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: how fibre reinforcement works, which fibre types exist, how fibre concrete compares to traditional concrete reinforcement, reinforcement mesh and welded steel mesh, what concrete costs per m3, and how you prevent or repair cracks and concrete degradation.

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. A separate article explains step by step how fibres in concrete bridge cracks, including what changes in the mix and how residual strength is tested.

Fibre types: from steel fibre concrete to synthetic and basalt

Each fibre type has its own profile in terms of strength, workability, cost and application. Steel fibre concrete delivers the highest structural strength at dosages of 25 to 50 kg per m3 and, in many applications — such as industrial floors and foundations — can fully or partly replace traditional reinforcement. Synthetic fibre concrete works with much lower dosages: polypropylene microfibres are exceptionally effective against early shrinkage cracks, while structural synthetic macrofibres replace the reinforcement mesh without being able to rust. Glass and basalt fibres round out this range with high tensile strength and a non-corrosive character that, in the case of basalt, is also heat-resistant and recyclable. For budgeting, the current steel fibre price per kg and the resulting surcharge per m³ at each dosage are set out in a separate article, while synthetic fibre concrete has its own guide to choosing between micro fibres against shrinkage cracks and structural macro fibres that replace mesh.

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.

Comparing, applying and pouring

The central trade-off is between fibre reinforcement and traditional concrete reinforcement — bars, reinforcement mesh or welded steel mesh — and when you choose which. Fibres primarily save time and labour: there is no mesh to weave and set on spacers, 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. If mesh stays in the design, the overview of reinforcement mesh sizes lists the standard sheets and their weights per m², as well as the point at which fibres make the mesh redundant.

After that it becomes practical: how thick should a concrete floor be for each application, what is the right dosage per fibre type, and how does the pour itself proceed — from ordering at the concrete plant and pumping to drying time, curing and aftercare? A monolithic floor or industrial floor makes different demands than a foundation for a shed or garden house. The articles in the Applications and In practice sections each work out these questions, with dosage tables and step-by-step plans. How thick should a concrete floor be? That depends on the use: from the 100 mm minimum for a shed, house or garage floor to 250 mm for a heavily loaded industrial slab. For warehouses and production halls, the guide to reinforced industrial floors compares mesh, steel fibres and synthetic fibres, with floor thickness, dosage and joints per load class.

Costs, damage and repair

Price, too, is a deliberate choice. Costs consist of the base price of concrete per m3 plus a premium for the fibre, but the full picture only emerges once you factor in the labour and lead time saved compared with reinforcement mesh. And if something does go wrong — shrinkage cracks, cracks in a concrete floor or concrete degradation through corrosion of the reinforcing steel — diagnosis is what counts: which cracks are harmful, what does concrete repair cost, and when is prevention with fibres smarter than repair? Current figures are in the price table for fibre reinforced concrete cost, with the price per m³ per strength class and the fibre surcharge per fibre type, and the guide to concrete floor crack repair links each crack type and width to the right repair method, from resin to a fibre reinforced overlay. The articles below each work out these choices in more depth — from the basic mechanism and fibre types to applications, practice, costs, damage repair and the frequently asked questions.