Application guide
GFRP rebar applications
Seven places engineers replace steel reinforcement with glass fiber reinforced polymer bars, what changes in the detailing, how each market approves the bar, and which public projects to read before you specify. Reference projects are attributed to the producers that supplied them.
- Applications
- 7 segments
- Why GFRP
- No corrosion · nonmagnetic · cuttable
- Design basis
- ACI 440.11 · AASHTO GFRP-2 · CSA S6
Last updated
Seawalls, piles, caps and wharves
Chloride-driven corrosion of steel is the failure mode in marine concrete: the rust expands, cracks the cover and the repair cycle starts within 15 to 25 years. A glass-fiber bar does not corrode electrochemically, so the exposure that drives seawall design stops being a reinforcement problem and becomes a concrete and detailing problem.
What changes in the detailing
- Cover is set by bond splitting and fire, not by corrosion; the designer may reduce it where the code allows, which is a design option rather than an automatic allowance.
- Cages are a quarter of the weight of steel, which matters for auger-cast and secant piles handled over water; some owners needed a variance before contractors could push GFRP cages into fresh concrete.
- Transverse thermal expansion of a GFRP bar is three to eight times its longitudinal value, so cover and spacing checks for splitting belong in the design record.
Reference projects
- Typical sizes
- Ø10–Ø25 mm (No. 3–No. 8) straight bars, factory-formed U-bars and cage stirrups.
- Approval route by market
- Middle East owners such as Saudi Aramco now mandate GFRP in corrosion-risk concrete and buy by the million metres through pre-qualified suppliers. Florida DOT runs its own producer list and shipment testing. Private owners in the United States, Australia and Asia accept a third-party ASTM D7957 or ISO 10406-1 test package reviewed by the engineer of record.
- What to send
- Exposure class and design life, the governing specification, bar schedule for piles, caps and panels, and whether cages are assembled on site or supplied formed.
Precast panels, tunnel segments and architectural concrete
A precaster controls placement, cover and curing, so the arguments for GFRP are production arguments: lighter cages and mesh handled by one person, no rust staining on exposed architectural faces, reduced cover where the design allows and no spalling risk on thin elements. Repeat schedules suit factory-cut lengths and welded-pattern mesh.
What changes in the detailing
- ACI CODE-440.11-22 covers precast non-prestressed members; prestressing with GFRP is outside its scope and outside EN 1992-1-1 Annex R.
- Mesh is outside ASTM D7957, so sheet properties and joint strength need their own test scope agreed before the first lot.
- Thin elements benefit most, but deflection and crack width govern at a quarter of steel's stiffness; the design is redone, not converted bar for bar.
Reference projects
- Typical sizes
- Ø6–Ø16 mm bars cut to repeat lengths; mesh with Ø6–Ø10 rods at 100–200 mm centres; factory stirrups for segments.
- Approval route by market
- Precasters qualify one supplier and grade against their own quality system, usually starting with a sample lot and full test scope. In Europe an ETA under EAD 260023-00-0301 is the CE route; in the United States an ICC-ES report under AC454 supports building-code acceptance. Neither is held by an importer, so the project engineer reviews third-party test reports instead.
- What to send
- Element drawings, repeat quantities per month, mesh pattern and sheet size, surface finish requirements and the test scope your quality plan needs.
Slabs on grade, pavements, pool shells and ICF walls
This is the largest-volume use of GFRP rebar. Flatwork is reinforced for shrinkage and temperature rather than flexure, so the low modulus matters less, while the weight saving speeds placement and the absence of rust staining and corrosion makes the slab tolerant of thin cover and wet service. Pool builders adopt it for chlorinated water and clean finishes.
What changes in the detailing
- Research cited by producers shows a No. 3 GFRP bar controlling shrinkage cracking like a No. 4 steel bar; the engineer confirms the substitution for the slab in question.
- Light bars float: tie them to chairs so the mat does not lift during the pour.
- Pavement dowels are a separate product tested to ASTM D8444; GFRP dowels need a 20 to 30% larger diameter than steel for the same joint stiffness.
Reference projects
- Typical sizes
- Ø10–Ø16 mm (No. 3–No. 5) in 6 m, 12 m or 20 ft lengths; Ø6–Ø10 mm coils or mesh for light slabs.
- Approval route by market
- Distributors and contractors buy a stable size mix without a design approval. In the United States, residential and commercial permits accept bars with an ICC-ES report under AC521 or AC454, or an engineer's letter based on ASTM D7957 test data. Outside North America the engineer of record specifies the standard and the test package.
- What to send
- Slab area and thickness, bar size and spacing or the steel schedule to be converted, cut lengths, delivery rhythm and whether the order is for a project or for stock.
Bridge decks, approach slabs and barrier walls
De-icing salts and traffic disruption make a corrosion-free deck worth a higher first cost. A Minnesota DOT scenario put a GFRP deck at $42 per square foot against $36 for epoxy-coated steel, and the 100-year present value at $67 against $87 because the GFRP deck carried no repair cycle. Decks, barriers and approach slabs are the mature structural use of GFRP.
What changes in the detailing
- Design follows AASHTO GFRP-2 (2018) in the United States and CSA S6 Section 16 in Canada; strength reduction and sustained-stress limits differ from steel.
- Owners specify high-modulus grades: CSA S807 Grade III (60 GPa) in Ontario, 7,500 to 8,700 ksi minimum modulus at Texas and Ohio DOT.
- Every shipment to a Florida DOT project is sampled and tested at the contractor's expense: six straight and five bent bars per size.
Reference projects
- Typical sizes
- Ø16–Ø32 mm (No. 5–No. 10) straight bars with factory-formed barrier stirrups and hooks.
- Approval route by market
- In the United States and Canada this work runs through state producer lists, Buy America rules effective for GFRP since October 2025, and CSA S807 Grade III requirements. An imported bar is not a candidate for that work. Outside North America, bridge owners specify project by project with a third-party test package and lot testing.
- What to send
- Owner specification and design code, modulus grade required, bar schedule with bends, lot testing requirements and the destination country.
MRI suites, electrified rail slabs and electrical facilities
A GFRP bar is nonmagnetic and electrically insulating. Imaging rooms, substations, track slabs with signalling currents and laboratories with sensitive instruments need a reinforcement mat that does not distort fields or carry stray current. Concrete near MRI suites has used GFRP since the 1980s.
What changes in the detailing
- The whole mat must stay nonmetallic: chairs, spacers, ties and couplers included.
- The equipment supplier's exclusion zone, not the structural engineer, usually defines where the nonmetallic reinforcement starts and ends.
- Track-slab research shows GFRP transverse bars preserving track-circuit current where steel would short it.
Reference projects
- Typical sizes
- Ø8–Ø20 mm bars and mesh with plastic or composite accessories.
- Approval route by market
- Specified by the equipment supplier and the structural engineer together; no approval regime beyond the project's own test package in most markets. Schöck Combar holds a German DIBt approval used for rail and research buildings in Europe.
- What to send
- The exclusion zone drawing, bar sizes and spacing, accessory requirements and the electrical or magnetic acceptance criteria the equipment supplier has issued.
TBM soft-eyes, diaphragm walls and temporary works
A tunnel boring machine cannot cut through a steel-reinforced wall, so the breakthrough zone of a shaft or diaphragm wall is reinforced with GFRP that the cutterhead grinds away. The same cuttability serves roadheader faces in mining and temporary works that will be excavated later.
What changes in the detailing
- Soft-eyes are engineered packages: the designer sizes the GFRP zone for construction loads and the breakthrough sequence, and specifies the splice to the surrounding steel cage.
- A polyester matrix is acceptable only for temporary use; permanent works need vinyl ester and alkali-resistance data.
- Lower stiffness has led designers to thicken walls at the soft-eye; the Channel Tunnel Rail Link grew its wall from 1.2 to 1.5 m for this reason.
Reference projects
- Typical sizes
- Ø20–Ø32 mm cages with factory-formed U-bars and composite or steel-to-FRP couplers.
- Approval route by market
- Led by the contractor's designer and bought as a package; Dextra reports more than 500 soft-eyes supplied since the Bangkok MRT in 1996. An importer competes on the bar supply within the designer's package, with test data for every size and the coupler system agreed.
- What to send
- The soft-eye zone drawing, bar sizes and cage geometry, coupler or splice detail, whether the works are temporary or permanent, and the construction program.
Water, wastewater and chemical plant concrete
Chlorination tanks, channels, sumps and slabs in wet or chemically aggressive service would otherwise need coated or stainless steel. Life-cycle studies of chlorination tanks put GFRP's net present cost about 40% below black steel over 100 years with a breakeven around 35 years.
What changes in the detailing
- Chemical, concentration and temperature determine the resin and the test exposure; ask for alkali and, where relevant, acid exposure data for the offered grade.
- Crack-width limits for watertightness often govern the bar area at GFRP's modulus.
- Nonmetallic reinforcement also removes stray-current corrosion near cathodic-protection systems and electrical equipment.
Reference projects
- Typical sizes
- Ø10–Ø25 mm bars and mesh for walls, slabs and channels.
- Approval route by market
- Industrial owners and EPC contractors accept supplier qualification data with a project-specific exposure review; no listing regime applies in most markets.
- What to send
- Process chemistry and temperature, exposure classes, crack-width or watertightness criteria, element drawings and the bar schedule.
GFRP rebar application questions
What is GFRP rebar used for?
Concrete where steel's corrosion, magnetism, conductivity or uncuttability is the problem: seawalls and marine structures, bridge decks and barriers exposed to de-icing salt, slabs, pavements and pools, precast panels and tunnel segments, MRI suites and rail slabs, TBM soft-eyes, and water or chemical plant concrete.
Where is fiberglass rebar not allowed?
ACI CODE-440.11-22 excludes GFRP from seismic-force-resisting systems in higher seismic design categories and applies only where a fire-resistance rating is not required of the member; prestressing with GFRP is outside the code. Owners add their own limits. The engineer of record decides element by element.
Can an imported GFRP bar be used on a US DOT bridge?
In practice no. State DOTs buy from producer lists maintained through plant audits, Buy America rules have applied to GFRP since October 2025, and several states require a higher modulus than ASTM D7957's minimum. Private and commercial work, and projects outside North America, are specified project by project against a third-party test package.
Which application has the most GFRP volume?
By linear metres, slabs, pavements and channel linings in the Middle East and US flatwork; by single order size, marine and flood channels such as the Jizan channel in Saudi Arabia. Bridge decks are the mature structural use and TBM soft-eyes the oldest engineered niche.
What should I send to get an application reviewed?
The exposure or function that drives the choice, the governing specification and design code, element drawings or a bar schedule, the documents your engineer requires and the destination. A technical review before the schedule is complete is a normal first step.
Bring the exposure, the code and the drawings
Send the application, the governing specification and a bar schedule or element drawings. We confirm the bar forms, sizes and evidence available before you fix the design. We reply within one business day.