Carbon Fibre Strengthening in UK Construction: An Interview with Mihai Chelmus
The landscape of structural engineering is constantly evolving, and one innovative material is making a significant impact: Carbon Fibre Reinforced Polymer (CFRP). To delve deeper into this remarkable technology, we sat down with Mihai Chelmus, Operations Manager at Swantest, to explore the intricacies and benefits of CFRP in strengthening structures.
If you have questions or design/specification queries for the carbon fibre reinforcement polymer structural strengthening solutions, feel free to reach out to Mihai Chelmus at mihai.chelmus@swantest.co.uk or 07342281981.
CFRP: A Game-Changer in Structural Reinforcement
Carbon Fibre Reinforced Polymer (CFRP) is a composite material composed of carbon fibres embedded within a polymer resin matrix. This unique combination creates a material that boasts exceptional strength while remaining remarkably lightweight.
The Advantages of CFRP Strengthening
✔ Enhanced Structural Capacity: CFRP can significantly increase the load-bearing capacity of existing structures, offering a solution for buildings requiring additional support.
✔ Minimal Disruption: Compared to traditional strengthening methods, CFRP installation is often less disruptive, minimising downtime and construction costs.
✔ Lightweight Solution: The inherent lightness of CFRP adds minimal weight to the structure, making it ideal for projects where weight is a concern.
✔ Versatility of Applications: CFRP can be used for various strengthening applications, including beams, columns, slabs and walls.
✔ Durable and Long-lasting: CFRP is resistant to corrosion and offers a long-lasting solution for structural reinforcement.
Additional Benefits of CFRP
✔ Quick Installation: CFRP can be installed quickly, reducing the time required for strengthening projects.
✔ Non-Intrusive: The application of CFRP does not significantly alter the appearance of the structure, preserving its aesthetic value.
✔ Adaptability: CFRP can be easily adapted to complex structural geometries, providing a flexible solution for various design challenges.
✔ Eco-Friendly: The use of CFRP can contribute to sustainable construction practices by extending the life of existing structures and reducing the need for new materials.
Interview with Mihai Chelmus
Q: What is the design life of CFRP structural strengthening systems?
MC: The design life of CFRP structural strengthening systems is detailed in the Concrete Society Technical Report 55: Design guidance for strengthening concrete structures using fibre composite materials (TR-55). Both epoxy materials and carbon fibres are inert, meaning their longevity greatly depends on the condition of the concrete to which the CFRP is bonded. It is essential to address and prevent any issues that could impact the strengthened area and the broader structure. Factors such as water penetration, corrosion, and surface cracking can affect the local concrete strength or the bond strength of the adhesive.
Q: How do you ensure that the CFRP strengthening is acting as one with the existing structure?
MC: Ensuring that CFRP strengthening functions integrally with the existing structure involves several key factors:
✔ Correct Positioning: The wrap or plate must be positioned so that the fibres are placed into tension by the new loads. This is primarily a design consideration but can also be influenced by site workmanship.
✔ Proper Bonding: The CFRP must be fully bonded to the substrate material. For reinforced concrete structures, this involves adequate surface repair and preparation to remove contaminants and ensure a clean bonding surface. For column confinement, corners must be rounded to a consistent radius of >20 mm.
✔ Adequate Anchorage: Proper anchorage must be considered in the design, with mechanical anchorages correctly specified and installed.
✔ Load Transfer: Testing the concrete's strength in tension ensures it can transfer loads to the fibres effectively. Surface flatness must also be maintained for effective load transfer.
✔ Correct Adhesive Usage: Using the right adhesive in the correct amount ensures strong, complete bonding without voids.
✔ Environmental Conditions: The work must be carried out under the right temperature, humidity, and moisture conditions to ensure the adhesive performs as expected.
✔ Proper Overlaps: For wrapping applications, overlaps must be greater than 200 mm and distributed around the column for adjacent wraps.
Q: What are the typical approaches to provide fire protection to CFRP strengthening?
MC: While CFRP often isn't required to achieve a structure's fire resistance due to accidental load scenarios, fire protection can be provided using specialist fire protection mortars and fire boarding techniques. These methods can enhance both the Fire Resistance and Reaction to Fire of the structure and the CFRP, though they come with limitations. Fire-boarding techniques can also be effective.
Q: Do you have Environmental Product Declarations (EPD) for structural strengthening products, and how does the GWP compare to equivalent steel reinforcement?
MC: We offer a wide array of EPDs and LEEDv4 Attestations for our materials, including resins, adhesives, and epoxy-based repair materials used in CFRP structural strengthening. Although we have not conducted direct comparison studies between CFRP and steel plate bonding, CFRP's lower weight generally results in a lower overall contribution to global warming potential (GWP) despite its higher material energy intensity. Additionally, the energy intensity of CFRP plate installation is often lower due to fewer operatives and trades on site, reduced logistic demands, and no need for specialized preparation.
Q: Does the CFRP strengthening require fire protection to be applied after installation?
MC: If fire protection is required, it is always applied after the CFRP strengthening systems have been installed and the adhesive or resin has cured. Fire protection mortar, like Sikacrete-213 F, requires broadcasting suitable kiln-dried quartz sand to achieve the necessary mechanical bond with the mortar.
Q: What is NSM reinforcement?
MC: NSM, or Near Surface Mounted reinforcement, involves installing CFRP bars and rods in channels within the cover concrete, keeping the strengthening system 'hidden' within the structure. This is particularly advantageous in scenarios where accidental damage risk is high. NSM bars provide excellent anchorage and are widely used for flexural strengthening against negative moments over supports. They are also used to strengthen timber structures where hidden installations are important.
Q: Can you provide a comparison of costs for reinforced concrete jacketing and steel plate bonding vs. CFRP strengthening based on your experience?
MC: While it's challenging to state comparative costs with confidence due to site-specific factors, CFRP generally offers significant cost savings through reduced program duration, fewer trades and labour, and less temporary works and material use. For example, CFRP wrapping a single column may cost similarly to installing a reinforced concrete jacket, but the wrapping method takes significantly less time to reach full strength.
Q: What is the impact of penetrations through the CFRP?
MC: Drilling through CFRP creates stress concentrations that can significantly weaken the composite section. The design phase should consider any required fixtures to minimise damage to the installed materials.
CFRP is revolutionising the way we approach structural strengthening in the UK construction industry. Its exceptional strength, lightweight nature, and versatility offer a compelling solution for extending the lifespan and improving the performance of existing structures. As CFRP technology continues to develop, we can expect even more innovative applications to emerge in the years to come.
