An FRP, or fiber-reinforced polymer, is made up of a fiber and a resin. Three types of fibers are used in most FRPs: carbon, fiberglass or Aramid (Kevlar®). Fibers provide the strength and stiffness to an FRP and can also influence other physical properties, such as durability, the coefficient of thermal expansion and density.
Polymers can be one of many resin types, like epoxy, polyester or PVC. The polymer holds the fibers in alignment, protects the fibers from damage, transfers stress from fiber to fiber, influences the durability of the FRP and chemically resistant and helps to create a usable FRP form like a plate, bar or grid.
Fibers and polymers must be chemically compatible because not all fiber and polymer combinations result in a usable FRP material. Carbon fibers are manufactured to be compatible with epoxy resins. Its use with other resin types would typically result in sub-optimal performance.
FRPs are categorized as wet lay-up or pre-cured systems. Wet lay-up is the most common FRP form used in the United States. In this process, dry fabrics made with continuous fibers are wet out with a saturating resin in the field and adhered to or wrapped around an existing concrete member. Heavier weight fabrics may need to be pre-saturated to ensure adequate impregnation of the fibers. Wet lay-up is used for strengthening all types of members because it can easily conform to the shape of a structure and wrap around members, like columns.
Learn more about FRP installations in our white paper, “The Fundamentals of FRP Strengthening.”
FRPs are structurally very high strength and stiff but lightweight. The lightweight fabrics and easy installation contribute to overall cost savings on most projects by reducing the labor and equipment requirements. The thin and corrosion-resistant material makes for durable and aesthetically pleasing repairs that are unnoticeable to the community once the material has been painted.
FRPs are used to strengthen or retrofit a wide range of structures. DOTs around the country commonly use FRPs to reinforce the following types of members:
Decks and Deck Overhangs
Learn more about these structural repairs in our white paper, “The Fundamentals of FRP Strengthening.”
There are many methods that inspectors can use to determine if the FRP repair is acceptable. Visually, the inspector can verify if the contractor is following the correct installation procedure, verify the ply orientation and verify that the correct number of layers is applied.
There are many inspection techniques employed on FRP projects, but it is important to specify these based on if the project is contact-critical or bond critical and if it is a structural or non-structural application.
Read more about FRP inspections in our white paper, “The Fundamentals of FRP Strengthening.”