Fibre Reinforced Facade Encyclopedia: Properties
Tensile strength is the maximum stress a material sustains in direct tension before it fails. In thin facade panels it is rarely the number that governs design, because panels bend rather than pull, but it is the property that explains why fibre reinforcement exists at all. Cement has almost no useful tensile capacity on its own; glass fibre has a great deal. The composite inherits a usable fraction of the fibre, and that fraction is what separates a 12 mm panel that can span between fixings from a piece of mortar that cannot.
A plain cement mortar fails in tension at about 2 to 4 MPa. The alkali resistant glass fibre in it has a tensile strength of well over 1,000 MPa. The composite lands at 5 to 10 MPa, because the strength that reaches the panel is limited by how well the matrix grips the fibre.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Sprayed glass fibre reinforced concrete | 5 to 10 MPa | Typical industry range, 28 day direct tension |
| Premix glass fibre reinforced concrete | 3 to 6 MPa | Lower fibre content and shorter fibres; typical |
| Unreinforced cement mortar | 2 to 4 MPa | For comparison; typical |
| FRP laminate, chopped strand | 70 to 120 MPa | Random in-plane fibre; typical |
| FRP laminate, woven roving | 170 to 270 MPa | Higher fibre volume fraction and continuous fibre; typical |
| AR glass fibre, bare filament | above 1,000 MPa | The fibre, not the composite; typical |
| Glass fibre reinforced gypsum | 4 to 8 MPa | Interior alpha gypsum composites; typical |
| Test methods | ASTM C1275, ASTM D638, ISO 527 | Direct tension coupons; BS EN 1170 covers bending |
| Design basis | Aged and characteristic values with partial factors | Not the 28 day mean |
Why the composite is weaker than its fibre
Tensile strength in a fibre composite is a load transfer problem. The fibre carries the tension, the matrix carries it into the fibre through shear at the interface, and the composite fails when either the fibre breaks or the fibre pulls out. In a well-made laminate with continuous aligned fibre, the fibre breaks and the composite reaches a high fraction of the fibre strength. In a cementitious composite with short randomly oriented fibre, the fibre pulls out long before it breaks, and the composite reaches a small fraction.
Three variables set that fraction. Fibre volume fraction, because more fibre across the crack plane carries more load. Fibre orientation, because a random three-dimensional distribution puts most filaments at an unhelpful angle to the stress. And the quality of the interface, which in a cementitious composite changes over time as the matrix densifies around the filament. The last point is why a design uses aged tensile values rather than 28 day results, exactly as it does for modulus of rupture.
Cementitious composites
Sprayed glass fibre reinforced concrete (GRC, GFRC) reaches roughly 5 to 10 MPa in direct tension, against 20 to 30 MPa in bending. The gap between the two is not a contradiction. In bending, only the outer fibre reaches peak stress and the section redistributes as it cracks, so the calculated flexural stress is higher than the true tensile capacity of the material. That is why modulus of rupture is quoted as the headline figure for panels and direct tensile strength is quoted for analysis.
Polymer composites
Fibre reinforced polymer laminates operate on a different scale entirely. A chopped strand mat laminate reaches roughly 70 to 120 MPa, and a woven roving or multi-axial laminate with a higher fibre volume fraction reaches roughly 170 to 270 MPa. The resin matrix grips the fibre far better than cement does, and the fibre can be placed continuously and oriented deliberately, so far more of the fibre’s capacity reaches the laminate.
This is also why FRP laminates are anisotropic in a way that cementitious composites are not. A unidirectional or woven laminate is strong along the fibre and much weaker across it, so the laminate schedule has to be designed for the load directions in the panel, and test coupons are taken in both directions. ShapeShell-RT is published at 221 to 241 MPa in flexure, which reflects a well-consolidated laminate rather than a chopped strand skin.
The trade-off is stiffness and creep rather than strength. A glass reinforced polymer laminate has a much lower elastic modulus than a cementitious panel of the same thickness, so deflection under wind load and creep under sustained load are usually the governing checks, not tensile capacity.
When tensile strength actually governs
In a facade panel, bending under wind load and self weight governs the field of the panel, and tensile capacity almost never controls the design directly. Where it does matter is local and specific.
- At anchor and fixing points, where load is concentrated into a small area and the panel is pulled, sheared or prised locally
- At corners and returns, where restrained shrinkage and moisture movement generate direct tension across the section
- In a panel restrained against thermal expansion or moisture movement, where the restraint force is a tensile force the panel has to carry
- In stay in place formwork during a pour, where hoop tension develops in a shell full of wet concrete
- In handling and transport, where a panel picked at the wrong points is loaded in ways it was never designed for
Most facade cracking that is not impact damage originates in one of the first three of these. The mitigation is detailing rather than material selection: flexible anchors that allow the panel to move relative to its substructure, joint widths that accommodate movement, and anchor positions chosen so that restraint is not built into the panel.
How it is tested
For production control, most manufacturers test bending rather than tension, because the bending test is quicker, more repeatable and correlates well with the properties that matter. ShapeShell-RC is batch tested for modulus of rupture and limit of proportionality to the GRCA specification. Where a project requires direct tensile data for analysis, it is usually derived from those batch results and from the material’s published aged design values rather than measured panel by panel.
Standards and references
- BS EN 1170 series, Test methods for glass-fibre reinforced cement, including BS EN 1170-4 and 1170-5 bending strength, from which tensile capacity is inferred for design
- ASTM C1275 Standard Test Method for Monotonic Tensile Behavior of Continuous Fiber-Reinforced Composites, where direct tension data is required
- ASTM D638 Standard Test Method for Tensile Properties of Plastics; ISO 527 parts 4 and 5 for fibre reinforced composites
- GRCA Specification for the Manufacture, Curing and Testing of GRC Products, including aged design values
- ASTM C1355 for glass fibre reinforced gypsum composites
- AS 3600 Concrete structures, for the treatment of tensile capacity in cementitious design
Related terms
Questions specifiers ask
What is the tensile strength of GRC?
Roughly 5 to 10 MPa in direct tension for sprayed material and 3 to 6 MPa for premix, against 20 to 30 MPa in bending. The bending figure is higher because only the outer fibre of the section reaches peak stress.
Why is the composite so much weaker than the glass fibre in it?
Because short random fibres in a cement matrix pull out before they break. Only a small fraction of the fibre’s own strength reaches the composite. In a resin laminate with continuous fibre, a much larger fraction does.
Does tensile strength govern facade panel design?
Rarely. Bending under wind load governs the panel field, and stiffness or creep usually governs FRP. Tensile capacity matters locally at anchors, corners and restrained edges.
Why do FRP laminates have such different values?
Because fibre volume fraction and fibre orientation vary enormously between a sprayed chopped strand skin and a woven or multi-axial laminate. The laminate schedule, not the resin, sets the number.
Should design use 28 day values?
No. Cementitious composites change with age as the matrix densifies around the fibre, so design uses aged characteristic values established by accelerated ageing, with partial factors applied.
ShapeShell-RC is batch tested for modulus of rupture and limit of proportionality to the GRCA specification, and test certificates are issued for every project. See ShapeShell-RC specifications
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.