Fibre-reinforced concrete combines the compressive strength of the cementitious matrix with the tensile and flexural load-carrying effect of short fibres distributed throughout the concrete. The material is encountered by experts in building and structural engineering, in tunnelling with fibre-reinforced shotcrete, and increasingly in deconstruction. In practice, the fibre reinforcement affects not only design and execution but also the choice of demolition and separation methods—for example when using concrete pulverizers or hydraulic rock and concrete splitters in the areas of concrete demolition, special demolition as well as building gutting and concrete cutting.
Definition: What is meant by fibre-reinforced concrete
Fibre-reinforced concrete is a concrete that, in addition to the mineral matrix, contains discrete, short fibres. These fibres can be made of steel, glass, basalt, synthetic polymers, or carbon. They are usually randomly oriented and homogeneously distributed in a defined quantity in the fresh concrete. The fibres bridge developing microcracks, limit crack widths, and increase residual load-bearing capacity and energy absorption. Depending on fibre type, geometry, and dosage, targets such as ductility, abrasion resistance, impact toughness, fatigue resistance, or improved crack distribution are achieved. Steel fibre-reinforced concrete (SFRC) is the most widespread form; polymer and glass fibres are often used to limit shrinkage cracking, while carbon fibres are used in high-performance applications.
Composition, fibre types, and dosage
Fibre-reinforced concrete consists of cement paste, aggregates, water, optional admixtures and additions, and the fibre reinforcement. Fibre parameters—material, length, diameter, slenderness, surface, and shape (smooth, profiled, crimped, hooked ends)—govern the bond performance. Typical dosages for steel fibres range from about 20 to 80 kg/m³; for polymer fibres from a few hundred grams to several kilograms per cubic metre. Higher dosages generally improve crack bridging, but can impair workability, pumpability, and surface finishing. For planning it applies: fibre-reinforced concrete does not automatically replace conventional rebar; however, it can partially substitute or complement it for specific verifications. Design is based on the governing codes and project-specific test values of residual flexural tensile strength.
Material properties and mechanisms
The central effect relies on microcrack and crack-bridging mechanisms. Whereas unreinforced concrete loses load-bearing capacity abruptly after cracking, fibre-reinforced concrete provides a residual capacity via the bond between fibre and matrix. This enhances ductility, crack distribution, and fracture energy.
Relevant properties
- Crack control: limitation of crack widths and more uniform crack distribution in service.
- Post-cracking capacity: increased reserves in flexural tension after first crack, important for slabs, industrial floors, and shotcrete.
- Robustness: improved impact and fatigue resistance; reduced notch sensitivity at edges.
- Durability: indirect benefits through controlled crack widths; for steel fibres, corrosion behaviour must be considered, especially at exposed ends.
- Deformation behaviour: higher energy absorption and ductility, relevant in seismically stressed areas or under impact.
Production, mixing technology, and quality assurance
The mixing sequence is crucial to avoid fibre clumping and to achieve uniform dispersion. Fibres are often metered into already homogenized fresh concrete. A plasticizer supports workability; nonetheless, the risk of reduced pumpability must be considered. For shotcrete, coordination with nozzle, delivery line, and water addition is essential.
Practical notes
- Control and document fibre dosage; have batch identification for the fibres available.
- Work samples to check fresh concrete consistency and visual inspection of fibre distribution.
- Supplementary tests to determine residual flexural tensile parameters based on project-specific requirements.
Design and verification
The design of fibre-reinforced concrete is based on characteristic parameters from flexural or pull-out tests. In serviceability, crack width control is paramount; at ultimate limit state, residual flexural tensile capacity governs. Fibre-reinforced concrete is frequently combined with conventional reinforcement, e.g. to ensure tension anchors, punching shear checks, or connection details. In shotcrete for tunnelling, steel fibres can partially replace mesh reinforcement (fabric); assessment is project-specific by the specialist designer.
Applications in concrete demolition and special demolition
In deconstruction, fibre-reinforced concrete behaves differently than unreinforced concrete: fibres hold fragments together longer and bridge separation cracks. This affects strategy and tool selection in the areas of concrete demolition and special demolition as well as building gutting and concrete cutting. Mechanical methods such as concrete pulverizers and hydraulic splitters are often combined with separation and cutting techniques to controllably release fibre-related residual connections.
Selective deconstruction of fibre-reinforced concrete elements
- Preliminary investigation: identification of fibre type and content (e.g. visual inspection, magnet test for steel fibres).
- Pre-cutting: separation cuts to weaken member edges; consider blade wear with steel fibres.
- Segmentation: use of concrete pulverizers for controlled biting and cracking, optionally combined with hydraulic power units for consistent power.
- Breaking: hydraulic splitters or rock wedge splitters generate forced separation cracks; fibre bridges are cut in subsequent steps.
- Finishing: trim protruding steel fibres with steel shears or portable demolition shears; for mixed material packages, hydraulic demolition shears can be advantageous.
Cutting and fragmentation technology
Fibres increase residual cohesion; as a result, processing times per cut or bite increase. Concrete pulverizers benefit from a forward-looking work sequence (initiate cracking – fibre separation – demolition). With hydraulic splitters, crack propagation can be planned; steel fibres counteract crack advance, so pre-drilling and closer splitting spacings can be advantageous. In special applications—for example in confined conditions or sensitive environments—low-vibration methods with low noise emission are in demand, which speaks for hydraulic splitting.
Occupational safety, dust and fibre release
Working on fibre-reinforced concrete generates dust and—depending on fibre type—free fibre ends. General protective measures include effective dust suppression, suitable personal protective equipment, and orderly disposal of fibre residues. With steel fibres, watch out for sharp wire ends and potential “whiplashing” during cutting. Clear segregation of work areas and securing loose fibre bundles reduce risks. Legal requirements on occupational safety and emissions must be checked on a project-specific basis; implementation follows the applicable regulations.
Environment and recycling of fibre-reinforced concrete
Fibre-reinforced concrete can, in principle, be processed into a recycled construction material. For steel fibres, magnetic separation is established; the metal fraction can be returned to the material cycle. Polymer or glass fibres usually remain in the aggregate; RC mixes produced from this can be used in load-bearing or non-load-bearing layers depending on purity and qualification. Source-separated processing through coordinated deconstruction sequences—e.g. initial fragmentation with concrete pulverizers, followed by fine fragmentation and separation—improves the recovery rate.
Typical on-site challenges
- Tool wear: fibres increase wear on cutting edges; plan inspection intervals and have spares available.
- Residual connections: fibre bridges remain after splitting; allow for additional cuts or shearing.
- Surface finishing: steel fibres can stand proud during screeding; choose suitable methods for exposed surfaces.
- Pumpability and sprayability: high fibre dosages require coordinated equipment configuration and mixing sequence.
- Detection in existing structures: fibre-reinforced concrete is not always documented; trial areas and exploratory openings help avoid surprises during deconstruction.
Testing methods and documentation
For planning and quality assurance, tests to determine post-cracking capacity and fibre distribution are common. Flexural tensile tests on specimens provide parameters for design. In deconstruction, material passports, delivery notes, and visual findings support the assessment of the required separation and fragmentation technology. Careful documentation of the chosen methods and waste streams facilitates proof and recycling.
Planning of methods in deconstruction
The choice between cutting, pulverizer operation, and hydraulic splitting depends on member thickness, reinforcement ratio, fibre type, vibration limits, and environmental conditions. In buildings that remain in use, a combination of pre-cuts and low-noise pulverizers is often employed. In rock excavation and tunnel construction, fibre-reinforced shotcrete shells are widespread; there, retention systems, anchoring systems, and layer sequences must be integrated into the deconstruction sequence.
Comparison of fibre types
Steel fibres provide high bond strength and pronounced post-cracking capacity; however, they influence magnetic separation, increase tool wear, and may be visibly corrosive at cut edges. Polymer fibres (macro- and microfibres) are effective against early shrinkage cracking and improve toughness, are corrosion-free, but have lower stiffness. Glass and basalt fibres increase tensile strength and temperature resistance in specific mixes; their suitability depends on alkali resistance. Carbon fibres are used in high-performance applications with very high tensile and fatigue strength; cost and processing requirements are correspondingly higher. Selection is always project-specific and determined by target criteria, durability requirements, and cost-effectiveness.
Fibre-reinforced concrete in tunnelling and shotcrete
In tunnel and underground construction, fibre-reinforced shotcrete is an essential component of temporary and partly permanent supports. Steel fibres ensure even crack distribution and rapid load transfer in early construction stages. For subsequent deconstruction or profile adjustments, planned separation cuts facilitate the use of concrete pulverizers. For profile-accurate demolition with low vibration levels, hydraulic splitting can reduce environmental impact.
Tools and methods for dealing with fibre bridges
Fibre bridges require targeted separation steps. Concrete pulverizers locally split the cross-section; protruding steel fibres are then shortened with steel shears or portable demolition shears. Hydraulic splitters create defined cracks in massive cross-sections; tight drilling patterns and coordinated splitting sequences improve control. Hydraulic power packs provide the energy supply for these tools; constant pressure and flow control support reproducible results. In combination with hydraulic demolition shears, mixed tasks can be handled when, in addition to fibre-reinforced concrete, embedded components and reinforcement steel must be cut.