Carbon and Organic-Based Fibers
The evolution of fiber-reinforced plastic (FRP) as reinforcement in concrete began in the 1960s to solve the corrosion problem associated with steel-reinforced concrete in highway bridges and structures . This is a class of materials defined as a polymer matrix, whether thermosetting (e. g., polyester, vinyl ester, epoxy, phenolic) or thermoplastic (e. g., nylon, PET) reinforced by fibers (e. g., aramid, carbon, glass). Each of the fibers considered suitable for use in structural engineering has specific elongation and stress-strain behavior. Composite reinforcing bars have more recently been used for construction of highway bridges and it appears that the largest market will be in the transportation industry. Figure 2 shows an example of repairing a small bridge by preparing a network of FRP beams and then casting a construction concrete. The engineering benefits of these fibers include the inhibition of plastic and shrinkage cracking (by increasing the tensile strain capacity of plastic concrete), reducing permeability, and providing greater impact capacity, and reinforcing shotcrete.
Fig. 2 Setting a FRP network for casting a construction concrete in the repair of a bridge (Courtesy of D. Gremmel, Hughes Brothers)
Carbon fiber-reinforced plastic (CFRP) in grid form has demonstrated potential as a reinforcing material in lightweight concrete. A high tensile capacity allows the grid to work efficiently with compressive strength in bending. Additionally, carbon fiber may act as thermal insulator. It allows a reinforced mold for production when used in grid form. However, a CFRP grid is an expensive and brittle material, and the grid form can melt under a fire accident.