Characteristics and Behaviors of Fiber Reinforced Polymers

Table of Contents

Fiber Reinforced Polymers

Fiber Reinforced Polymers: Prior to designing structures of fiber reinforced polymers (FRP), it is critical to understand the mechanical characteristics and behaviors of composite materials with glass (GFRP), aramid (AFRP), carbon (CFRP), basalt (BFRP), and fibers against steel reinforcement bars.

FRP materials are becoming a more suitable substitute for steel reinforcement in reinforced concrete buildings, such as on-site concrete and pre- cast elements.

FRP strengthening is also beneficial for masonry systems.

Their application as primary reinforcement and for structural stabilization is being increasingly defined by civil engineers in both the public and private sectors.

Types of Fiber Reinforced Polymers (Source)

Glass-FRP (GFRP)

Glass fibers are the most often used reinforcing fiber in FRPs. The most often used fiber is e-glass. It has excellent electrical insulating characteristics, a high resistance to heat, and is the least expensive. S-Glass fibers are more resistant to heat and have a tensile strength approximately one-third that of E-glass fibers. While the specialized AR-glass fibers are resilient to the alkaline conditions present in concrete, they are far more expensive.

Aramid- FRP (AFRP)

Aramid fibers (also called aromatic polyamide fibers) are extremely strong, have a high modulus of elasticity, and weigh 40% less compared to glass fibers. Since aramid fibers are more expensive than basalt and glass fibers, they are used in less structural applications. Additionally, since aramid fibers absorb moisture, cautious storing and preparation are needed before the fibers are impregnated with a polymeric matrix.

Carbon- FRP (CFRP)

Carbon fibers have an extremely high tensile strength and modulus of elasticity. Carbon fibers with a high modulus of elasticity have a comparable elastic modulus to steel. CFR made of very high modulus carbon fibers is common in the aerospace sector due to its superior strength-to-weight ratio compared to other FRPs. In the infrastructure sector, high strength, ordinary modulus fibers have been used in conjunction with CFRPs.

Basalt- FRP (BFRP)

Basalt fibers have a better tensile strength than E-glass fibers but a lower tensile strength than S-glass fibers; however, their cost is comparable to E-glass fibers. It is significantly more resistant to alkalis in concrete than E- and S-glass.

FRP Design Characteristics

The following are the key physical properties taken into account when designing:

Maximum tensile strength
Tensile elastic modulus
Fracture strain, a material’s pressure at fracture.

Due to the linear-elastic behaviour of FRPs, these properties are interrelated as described by Hooke’s law, which equals Maximum tensile strength/ Fracture strain.

Type	Yield Strength (MPa)	Tensile Strength (MPa)	Elastic Modulus (GPa)	Fracture Strain %
Steel	(275-515)	Not applicable	(200)	Not applicable
GFRP	Not applicable	(485-1610)	(36-52)	1.2-3.2
BFRP	Not applicable	(1040-1655)	(46-60)	1.5-3.0
AFRP	Not applicable	(1720-2540)	(42-126)	2-4.5
CFRP	Not applicable	(1720-3690)	(125-585)	0.6-2

Notes:

Although steel has a high ultimate tensile strength, it is rarely used during design.
The values for the different FRPs are approximate and are dependent on a standard fiber volume fraction of 0.49 to 0.71.
ACI 440.6 requires that reinforcement bars made of glass fiber or carbon fiber have a minimum tensile elastic modulus of 40 GPa and 125 GPA, respectively.