What Is FRP? Fiber Reinforced Polymer Explained

What is FRP?

FRP stands for fiber reinforced polymer, also called fiber reinforced plastic. It is a composite: strong, stiff fibers locked in a polymer resin. Neither part does the job alone. Loose fibers can’t carry compression or share load, and resin on its own is weak. Together they make a thin, light layer that is stronger than steel in tension and does not rust.

For design, the American Concrete Institute defines an FRP system as the fibers and resins in the laminate, the resins that bond it to the concrete, and any protective coatings (ACI PRC-440.2-23, 2023).

In construction, FRP is mostly used to repair and strengthen what is already built. It comes as dry fabric that is saturated with resin on site, as factory-made laminates and panels, and as structural pipe. You will see it called CFRP when the fiber is carbon and GFRP when it is glass.

What is FRP made of?

Every FRP system combines one or more fibers with one resin. The choice of each sets the strength, stiffness, cost and where the product can go.

The fibers

• Carbon: the highest strength and stiffness. Common for bending and shear strengthening of beams, slabs and girders.
• Glass: lower cost and non-conductive. Fiberglass is the everyday name for glass FRP.
• Aramid (Kevlar) and basalt: less common in repair. The 2023 edition of the ACI design guide added basalt FRP to the commercially available systems it covers.

The resin

The resin, usually epoxy for structural repair, has two jobs inside the composite. It distributes the load among all the fibers, and it protects them from abrasion, moisture and other environmental attack. In a repair it is also the glue between the FRP and the beam, column or pipe.

Why fiber direction and fiber content matter

FRP is anisotropic: its properties change with direction. A unidirectional fabric is very strong along its fibers and much weaker across them. That is a feature, not a flaw. The engineer runs the fibers where the load runs, around a column for confinement or along the bottom of a beam for bending, and puts strength exactly where it is needed.

Is FRP stronger than steel?

In tension, yes. Once the epoxy cures, FRP reaches about two to three times the tensile strength of steel at a fraction of the weight, as Prof. Mo Ehsani noted in Concrete International in 2025. QuakeWrap® carbon fabrics saturated with QuakeBond™ 300SR cure to laminates of 129 to 179 ksi, and glass fabrics to 24.3 to 70.9 ksi, per the product data sheets.

FRP behaves differently from steel too. It stays elastic until it ruptures, with no yield plateau, and it is much weaker across its fibers than along them. That is why it is used as tension reinforcement, as shear wraps and as confinement, and why its design follows its own guide.

Carbon FRP vs. glass FRP: which is better?

Neither is better everywhere. Carbon is stronger and stiffer, glass costs less and does not conduct electricity, and many QuakeWrap® designs use both, choosing the fiber that suits each member.

Strength ranges are for QuakeWrap® fabrics saturated with QuakeBond™ 300SR, from the product data sheets. Check the current product data sheet before design.

Conductivity matters more than people expect. On a utility job near live equipment, glass was chosen for its dielectric properties. Read how in repairing corroded substation structures without an outage.

How does FRP compare with steel and concrete repairs?

FRP adds strength with almost no added size or weight, where steel plates and concrete jackets add bulk, weight and downtime. The conventional ways to strengthen concrete, as the ACI guide lists them, are bonded steel plates, steel jackets, enlarging the section with new concrete, and external post-tensioning (ACI PRC-440.2-23).

How does FRP strengthen a structure?

FRP strengthens a member in one of four ways, depending on where it is bonded and which way its fibers run.

1. Flexure (bending)FRP bonded to the tension face of a beam or slab acts as added tension reinforcement and raises bending capacity. See beam strengthening.
2. ShearWraps and U-wraps on the sides of a member resist diagonal cracking.
3. ConfinementFully wrapping a column or pile confines the concrete, which raises axial capacity and ductility. See column strengthening.
4. Corrosion barrierEncasing a member shuts off the moisture and oxygen that feed corrosion, which sharply slows the corrosion of the steel and concrete inside.

The corrosion barrier is easy to overlook. Paint protects steel until it cracks and peels a few years later. FRP is like a paint reinforced with fibers: it seals the member and keeps sealing it. That matters because corrosion is expensive. The 2016 NACE IMPACT study put its global cost at about US$2.5 trillion a year, 3.4% of world GDP, and estimated that existing corrosion control practices could save 15% to 35% of it.

What types of FRP repair systems are there?

FRP comes in several forms, from fabric saturated on site to factory-made laminates, panels and pipe. Each one solves a different access or surface problem.

Where did FRP repair come from?

FRP structural repair began in the late 1980s, when Prof. Mo Ehsani and his associates at the University of Arizona pioneered the wet layup method. Each later product generation solved a limit of the one before it.

1. Wet layup fabrics (1990). Carbon or glass fabric saturated with epoxy in the field. By the next day it reaches two to three times the tensile strength of steel. The method appeared in Concrete International in March 1990 and has since been used on thousands of projects.
2. Factory-made laminates (2010). Wet layup has three limits: the fabric cannot follow the sharp corners of a steel H-pile, the surface must be patched smooth first, and it cannot go on underwater without a cofferdam. Laminates pressed under heat and pressure to about 0.04 in. thick remove most of that. Thousands of piles have been repaired with them since 2012.
3. SPiRe® and SPiRe®+ panels (2018). SPiRe® launched in 2018 as a stay-in-place FRP form. SPiRe®+ panels, 3 ft wide with a 0.2 in. wall, replace three products at once: formwork, reinforcing steel and waterproofing.

Play video: S2E8: The Evolution of FRP Repairs with Prof. Mo

Plays from YouTube

Where is FRP used in construction?

FRP is used wherever a structure needs more strength, or has lost strength, and adding steel or concrete would be too heavy, too slow or too disruptive. QuakeWrap® FRP has been used on more than 1,000 projects in 28 countries.

• Beams and girders: bending and shear strengthening of concrete and steel beams.
• Columns: confinement and repair of corroded concrete and steel columns.
• Piles: concrete, steel and timber piles, above and below water.
• Seawalls and bulkheads: corroded sheet pile and concrete walls.
• Pipelines and culverts: pressure pipes, sewers, penstocks and culverts, often without digging.
• Seismic retrofit: columns, walls and tilt-up buildings strengthened for earthquakes.
• Tanks, chimneys and blast hardening.

Owners turn to FRP to restore members weakened by corrosion, age or impact, to add capacity for heavier loads or a new use, to correct construction or design errors such as low-strength concrete, and to meet current seismic codes. Because it bonds to the outside, a wall, beam or slab can be strengthened without enlarging it.

What are the limitations of FRP?

FRP is not right for every job. Externally bonded FRP has limited fire resistance, its resin needs a coating to resist UV, bonded systems depend on proper surface preparation, and FRP and concrete expand differently with temperature.

Results also depend on design by a licensed engineer and installation by trained crews. QuakeWrap® supports the engineer of record with specifications and sample details.

Does FRP cost more than steel or concrete?

FRP materials cost more per pound, but the finished repair often costs less. It is light, installs quickly with small crews and light equipment, often avoids taking the structure out of service, and needs little maintenance. The ACI guide puts it this way: FRP often extends the life of existing infrastructure at a fraction of the monetary and environmental cost of replacing it (ACI PRC-440.2-23).

For worked numbers on real repairs, see steel column repair cost, an economical way to strengthen concrete columns and the PileMedic® cost estimator.

Is there a design standard for FRP?

Yes. The main US reference is the American Concrete Institute’s guide for externally bonded FRP systems, now ACI PRC-440.2-23, published in November 2023. It supersedes ACI 440.2R-17, which many earlier designs, including some on this site, cite. ACI also publishes a specification for unidirectional carbon and glass wet layup systems (ACI 440.8).

The guide is not a code on its own: the engineer of record makes and certifies the design calculations. QuakeWrap® FRP systems have also been evaluated by IAPMO UES (ER-828), and fabrics with QuakeBond™ 300SR have been listed to NSF/ANSI/CAN 61 for drinking water pipes and tanks. Current reports are on our test results and approvals page.

FRP frequently asked questions

Sources

1. ACI Committee 440, Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures: Guide (ACI PRC-440.2-23), American Concrete Institute, November 2023.
2. NACE International (now AMPP), IMPACT: International Measures of Prevention, Application, and Economics of Corrosion Technologies, 2016.
3. Mo Ehsani, Evolution of FRP Products for Concrete Repair, Concrete International, April 2025.
4. H. Saadatmanesh and M. R. Ehsani, Fiber Composite Plates Can Strengthen Beams, Concrete International, March 1990.
5. QuakeWrap, Inc., product data sheets for U27C and U27G fabrics with QuakeBond™ 300SR.
6. QuakeWrap, Inc., What Is FRP? (introduction), 2013 to 2023 editions.