is lightweight and extremely strong. The properties of the FRP composite reduce the overall thickness of the repair and minimized any added weight. The hand-applied system will conform perfectly to any size and shape and it will prevent further corrosion to the rebar and cover any bare metal. Repair Procedure Step 1: Prepare the surface When repairing damaged concrete, the first step is surface preparation. It is important to remove any loose material from the column and the footing and ensure a proper bond for the composite repair. Step 2: Replace any missing concrete At Advanced FRP Systems, we generally use polymer cement to replace any missing concrete prior to the installation of the carbon fiber wrap. Concrete is treated with a penetrating primer immediately prior to installation for improved material properties. The primer will increase the adhesion value of the carbon fiber composite and strengthen the concrete itself. Step 3: Saturate carbon fiber composite and wrap it around the column Carbon fiber fabric is saturated and wrapped around the column in discreet bands. Each band has a fixed overlap and the overlaps are staggered with each subsequent band that is installed to improve bond strength. Once the specified number of layers of carbon fiber composite is applied to the concrete column, the material is allowed to cure and a UV stable topcoat is applied. Carbon wrap reinforcement systems, along with an appropriate mortar or polymer cement, provide unmatched strength, resilience, and longevity to a new repair. Depending on the environment, carbon fiber can last more than 50 years without additional repairs. Need Fast and Effective Column Repair? Advanced FRP Systems Can Help Carbon fiber composites are an excellent solution for repairing damaged concrete columns. Carbon fiber offers superior performance against corrosion, resists deterioration, and lasts longer than traditional building elements. It reinforces the structure in a non-invasive way, without changing its interior or exterior look. Advanced FRP Systems offers innovative, customized structural repair and reinforcement solutions for concrete columns, concrete slabs, concrete or masonry walls, piers, docks, seawalls, penstocks, dams, bridges, and more. Our high-quality materials are compliant with many pertinent ISO, DOT, ASME, and API code requirements. Contact us to find the right composite solution for you.