FRP Rebar and Bridge Decks: Where Composites Are Heading

In short: Steel corrosion from de-icing salt and seawater is one of the main reasons concrete bridges wear out. Composites attack the problem in two ways. Glass FRP (GFRP) rebar replaces steel bars inside concrete; it now has a US building code, ACI CODE-440.11-22, and AASHTO bridge design specifications, both tied to the ASTM D7957 bar standard. FRP bridge decks replace heavy concrete or rusting steel grate decks; FHWA reports more than 100 FRP decks and structures in service, and a federal project built and tested a deck weighing about 17 pounds per square foot. Both have real limits: GFRP bars are less stiff than steel and do not yield, and FRP decks need careful detailing of joints and wearing surfaces. FIBROVX does not make rebar or bridge decks as standard products; they are custom / available on request.

How this guide fits with our others

This guide looks at structural composites in bridges and civil works. For the pultrusion process behind most of these products, see what is pultrusion and our pultruded profiles guide. Our pair article, RF-transparent FRP enclosures for 5G and telecom, covers another frontier use of composites in infrastructure. Other sectors are on our industries page and emerging industries page.

Why infrastructure is turning to composites

A paper presenting the second edition of the AASHTO GFRP bridge specifications notes that corrosion-resistant GFRP bars have become a viable technology for bridges, particularly in cold regions where de-icing salts are used and in coastal areas. FHWA's composite deck report adds that many existing bridges used open steel grating decks, whose long-term durability has been a maintenance problem because of corrosion and fatigue cracking. An open deck also lets salt, water and debris reach the steel beneath.

The FDOT GFRP training course lists the advantages of GFRP bars over steel:

• High strength-to-weight ratio along the bar
• Corrosion resistance
• Electromagnetic neutrality
• Good fatigue endurance
• Low thermal and electrical conductivity
• Light weight

GFRP rebar: the codes are now in place

For a long time, designers had guides but no code. That has changed:

• AASHTO, first edition (2009): covered the design of GFRP-reinforced concrete bridge decks and open-post railings.
• AASHTO, second edition (approved June 28, 2018): expanded to a full bridge design guide specification, including girders, bent caps, footings and piles. It refers to ASTM D7957-17 for bar materials, and only vinyl ester or epoxy GFRP round bars are allowed. Its layout follows the AASHTO steel-reinforced bridge specifications, so the language is familiar to bridge engineers.
• ACI CODE-440.11-22 (effective September 2, 2022): the building code for structural concrete reinforced with GFRP bars. It covers cast-in-place, precast, nonprestressed and composite construction, and requires bars that meet ASTM D7957-22. Topics include strength, serviceability, durability, load factors, deflection limits, development and splicing, inspection and evaluation of existing structures.

The AASHTO overview paper explains why national documents matter: state and local agencies rely on them so that federal funding eligibility is not put at risk.

How GFRP bars differ from steel

GFRP is not a drop-in swap. The FDOT training course gives typical values:

What this means in design:

• Lower stiffness. GFRP-reinforced members deflect more, so serviceability often controls the design, as FDOT's design presentation notes.
• No yielding. GFRP is elastic to failure. The FDOT course states it has no ductility and is not used where plastic hinges must form, as in seismic designs.
• Weak in compression and shear. Compressive strength of the bar is ignored in design, and shear and dowel action are resin dominated.
• Creep rupture. Constant tension can cause the fibers to fail after time, so sustained stress is limited.
• Environment. Design strength is reduced by an environmental factor; for glass bars in concrete exposed to earth or weather, FDOT's example uses 0.7.
• Bends are factory made. FDOT standard plans state pultruded bars cannot be field formed or modified. Bends can cut tensile strength at the bend by up to about 40% per ASTM D7957. FDOT suggests limiting hooked and bent bars to 15 ft long and closed shapes such as stirrups to 5 ft in each direction.
• Fire and heat. The training course lists susceptibility to fire and smoke and loss of properties at high temperature as cons.

Practical tips if you are considering GFRP rebar

• Name the code and bar standard. State ACI CODE-440.11-22 or the AASHTO GFRP specification, and the ASTM D7957 edition the bars must meet.
• Keep bent bar types few. FDOT advises using fewer bent bar types, lapped with straight bars of varying length, to cut fabrication cost.
• Complete the bar list early. Because bars cannot be changed on site, the reinforcing bar list in the plans must be final before ordering.
• Plan for inspection. ACI 440.11 includes field inspection and testing, so build these into the contract.
• Check deflection first. With a modulus about a quarter of steel's, run serviceability checks early rather than as a final step.

FRP bridge decks: light, durable, detail-sensitive

FHWA's Highways for LIFE project, Composite Bridge Decking, set out to show that a high-quality FRP deck meeting AASHTO service requirements could be made economically. Its reports give useful numbers.

Weight. FHWA's preliminary report compares approximate deck weights, excluding wearing surface:

• Reinforced concrete: 100–120 psf
• Filled steel grate: 70–100 psf
• Exodermic: 50–75 psf
• Open steel grate: 17–55 psf
• Timber: 22–30 psf
• FRP: 12–25 psf

The finished proof-of-concept deck, built with pultruded tubes on stringers 24 inches apart, weighed about 17 psf without grout. That matters for movable bridges, historic bridges and structures not designed for heavy concrete decks.

Design driver. The project found a large safety factor for strength. The design was driven by stiffness under local deformation, to protect the wearing surface, not by rider comfort. Grout in selected cells could raise stiffness by about 40% for wider stringer spacing. The preliminary report kept live load stresses near 20% of ultimate and dead load below 10% to guard against creep rupture, with global deflection typically set at L/800.

Fatigue. In laboratory testing, a panel showed no stiffness loss after 1 million load cycles of 1 to 14 kips, and test wearing surfaces showed no visible cracks.

Fire. Direct fire burned resin off the exposed underside of a panel, even with fire-resistant resin, but damage stayed local and strength dropped slowly. After 20 minutes of a 1,500 °F (about 815 °C) fire under the deck, the top surface was not much above room temperature, and the panel was judged still serviceable.

A real installation. The project installed its proof-of-concept deck on a 40-foot-long bridge in Allegany County, New York, in August 2012. The deck went down as prefabricated panels lifted by crane, with epoxy grout and transverse bars in the field joints and a two-course wearing surface on top. The bridge was then instrumented and load tested with trucks, and the results agreed well with the finite element model. FHWA notes that prefabricated panels can be installed quickly, which reduces traffic disruption and improves work zone safety.

Joints and surfaces. The project also found weak points to manage:

• The bond between cementitious grout and FRP was not satisfactory without extra measures beyond sanding.
• Thermal cycling may debond grout from FRP tubes, and further testing was suggested.
• A paper on the project reports an unexpected opening of the centerline field joint after an exceptionally cold winter, showing the need for detailed thermal analysis.
• The two-course wearing surface looked promising in the lab, but long-term field performance is the real test.

Why FRP decks are not yet everywhere

FHWA's final report is candid about why the more than 100 FRP decks and structures in service have not led to widespread use:

• Proprietary systems. Most decks have been proprietary, which bridge owners generally do not like, and public purchasing rules written to foster competition can hinder adoption.
• Wearing surfaces. There have been troubles with bonded wearing surfaces cracking, spalling and delaminating.
• Initial cost. Because material cost is higher than conventional options, FHWA expects use may focus on cases where rapid installation offsets traffic control costs, or where light weight matters most, such as movable, deteriorated or historic structures.

FHWA also states that total life-cycle cost is competitive because the material resists corrosion and fatigue. That is the core case for composites in infrastructure: pay more at the start to spend less on repair later.

Where composites are heading

Based on these sources, the direction is clear, even if the pace varies by agency:

• From guides to codes. With ACI 440.11 and the AASHTO second edition, GFRP rebar can be specified through a normal code path instead of one-off approvals.
• From decks to whole bridges. AASHTO's scope grew from decks and railings to girders, caps, footings and piles.
• Light decks for special cases. FRP decks suit movable, historic and weight-limited bridges where concrete is too heavy.
• Testing protocols. The FHWA project proposed qualification from coupon tests up to full panels, fire, joints, railing posts and field load tests.

Honest limits

• Not for every structure. Lack of ductility rules GFRP out where plastic hinges are needed, such as seismic designs.
• Serviceability governs. Expect more reinforcement or deeper sections to control deflection and cracking.
• Plan bends early. No field bending, so bar lists must be right before fabrication.
• Deck details decide success. Joints, connections and wearing surfaces need careful design and field follow-up.
• First cost. FHWA reported the deck performed well but cost was not driven down as much as hoped.

Where FIBROVX fits

FIBROVX makes pultruded profiles, grating and access products in our grating and profiles collection, used for walkways, handrails and platforms around infrastructure. For the steel vs FRP trade-off, see FRP profiles vs steel and aluminum. We do not make GFRP rebar or vehicle bridge decks as standard products. Pultruded bars, deck tubes and bridge-related parts are custom / available on request, built to a project specification and qualified by the testing the engineer of record requires. We make no certification claims for these items.

FAQ

Is there a code for GFRP rebar?

Yes. ACI CODE-440.11-22 for buildings and the AASHTO LRFD Bridge Design Guide Specifications for GFRP-Reinforced Concrete, second edition, for bridges.

What standard do GFRP bars meet?

ASTM D7957. ACI 440.11-22 references D7957-22; the AASHTO second edition references D7957-17.

Can GFRP bars be bent on site?

No. Bends are made in the factory, and strength at the bend can drop by up to about 40%.

How light is an FRP bridge deck?

FHWA lists about 12–25 psf without wearing surface, versus 100–120 psf for reinforced concrete.

Can GFRP be used in seismic zones?

The FDOT training course says no plastic hinges form, so it is not used where they are needed.

Why are FRP decks used on movable bridges?

Weight. An FRP deck at roughly 12–25 psf is far lighter than concrete, which matters for movable, historic and weight-limited bridges.

Do you sell FRP rebar or bridge decks?

Not as standard products. They are custom / available on request, with no certification claims.

Related: FRP Structural Design Basics: Deflection, Creep and Safety Factors; FRP Design Manuals and Load Tables: What They Contain and How to Use Them; Custom FRP Manufacturing: Sizes, Resins, Colors, Molds and OEM Explained.

Sources

• ACI CODE-440.11-22, product page: https://www.concrete.org/store/productdetail.aspx?ItemID=44011U22&Language=English&Units=US_Units
• ACI CODE-440.11-22, front matter (effective date): https://www.concrete.org/Portals/0/Files/PDF/FRP-440.11.22-Chap22.pdf
• Overview of AASHTO LRFD Bridge Design Guide Specifications for GFRP Reinforced Concrete (FDOT): https://fdotwww.blob.core.windows.net/sitefinity/docs/default-source/structures/innovation/frp/fib_331-gfrpspecx.pdf
• Bridge Design Guide Specifications for GFRP-RC, IBC 2018 (FDOT): https://fdotwww.blob.core.windows.net/sitefinity/docs/default-source/structures/innovation/frp/ibc18-w4-2.pdf
• FDOT, AASHTO GFRP Reinforced Concrete Design Training Course, 2020: https://fdotwww.blob.core.windows.net/sitefinity/docs/default-source/structures/innovation/fdot-2020-gfrp-pc-training/1-intro_gfrp-rc_08102020.pdf?sfvrsn=a901a271_2
• FDOT, FRP Reinforced Concrete Design, 2017: https://fdotwww.blob.core.windows.net/sitefinity/docs/default-source/structures/innovation/2017---rick-vallier---frp-reinforced-concrete---rev01.pdf?sfvrsn=f179d0e7_2
• FDOT Standard Plans Index 415-010, Bar Bending Details (FRP), 2026: https://fdotwww.blob.core.windows.net/sitefinity/docs/default-source/design/standardplans/2026/spi/spi-415-010.pdf?sfvrsn=45b39350_1
• FHWA, Composite Bridge Decking, Preliminary Design Report: https://www.fhwa.dot.gov/hfl/partnerships/composite_bridge/preliminary_report.pdf
• FHWA, Composite Bridge Decking, Final Project Report (HIF-13-029), full PDF: https://www.fhwa.dot.gov/hfl/partnerships/composite_bridge/hif13029/hif13029.pdf
• FHWA, Composite Bridge Decking, Final Project Report, conclusions: https://www.fhwa.dot.gov/hfl/partnerships/composite_bridge/hif13029/chap05.cfm
• FHWA, Composite Bridge Decking, Phase I Design Report (fatigue tests): https://www.fhwa.dot.gov/hfl/partnerships/composite_bridge/hif13030/chap12.cfm
• O'Connor, Testing FRP Bridge Decks, ASC 31st Technical Conference: https://www.dpi-proceedings.com/index.php/asc31/article/view/3259