Glass fiber reinforced concrete (GFRC) is a fine mortar reinforced with chopped alkali-resistant (AR) glass fibers, glass holding at least 16 % zirconium dioxide (ZrO2) by mass (EAD 260002-00-0301), which lets 10 to 20 mm (0.39 to 0.79 in) sections carry flexural load. The UK and Europe call it glassfibre reinforced concrete (GRC), and fiberglass for concrete means this alkali-resistant fibre, never ordinary E-glass.
AR glass fiber is dosed into the batch like steel, polypropylene and basalt fibers, and its niche is the thin section that bends. Fibers sit with admixtures and pozzolans among the concrete additives that change a mix from inside.
GFRC is placed by premix or spray-up at EAD reference contents of 3 % and 5 % AR glass by mass of total GRC. ASTM C1666/C1666M-08(2023), ASTM C1116/C1116M-23 Type II and ANSI/PCI 128-24 govern in the US; EN 15422:2008 and EAD 260002-00-0301 in Europe.
Fiber acceptance rests on zirconia by XRF and a strand-in-cement strength above 250 MPa (36,260 psi); handling follows the product SDS and the US limits for fibrous glass dust.
The table summarizes AR glass fiber for GFRC.
| Attribute | Value |
|---|---|
| Material | AR glass with at least 16 % ZrO2 by mass of glass, by XRF (EAD 260002-00-0301) |
| Forms | Continuous roving (spray-up); chopped strands of 6 to 25 mm (0.24 to 0.98 in) (premix) |
| Processes | Premix; spray-up |
| Reference fiber content | 3 % (premix) and 5 % (spray-up) by mass of total GRC (EAD assessment contents, not design doses) |
| Section thickness | 10 to 20 mm (0.39 to 0.79 in) |
| Standards | ASTM C1666/C1666M-08(2023); ASTM C1116/C1116M-23 Type II; EAD 260002-00-0301; EN 15422:2008 |
| Hazard line | See the product SDS |
Each value is traced to its source: standards and codes to their issuing body, product values to the data sheet named with them, prices to the dated source beside them (methodology and fact-checking).
What Is Glass Fiber Reinforced Concrete?#
Glass fiber reinforced concrete is a cement-based composite in which chopped AR glass fibers, placed by premix or by spray-up, carry tension in thin sections that bend.
ASTM C1116/C1116M-23 lists glass fiber-reinforced concrete with AR glass fibers as Type II and excludes spray-up thin-section GFRC (Subcommittee C27.40).
The same specification places steel (Type I), synthetic (Type III) and cellulose fibers (Type IV) beside glass; basalt fits no type. All families are compared on the page about fiber-reinforced concrete.
What makes a glass fiber alkali resistant?#
A glass fiber is alkali resistant when the glass contains at least 16 % zirconium dioxide (ZrO2) by mass, determined by X-ray fluorescence (XRF), the requirement of EAD 260002-00-0301. Zirconia is a component of the glass melt, not a substance added to the concrete.
Ordinary E-glass is not alkali resistant: the alkaline pore solution of the cement paste dissolves it. Zirconium dioxide (CAS 1314-23-4, EC 215-227-2) is the oxide that gives AR glass its resistance to that solution.
Regional names: GFRC, GRC and glassfibre reinforced concrete#
Four names describe the same composite by region: GFRC, GRC, glassfibre reinforced concrete and glassfibre reinforced cement. US specifiers write GFRC and AR glass fiber; the UK and the EU use GRC or the two glassfibre names, and Indian practice uses GRC. Suppliers list the fiber itself as AR glass, alkali-resistant glass fiber or zirconia glass fiber.
How Do AR Glass Fibers Reinforce Thin GFRC Sections?#
AR glass fibers reinforce GFRC as chopped strands bonded in a mortar, where zirconia lets the glass resist the alkaline pore solution and the strands keep bridging cracks in the thin section. In a section this thin, the chopped strands are the only reinforcement.
The placement process sets the fiber orientation and the fiber content. Spray-up places long chopped strands in a two-dimensional random orientation at a higher fiber content. Premix blends shorter fibers into a mortar that is then cast, vibrated, pressed or sprayed; the European reference contents differ by process, 5 % for spray-up against 3 % for premix by mass of total GRC.
What Do AR Glass Fibers Change in the Composite?#
AR glass fibers add a stiff, strong reinforcement to the mortar: glass fiber has a modulus of about 80 GPa (11.6 million psi) and a tensile strength of about 2,500 MPa (362,600 psi). Its density is about 2.7 g/cm³ (169 lb/ft³), literature values from the Sika Fiber Reinforced Concrete Handbook, against 1 to 8 GPa for polypropylene and 210 GPa for steel. Inside cement, EAD 260002-00-0301 requires a strand-in-cement strength above 250 N/mm² (250 MPa, or 36,260 psi), and in the fresh mix fibers reduce workability (ACI FAQ). The table compares glass with three other fibers on the same literature basis.
| Fiber | Modulus | Tensile strength | Density | Page |
|---|---|---|---|---|
| AR glass | 80 GPa (11.6 million psi) | 2,500 MPa (362,600 psi) | 2.7 g/cm³ (169 lb/ft³) | this page |
| Steel | 210 GPa (30.5 million psi) | 400 to 2,500 MPa (58,000 to 362,600 psi) | 7.8 g/cm³ (487 lb/ft³) | steel fibers for concrete |
| Polypropylene | 1 to 8 GPa (0.15 to 1.16 million psi) | 165 to 600 MPa (23,900 to 87,000 psi) | 0.90 to 0.91 g/cm³ (56.2 to 56.8 lb/ft³) | polypropylene microfibers in concrete |
| PVA | 30 GPa (4.35 million psi) | 880 to 1,600 MPa (127,600 to 232,100 psi) | 1.31 g/cm³ (81.8 lb/ft³) | PVA fibers |
Literature values (Sika Fiber Reinforced Concrete Handbook); fiber material properties, not composite properties of GFRC.
GFRC Fiber Content and Batching: Premix vs Spray-Up#
GFRC fiber content is stated by mass of the total composite: EAD 260002-00-0301 assesses AR glass at 3 % by mass of total GRC for premix and 5 % for spray-up. The basis, fiber over fiber plus matrix, travels with every figure, because a percentage of the matrix or of the cement gives a different number for the same batch.
Fiber content by process and its basis#
The 3 % and 5 % figures are reference contents, the fiber contents at which the EAD assesses the effect of AR glass on bending strength, and never design doses. The worked example below, calculated from those contents, converts them to fiber per batch of matrix.
- Inputs: matrix mass 100 kg (220.5 lb); reference content 3 % (premix) or 5 % (spray-up) by mass of total GRC, where total GRC equals fiber plus matrix.
- Premix: fiber = 100 × 0.03 / 0.97 = 3.09 kg (6.82 lb) per 100 kg of matrix.
- Spray-up: fiber = 100 × 0.05 / 0.95 = 5.26 kg (11.60 lb) per 100 kg of matrix.
Adding 3 kg of fiber to 100 kg of matrix gives 2.9 % by mass of total GRC, not 3 %: the error an unstated basis produces. Design contents come from the project specification and trial batches.
Premix: chopped strands blended last#
Premix blends chopped AR glass strands of 6 to 25 mm (0.24 to 0.98 in) into the mortar last, at low shear. ACI PRC-549.3-22 (published 2022) covers premix that is cast, sprayed, pressed, pultruded or extruded, with materials, proportions and the influence of fiber content.
Fibers reduce workability, and the ACI answer is to restore it with a water reducer or high-range water reducer and to add the fibers at a set point in the sequence, never to add water. High-range water reducers, also called superplasticizers, return the flow without extra water; their dosage is covered under superplasticizers.
Spray-up: roving chopped at the gun#
Spray-up feeds continuous AR glass roving to the gun, which chops it into strands that enter the mortar spray. The strands land in a two-dimensional random orientation, and the process runs at the higher reference content of 5 % by mass of total GRC in EAD 260002-00-0301.
ASTM C1116/C1116M-23 excludes spray-up thin-section GFRC (Subcommittee C27.40), so spray-up work is specified through the panel route: ANSI/PCI 128-24 for GFRC panels, the document that IBC 2024 Section 1903.2 references.
What goes into a GFRC mix?#
Four components define a GFRC mix at specification level, listed below in the order a specifier states them.
- AR glass fiber at the process content, set by the project specification and trial batches.
- Fine mortar matrix: the cement-based mortar that bonds the chopped strands.
- Metakaolin: a pozzolan used in GFRC (ACI PRC-549.3-22), described under metakaolin in concrete.
- Acrylic polymer curing aid: a polymer used in GFRC matrices (ACI PRC-549.3-22).
A high-range water reducer restores the workability the fibers take away. ACI PRC-549.3-22 covers premix materials and proportions, and a plant sets its own proportions by trial batches, as in any concrete mix design, worked through under concrete mix design.
Which Standards Cover AR Glass Fibers and GFRC?#
Seven documents govern AR glass fibers and GFRC: ASTM C1666/C1666M-08(2023), ASTM C1116/C1116M-23, ANSI/PCI 128-24, PCI MNL-130-09, ACI PRC-549.3-22, EN 15422:2008 and EAD 260002-00-0301. The table sets them side by side with edition, status and the requirement each one carries.
| Region | Document (edition, status) | Covers | Requirement value | Page |
|---|---|---|---|---|
| US | ASTM C1666/C1666M-08(2023), active (updated 2023-05-25) | AR glass fiber for GFRC (spray-up and premix) and FRC | Minimum zirconia content (value not stated here), physical properties, conformance tests | |
| US | ASTM C1116/C1116M-23, active (updated 2023-08-23) | Type II glass fiber-reinforced concrete | Spray-up thin-section GFRC excluded; uniformly mixed, free of fiber balls | ASTM C1116 fiber-reinforced concrete specification |
| US | ANSI/PCI 128-24 (2nd ed.), current | GFRC panels | Referenced by IBC 2024 Section 1903.2 | |
| US | PCI MNL-130-09 (2nd ed.) | Plant quality control | Plant QC manual | |
| US | ACI PRC-549.3-22, published 2022 | GFRC premix report | Materials, mixture proportions, fiber content influence | |
| EU | EAD 260002-00-0301 (March 2016, OJEU 2017) | ETA route for AR glass fibers with ZrO2 | ZrO2 at least 16 % by XRF; strand-in-cement above 250 MPa; 1.5 MPa at CMOD 0.5 mm, 1.0 MPa at CMOD 3.5 mm | |
| EU | EN 15422:2008, no newer edition listed (2026-10-23) | Glassfibres for GRC | Specification; outside EN 14889 | EN 14889 steel and polymer fibres |
US: fiber specification, Type II and the panel specification#
ASTM C1666/C1666M-08(2023), active and last updated on 2023-05-25, specifies AR glass fiber for GFRC by spray-up and premix and for fiber-reinforced concrete. It sets a minimum zirconia content, physical properties and conformance tests, and does not cover coatings and lubricants. ASTM C1116/C1116M-23 (updated 2023-08-23) classes AR glass fiber-reinforced concrete as Type II, delivered uniformly mixed and free of fiber balls, made to ASTM C94/C94M-26c or the volumetric-batching specification, as modified.
Panels follow ANSI/PCI 128-24 (2nd edition), which replaces ANSI/PCI 128-19. IBC 2024 Section 1903.2 requires GFRC and its materials to comply with PCI 128, as adopted for example in TWIA 2024. Plant quality control runs to PCI MNL-130-09 (2nd edition).
Europe: the glassfibre specification and the ETA route#
AR glass fibers sit outside EN 14889 in Europe and follow EN 15422:2008 or a European Technical Assessment under EAD 260002-00-0301. EN 14889-1:2006 covers steel fibers and EN 14889-2:2006 polymer fibers, both current editions. EN 15422:2008, "Precast concrete products - Specification of glassfibres for reinforcement of mortars and concretes", is the product specification. The EAD 260002-00-0301 of March 2016, published in the OJEU in 2017, is the route to an ETA for AR glass fibers containing ZrO2 for use in concrete, a product no harmonized standard covers. Its concrete-use thresholds equal those of a structural declaration under EN 14889 steel and polymer fibres.
How Does GFRC Interact With Cement, Pozzolans and Admixtures?#
AR glass fibers depend on the cement matrix around them: the glass-matrix interaction lowers GFRC strength and ductility with age, and plain E-glass is not alkali resistant. ACI PRC-549.3-22 names two matrix measures used in GFRC: metakaolin and acrylic polymer curing aids.
Admixtures act on the fresh mortar, not on the glass: a water reducer or high-range water reducer restores the flow that fibers remove (ACI FAQ).
The dispersant choice follows the cement, pozzolan and polymer of the matrix, so it is confirmed in trial batches. Fibers lower the workability of concrete and mortar alike, as set out under workability of concrete.
When Is GFRC the Right Choice?#
GFRC is the right choice where a concrete element must be thin, 10 to 20 mm (0.39 to 0.79 in), and still carry flexural load, as in architectural panels made to ANSI/PCI 128-24.
Slabs-on-ground are a different case: macro fibers replace welded wire reinforcement or temperature steel there by equivalent residual strength (ACI PRC-544.4-18). The table matches five applications to the fiber or route and the evidence behind each.
| Application | What the fiber must do | Fiber or route | Evidence |
|---|---|---|---|
| Architectural panels and cladding | Carry flexure in a 10 to 20 mm (0.39 to 0.79 in) section | AR glass, spray-up or premix; ANSI/PCI 128-24 | IBC 2024 Section 1903.2 references PCI 128 |
| Cast or pressed elements (admixtures for precast concrete) | Reinforce a premix that is cast, vibrated or pressed | AR glass premix | ACI PRC-549.3-22 |
| Thin non-structural elements | Reinforce a section without bars | AR glass at the process content, 3 % or 5 % by mass of total GRC | EAD 260002-00-0301 reference contents |
| Slabs-on-ground | Residual strength replacing mesh | macro-synthetic fibers or steel | ACI PRC-544.4-18; FRCA Fibers in Practice 8 |
| Plastic-shrinkage control in ordinary concrete | Crack control in fresh concrete | Polypropylene microfibers | Low-modulus microfiber, 1 to 8 GPa (literature) |
When is AR glass the wrong fiber?#
AR glass is the wrong fiber for three jobs: residual-strength design of ground slabs, shear reinforcement credit and the replacement of structural bars. Ground slabs use steel or macro-synthetic fibers. ACI 318-19(22) Table 9.6.3.1 gives fibers in lieu of minimum shear reinforcement only to deformed steel fibers conforming to ASTM A820. Structural bars in girders, columns, suspended decks and cantilevers cannot be replaced by fibers (FRCA Fibers in Practice 9). Plastic-shrinkage crack control in ordinary concrete is a microfiber task, covered under plastic shrinkage cracking.
Which Tests Prove AR Glass Fibers and GFRC?#
Three levels of test prove AR glass fibers and GFRC: the fiber itself, the fiber in concrete and the fresh fiber-reinforced mix. At fiber level, EAD 260002-00-0301 requires at least 16 % ZrO2 by XRF and a strand-in-cement strength above 250 MPa (36,260 psi). For use in concrete, the EAD declares the fiber dosage that gives a residual flexural strength of at least 1.5 MPa (218 psi) at a crack mouth opening displacement (CMOD) of 0.5 mm (0.020 in) and 1.0 MPa (145 psi) at 3.5 mm (0.138 in). These equal the EN 14889 structural declaration, measured on the EN 14651:2005+A1:2007 notched beam of 150 x 150 x 550 mm (5.9 x 5.9 x 21.7 in) on a 500 mm (19.7 in) span, and define a declared dosage, never a design dosage. In the US, ASTM C1609/C1609M-24 is the active residual-strength test, on 100 x 100 x 350 mm (3.9 x 3.9 x 13.8 in) beams over 300 mm (11.8 in) or 150 x 150 x 500 mm (5.9 x 5.9 x 19.7 in) beams over 450 mm (17.7 in), reading residual strengths at L/600 and L/150.
The table lists each test level with its requirement and the document that sets it.
| Level | Test or requirement | Value | Document |
|---|---|---|---|
| Fiber | ZrO2 content by XRF | At least 16 % by mass of glass | EAD 260002-00-0301 |
| Fiber | Strand-in-cement strength | Above 250 MPa (36,260 psi) | EAD 260002-00-0301 |
| Fiber in concrete | Residual flexural strength | At least 1.5 MPa (218 psi) at CMOD 0.5 mm; 1.0 MPa (145 psi) at CMOD 3.5 mm | EAD 260002-00-0301; EN 14651:2005+A1:2007 beam |
| Fresh FRC | Uniformity | Uniformly mixed, free of fiber balls | ASTM C1116/C1116M-23 |
| US flexural test | Residual strength at L/600 and L/150 | Beam test, no acceptance value set here | ASTM C1609 flexural performance |
| Panels | Plant quality control | Plant QC program | PCI MNL-130-09 |
How Durable Is GFRC Over Time?#
GFRC loses part of its strength and ductility as it ages, through the interaction between the glass and the cement matrix, so GFRC designs use aged properties. A facade panel is therefore designed on aged properties and specified to ANSI/PCI 128-24.
Zirconia is the reason AR glass survives the alkaline pore solution at all, and ordinary E-glass dissolves in it. ACI PRC-549.3-22 names metakaolin and acrylic polymer curing aids among the materials used in GFRC matrices.
GFRC Safety and Handling#
AR glass fibers are handled under the product SDS: the fibers cause mechanical skin and eye irritation, and US exposure limits apply to fibrous glass dust. The NIOSH Pocket Guide gives a REL of 3 fibers/cm³ TWA (fibers 3.5 µm or less in diameter, 10 µm or longer) and 5 mg/m³ total; the OSHA PEL is 15 mg/m³ total and 5 mg/m³ respirable. Portland cement (CAS 65997-15-1) carries its own line: No Annex VI entry; ECHA C&L notified classification: H315, H317, H318, H335. Fresh concrete is caustic and can cause chemical burns (ASTM C494/C494M caveat). Cutting or grinding GFRC can release respirable crystalline silica: OSHA PEL 50 µg/m³ 8-hour TWA, action level 25 µg/m³ (29 CFR 1926.1153, effective 2016-06-23); EU limit 0.1 mg/m³ (Directive (EU) 2017/2398). The table lists each material with its line or limit.
| Material | Hazard line or limit | Source (checked) |
|---|---|---|
| AR glass fiber | See the product SDS (mechanical skin and eye irritation from fibers) | Product SDS |
| Fibrous glass dust | NIOSH REL TWA 3 fibers/cm³ and 5 mg/m³ total; OSHA PEL TWA 15 mg/m³ total, 5 mg/m³ respirable | NIOSH Pocket Guide |
| Portland cement (CAS 65997-15-1) | No Annex VI entry; ECHA C&L notified classification: H315, H317, H318, H335 | ECHA C&L (2026-10-23) |
| Fresh mix | Caustic, can cause chemical burns | ASTM C494/C494M-24 caveat |
| Respirable crystalline silica (cutting, grinding) | OSHA PEL 50 µg/m³ 8-hour TWA, action level 25 µg/m³; EU limit 0.1 mg/m³ | 29 CFR 1926.1153; Directive (EU) 2017/2398 |
What Drives the Cost of AR Glass Fiber?#
No dated public price for AR glass fiber is on record, so a GFRC fiber quote is compared on four factors: fiber material, fiber content, minimum order quantity and freight. Content follows the process, spray-up running higher than premix, so offers are compared per kg of fiber at the same process content.
AR Glass Fiber Grades and Sourcing#
AR glass fiber is sold as continuous roving for spray-up and as chopped strands of 6 to 25 mm (0.24 to 0.98 in) for premix, and buyers compare grades on zirconia content, strand length and documents. A data sheet states one product's values: HPM AR (Pioneer Fibre) declares ZrO2 of at least 16.5 % in chopped strands of 6 or 12 mm (0.24 or 0.47 in), a typical product value, not a standard requirement. Declared grades are compared as set out for concrete admixture manufacturers and suppliers.
A zirconia figure needs its method and document: the EAD sets 16 % by XRF, while ASTM C1666/C1666M-08(2023) conformance is a separate claim.
The five items below belong in every AR glass fiber inquiry.
- Zirconia declaration with its test method (XRF).
- Conformance to ASTM C1666/C1666M-08(2023) or a European Technical Assessment under EAD 260002-00-0301.
- Strand form and length: continuous roving or chopped strands, in mm (in).
- Sizing suited to premix or spray-up.
- Safety data sheet (SDS) for the fiber.
Where AR Glass Fits Among Concrete Fibers#
AR glass is the fiber for thin GFRC sections, while macro fibers replace mesh in slabs by residual strength and basalt fits no ASTM C1116 type. AR glass mesh used in renders and exterior insulation systems is a construction-chemical product and is not covered here. GFRC panels as finished products, their design and installation are not covered here; the page covers the fiber, the mix and the standards. An example basalt fiber shows no zirconia, as compared under basalt fibers in concrete.
GFRC FAQs#
What does GFRC stand for?#
GFRC stands for glass fiber reinforced concrete, written GRC (glassfibre reinforced concrete or cement) in the UK, Europe and India.
Is GFRC the same as GRC?#
Yes: GFRC and GRC name the same composite of AR glass fibers in a cement mortar; the US uses GFRC and the UK, Europe and India use GRC.
Can ordinary fiberglass be used in concrete?#
No: ordinary E-glass fiberglass is not alkali resistant and dissolves in the alkaline pore solution; concrete needs zirconia-bearing AR glass fiber.
Is ground glass the same as AR glass fiber?#
No: ground glass is a pozzolan specified by ASTM C1866/C1866M-25 and replaces part of the cement, while AR glass fiber reinforces the mix. The standard (updated 2025-08-01) covers container, plate and E-glass, as set out under ground-glass pozzolan.