The Future of Lightweight and High-Strength Materials: Fiber Reinforced Polymer
Fiber-reinforced polymers (FRPs) are ideal construction materials in that they are lightweight, high-strength, and durable. For many decades conventional steel-reinforced concrete has been used extensively, and its performance characteristics and limitations are well known. Due to concerns of steel reinforcement over corrosion from environmental chemical processes such as oxidation, relatively high self-weight, and the associated maintenance costs, alternative materials have emerged. FRP is a lightweight material with a high strength-to-weight ratio, excellent fatigue resistance, and superior durability, which has successfully emerged as a promising substitute for steel reinforcement in a wide range of structural applications.
FRPs are not a single type of material but a family of composite materials formed by embedding high-strength reinforcing fibers within a polymer matrix. The reinforcing fibers provide the main mechanical properties and stiffness, while the polymer matrix acts as a binder that holds the fibers together, protects them from environmental and chemical degradation, and provides for an efficient load transfer among the fibers. The reinforcing fiber types, such as glass fibers, carbon fibers, and aramid fibers, are the most commonly used in concrete-related applications. FRPs can be applied to concrete structures in a variety of ways depending upon the structural requirements. One of the most popular methods is the externally bonded FRP sheets/wraps for the repair and strengthening of the existing structures. Alternatively, FRP materials can be used as internal reinforcement, such as FRP reinforcing bars, grids, or fiber-based reinforcement systems, where they serve as a permanent structural component.
Compared to the tensile strength of steel reinforcement (approximately 550 MPa), carbon fiber reinforced polymer (CFRP) can achieve a tensile strength up to 3,000 MPa [Eng et al. 2019]. Therefore, FRPs are often used as temporary repair and strengthening materials, especially in such cases as the underside of bridges and the intrados of tunnels. Such structures are often difficult to inspect, and damage may not be detected until visible cracking or severe deterioration, including partial collapse, occurs.
Due to their high strength and good mechanical performance, FRPs are often used as temporary repair materials for such damaged structures. But the widespread use of existing FRPs in long-term applications has not materialized so far due to a number of physical limitations. Their lower strength at high temperature, the risk of sudden brittle failure because of their high tensile strength, and their dependence on proper installation and bonding quality have raised concerns about long-term use. The research on externally bonded FRP strengthening systems is increasingly directed at the direct integration of fibers into concrete matrices to overcome the limitations of conventional reinforced concrete.
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