Different fibre types are used to deliver different performance requirements. Short, thin synthetic fibres are used for fire protection and crack reduction, whilst long synthetic or steel fibres generally come into play to increase energy absorption. One size doesn’t always fit all, and special requirements demand special fibre materials and shapes – Ultra High Performance Concrete (UHPC) requires short fibres with a high E-modulus, for example. Sika provides solutions for all these eventualities, as well as other special types and blends of fibres.
Different fibre types are used to deliver different performance requirements. Short, thin synthetic fibres are used for fire protection and crack reduction, whilst long synthetic or steel fibres generally come into play to increase energy absorption. One size doesn’t always fit all, and special requirements demand special fibre materials and shapes – Ultra High Performance Concrete (UHPC) requires short fibres with a high E-modulus, for example. Sika provides solutions for all these eventualities, as well as other special types and blends of fibres.
Steel Fibres
Steel fibres are characterised by high E-modulus (200 GPa) and high tensile strength (2500 MPa). They prevent creep of the concrete but don’t counteract early-age shrinkage. If any corrosion occurs, it won’t cause spalling of the concrete – just a change of colour on the concrete surface. Protruding steel fibres can pose a risk of injury or damage to waterproofing membranes.
Synthetic Macro-Fibres
Synthetic macro-fibres have a lower E-modulus than steel fibres (5 – 15 GPa). Unlike steel fibres, synthetic macrofibres can’t take extremely high loads, but they’re hugely effective in the early phases of hardening to prevent and / or reduce the size of cracks developing in the concrete. They’re also corrosion-resistant and give the
concrete greater ductility.
Synthetic Micro-Fibres
Synthetic micro-fibres have an even lower E-modulus (3 – 5 GPa) than synthetic macro-fibres. They’re mainly used to reduce early-age shrinkage cracking and to improve fire resistance, thanks to their low melting point (160°C). Like macro-fibres, they’re also corrosion-resistant.
Best use of the different types of fibres
| State of concrete or mortar | Effect / property improvement | Recommended fiber type |
|---|---|---|
| Fresh | Improved rheology | Micro-PP fibres |
| Up to about 12 hours old | Reduction of early-age shrinkage cracking | Micro-PP fibres |
| 1–2 days | Reduction of cracks induced by restraint or temperature | Micro and Macro-PP fibres |
| 28 days’ hardening or more | Transmission of external forces | Macro-PP and Steel fibres |
| 28 days’ hardening or more | Improvement of fire resistance | Micro-PP fibres |