In reinforced concrete structures, the elements such as columns, beams and shear walls built to bear, and transfer loads are called structural elements. Structural elements are expected to safely bear all kinds of vertical and horizontal loads they are exposed to including their own weight and transfer them to the foundation of the building while showing ductile behavior.    
There are 3 common methods preferred for strengthening reinforced concrete structural elements. These methods are FRP system, FRCM system and jacketing. FRP system is a traditional strengthening method, the abbreviation FRP comes from the initials of Fiber-Reinforced Polymer and is also known as CFRP (Carbon Fiber-Reinforced Polymer). The system consists of bonding a technical fabric or plate made of carbon fiber to the reinforced concrete structural element from the outside using epoxy. Another widely used system in addition to the traditional FRP method is the FRCM system. FRCM strengthening system’s name comes from the initials of Fabric-Reinforced Cementitious Matrix, which is a modern and up-to-date method of repair and strengthening. In its simplest form, the strengthening matrix consists of textile reinforcement (also called strengthening textile or technical textile) and a cement or lime-based mortar. The third method, jacketing, consist of anchoring rebars into the structural element with chemical anchors, then enlarging the existing cross-section with new reinforcing bars and concrete.

FRP METHOD APPLICATION PRINCIPLES

FRP strengthening systems are based on the principle that carbon polymer material also bears the stresses on the structural element; thus, increasing the load-bearing capacity and making the structure safer. On the other hand, FRCM strengthening systems are based on the matrix of mortar and textile reinforcement, similar to the way concrete and steel work together in reinforced concrete. In this context, mortar bears the compressive stresses and textile reinforcement bears the tensile stresses. Jacketing strengthening systems are the oldest method of strengthening and are based on increasing the cross-section of the structural element; thus, obtaining a more rigid element that can bear more load. 

Damages may occur in reinforced concrete structural elements due to reasons such as insufficient material strength, poor design of the structural system, structural errors during construction, and wrong calculations during design.

Reinforced concrete structural element damages are considered as primary damage of the system and pose a danger in terms of the safety of the structure. Therefore, the required attention must be shown in repair and strengthening applications.

FRP METHOD RELATED STANDARDS

• T.R. Building Earthquake Code 2019
• T.R. Ministry of Environment and Urbanization Construction Works Technical Specification "Reinforced Concrete Works" 2019
• FIB Bulletin 14 “Externally Bonded FRP Reinforcement for RC Structures”
• FIB Bulletin 35 “Retrofitting of Concrete Structures by Externally Bonded FRPs, with Emphasis on Seismic Applications”
• ACI 440.3R-12 “Guide Test Methods for Fiber-Reinforced Polymers (FRPs) for Reinforcing or Strengthening Concrete Structures”
• JSCE Concrete Engineering Series, No.41 “Recommendation for Upgrading of Concrete Structures with use of Continuous Fiber Sheets”
• CNR-DT 200/2004 “Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Existing Structures – Materials, RC and PC Structures, Masonry Structures”
• ISIS Design Manual No. 4 “Strengthening Reinforced Concrete Structures with Externally—Bonded Fibre Reinforced Polymers (FRPs)”
• CNR-DT 2000 R1 / 2013 “Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Existing Structure”
• ACI 549. 4R-13 “Guide to Design and Construction of Externally Bonded Fabric-Reinforced Cementitious
• Matrix (FRCM) Systems for Repair and Strengthening Concrete and Masonry Structures”
• ICC-ES AC434 10-2018 “Acceptance Criteria for Concrete and Masonry Strengthening Using
• Fabric-Reinforced Cementitious Matrix (FRCM) and Steel Reinforced Grout (SRG) Composites”

FRP METHOD PRODUCTS

FRP APPLICATION STEPS

• The application surface is cleansed of all foreign substances and dust.
• The areas on the reinforced concrete structural element where a repair is required is moistened and repaired with RPM40.
• For the repair, RPM40 is mixed with the specified amount of water for the mixing duration written on the kraft bag, and then applied to the damaged areas to create a flat surface for strengthening.
• EPX Primer A and B components are mixed and prepared in line with the instructions given in the technical data sheet.
• The prepared EPX Primer is applied on the reinforced concrete structural element.
• If the strengthening will be done with Carbon Fabric, EPX FRP, if the strengthening will be done with Carbon Plate, EPX CP A and B components are mixed and prepared in line with the instructions given in their technical data sheets.
• The prepared EPX FRP or EPX CP epoxy is applied on the reinforced concrete structural element.
• Carbon Fabric or Carbon Plate is placed on the epoxy-applied surfaces.
• If the strengthening is done with Carbon Fabric, it is anchored to the reinforced concrete structural element with the selected mechanical anchor.
• After anchoring, EPX FRP is re-applied on Carbon Fabric as the second layer.
• RPM40 or RPM60 is applied as finishing plaster and the strengthening is completed.

FRP METHOD DETAILS TO BE CONSIDERED

• Strengthening should be done directly on the reinforced concrete structural element surface, loose layer on the surface, plaster, ceramic, paint, etc. should be removed. If loose concrete cover or reinforcement corrosion is observed, the loose cover should be removed and the rust on the reinforcement should be mechanically cleaned, then repaired with RPM40.
• Carbon Fabric or Carbon Plate should be tightly placed leaving no gap between the strengthening textile and the reinforced concrete structural element.
• Anchors should be applied in such a way that there are minimum 4 pieces per square meter.
• No extra cement etc. other additives should be added to the mortars, the water ratio should be in accordance with the instructions in the technical data sheet and the mixing equipment must have the mixing speed recommended in the technical data sheet.

    FRCM METHOD PRODUCTS

    FRCM METHOD APPLICATION STEPS

• The application surface is cleansed of all foreign substances and dust, and moistened.
• The selected strengthening mesh is cut to the desired size with appropriate cutting tools.
• RPM40 or RPM60 is mixed with the specified amount of water for the mixing duration written on the kraft bag, and then applied to the reinforced concrete column, beam or shear wall surface with a trowel or spray in approximately 5 mm thickness.
• The strengthening mesh is placed on the mortar surface by hand, and the load distribution plate is placed and anchored to the reinforced concrete structural element with the selected mechanical anchor.
• RPM40 or RPM60 is re-applied with a minimum thickness of 10 mm as the second layer with a minimum thickness of 10 mm fully covering anchors or mesh.

FRCM METHOD DETAILS TO BE CONSIDERED

• Strengthening should be done directly on the reinforced concrete structural element surface, loose layer on the surface, plaster, ceramic, paint, etc. should be removed. If loose concrete cover or reinforcement corrosion is observed, the loose cover should be removed and the rust on the reinforcement should be mechanically cleaned.
• The strengthening mesh should be placed without any gaps and with an overlap of about 20 cm.
• Anchors should be applied in such a way that there are minimum 4 pieces per square meter.
• In order to prevent cracking of the mortar on the surface, the surface should be wetted after 20 minutes once the first curing is completed and the mortar has hardened.
• Where possible, the strengthening mesh should not be finished in the slab plane, it should be finished in adjacent planes by turning and extending 20 cm.
• No extra cement etc. other additives should be added to the mortars, the water ratio should be in accordance with the instructions in the technical data sheet and the mixing equipment must have the mixing speed recommended in the technical data sheet.

JACKETING METHOD Rc  PRODUCTS

JACKETING METHOD APPLICATION STEPS

• The concrete cover of the reinforced concrete structural member to be jacketed is removed and the remaining surface is roughened and cleaned.
• If the column or shear wall strengthening will be continued on the upper floor, the related ceiling slab section’s concrete is removed carefully and cleaned without damaging the existing reinforcing bars. If the strengthening will not be continued on the upper floor, circular holes is drilled on the ceiling slab as one hole per meter for shear walls and four holes at the corners of the column.
• Considering the post-installed rebar diameters and anchorage depth on the project, holes are drilled the reinforced concrete structural member in line with the instructions given in the technical data sheets of V-500 or PE-1000.
• The holes are cleaned and the post-installed reinforcing bars are installed as per the instructions given in the technical data sheets.
• The formwork is installed as per the strengthening project.
• The new reinforcing bars are installed as per the strengthening project.
• To be filled with GROUT, 5 cm of space is left between the shear wall and the beam.
• New concrete is cast from the related places.
• After removing the formwork, the areas where a repair is required is repaired with RPM40.

JACKETING METHOD DETAILS TO BE CONSIDERED

• Strengthening should be done directly on the reinforced concrete structural element surface, loose layer on the surface, plaster, ceramic, paint, etc. should be removed. If loose concrete cover or reinforcement corrosion is observed, the loose cover should be removed and the rust on the reinforcement should be mechanically cleaned.
• The instructions given in the technical data sheets of chemical anchors should be followed in post-installed rebar applications, the curing time stated in the related product ETA should be considered prior to the new reinforcing steel bar installation.
• PE-1000 should be used where diamond drilling is chosen.
• Binding wires should be used during the installation of the reinforcing bars and there should be a minimum of 4 pieces of concrete cover spacers per square meter.
• The formworks should be cleaned prior to the installation and formwork oil should be applied.
• Before the formwork is closed, it should be checked if there is any foreign material in the formwork.
• Where a self-leveling concrete is not used, proper vibrations should be applied, and concrete should be cast in minimum 3 pours.
• After the formwork is removed, the concrete should be properly cured.
• No extra cement etc. other additives should be added to the mortars, the water ratio should be in accordance with the instructions in the technical data sheet and the mixing equipment must have the mixing speed recommended in the technical data sheet.