Retrofitting Using FRP
FRP systems for strengthening and repairing have been in use since the mid 1990’s. They are being applied on beams, columns, and slabs of buildings and bridges to increase the strength and extend their service life, even after they have been severely damaged due to excess loading, environmental effects including earthquakes, or impacts. This method is widely accepted and has proven to be effective in improving capacity of reinforced concrete elements.
WHAT IS FRP
FRP stands for Fiber Reinforced Polymers or Plastic, and it is a composite material made mainly of a polymer matrix reinforced with fibers. The fibers are usually glass (in fiberglass or GFRP), carbon (in CFRP), aramid, or basalt, and the polymer is usually an epoxy, vinylester, or polyester thermosetting plastic. The role of the fibers is to mechanically enhance the strength and elasticity of the plastic composite.
For structural applications, carbon and glass fibers are mostly used in the plastic composite, because of their excellent tensile and elastic properties. On the field, rolls of fabric made of carbon or glass fibers are saturated with a special epoxy resin from one side and then bonded to the exterior of a concrete surface. The material cures quickly and can reach double the strengths of steel in 24 hours. FRP composites can also be prefabricated in a manufacturing facility in which the material is modified to create different shapes that can be used for strengthening applications, such as rods, bars and plates. FRP plates or layers have a typical thickness of only few millimeters, and come in variable shapes and dimensions as per project specifications. Once applied, FRP can be painted, or coated with stucco.
FRP AT WORK
There are many possibilities of strengthening and retrofitting concrete structures using FRP. Mainly suitable for concrete beams, walls, slabs and columns, but can also be used to strengthen cut-out openings in slabs or walls. Depending on the structural design load and project requirements, FRP systems are used to enhance the following:
Shear strengthening, and
Column confinement and ductility improvement
The first applications with CFRP plate system were carried out in Switzerland during the beginning of the 1990s, where a concrete bridge was strengthened due to an accident that broke the pre-stressing cables. Since then there have been numerous applications of this technology worldwide, from strengthening bridge decks and beams to retrofitting old and decaying historical structures.
When comparing with conventional repair and strengthening systems, FRP has the following advantages:
Fast and clean to install
Reach desired strength faster
Lightweight and easy to transport material
Material is flexible and can conform to any geometry
High strength-to-weight ratio and excellent resistance to corrosion
Resins used in the composite are non-hazardous and odorless making the system ideal for work in occupied buildings
Speed and low construction costs
FRP also serves as a waterproofing membrane
Doesn’t require a large work/setup area
When considering all factors, such as installation costs, time frame allocated for completing the project, time needed to reach the desired designed load, the space available to perform the work, and the life service maintenance costs of the repair system, FRP has proven to be more economical and more durable than conventional repair methods.
Erhard, Gunter. “Designing with Plastics.” Trans. Martin Thompson. Munich: Hanser Publishers, 2006.
Concrete Construction. “Repairing and Strengthening Masonry Walls with FRPs”. https://www.concreteconstruction.net/products/repairing-and-strengthening-masonry-walls-with-frps_o [viewed on December 19, 2018]
The Constructor. “Cost of Reinforced Concrete FRP Strengthening System and other Methods” https://theconstructor.org/practical-guide/rcc-frp-strengthening-system-methods/21014/[viewed on December 19, 2018].
Wikipedia. “Fibre-reinforced plastic”. https://en.wikipedia.org/wiki/Fibre-reinforced_plastic [viewed on December 19, 2018].
Structure Magazine. “Strengthening of Concrete Structures Using FRP Composites”.https://www.structuremag.org/?p=8643viewed on December 19, 2018].
Ola Enochsson. “CFRP Strengthening of Concrete Slabs, with and without Openings.” Licentiate Thesis. Lulea University of Technology. 2005.
Images Credits: https://phil-are-go.blogspot.com/2013/07/motorola-hi-fi-in-fiber-glass-carbon.html https://afzir.com/en/products/frp-thixotropic-epoxy-adhesive/ https://ctech-llc.com/en/applications/structural-elements/slabs/ https://ctech-llc.com/en/applications/structural-elements/beams/ https://ctech-llc.com/en/applications/structural-elements/columns/ [viewed on December 19, 2018].