Fibre reinforced concrete

Fibre reinforced concrete is a collective term for concrete to which steel fibres, synthetic fibres, glass fibres, basalt fibres or combinations of these have been added. These fibres fundamentally change how the concrete behaves once it comes under tensile load. On this page we bring the knowledge together: what fibre reinforcement is, why it works, which choices are involved and which in-depth articles will help you further with your project.

Why fibre reinforcement works

Concrete is strong under compression but weak under tension. Without reinforcement, concrete cracks in a brittle manner: as soon as the tensile strength is exceeded, the load the structure can carry drops off abruptly. Fibres intervene at exactly this moment. They bridge the microcracks that form and carry the tensile forces across the crack — the principle of crack bridging.

The result is that the concrete moves from brittle to ductile behaviour: even after cracking, the structure retains residual strength instead of failing outright. Fibres operate at two scale levels here. Microfibres control the very first, plastic shrinkage cracks in the fresh concrete mix, while macrofibres bridge the larger cracks under load and so contribute to structural strength.

Fibre types and their profile

Each fibre type has its own profile in terms of strength, workability, cost and application. Steel fibres deliver the highest structural strength and wear resistance and, in many applications — such as industrial floors — can fully or partly replace traditional reinforcement. Synthetic fibres (usually polypropylene) are especially effective against early shrinkage cracks and, unlike steel, are not corrosive. Glass and basalt fibres round out this range with high tensile strength and a non-corrosive property that, in the case of basalt, is also heat-resistant and recyclable.

That non-corrosive character is more than a detail. Corrosion of traditional reinforcing steel is one of the main causes of concrete degradation in ageing infrastructure. Where synthetic and basalt fibres are used, that corrosion risk simply does not apply — an advantage that carries particular weight for outdoor and environmentally exposed applications.

Which choices are involved in your project

The central trade-off is between fibre reinforcement and traditional reinforcement — and when you choose which. Fibres primarily save time and labour: there is no reinforcement mesh to weave and place, which delivers the real saving on site. At the same time, fibre reinforcement does not always fully replace traditional reinforcement; for heavy structural work, a reinforcement calculation and sometimes a combination remain necessary.

Dosage, too, is a deliberate choice. It depends on the purpose, the fibre type and the structure, and is ultimately determined jointly by the structural engineer and the supplier. Adding too many fibres is counterproductive, and a homogeneous distribution through the mix is crucial to the result. When having concrete poured, the practical steps follow: ordering the right mix from the concrete plant, preparing the formwork, the pour itself and proper curing.

Finally, there is price. Costs consist of the base price of the concrete plus a premium for the fibre, but the full picture only emerges once you factor in the labour and lead time saved compared with traditional reinforcement mesh. The articles below each work out one of these choices in more depth — from the basic mechanism and fibre types to applications, practice, costs and frequently asked questions.