In mechanised tunnel lining segment production, SikaFiber M12 multifilament polypropylene fibre with a nominal filament length of 12 mm is introduced at a dosage of 0.9–1.5 kg/m³ into a planetary counter-current mixer with a batch volume of 0.75–1.5 m³ after coarse aggregate has been pre-wetted to 0.8–1.2% moisture by mass. The fibre is transferred through a pneumatic lance at 6.0–8.0 bar compressed air for 40–60 s, then mixed at a rotor speed of 12–18 rpm for 90–120 s until a wash-out test shows no clusters exceeding 5 mm. Compliance for the fibre is established under EN 14889-2:2006 and ASTM C1116/C1116M-23 Type III; the precast product falls under EN 13369:2018, with Annex ZA requiring declaration of fibre length, diameter, tensile strength, and alkali resistance. The casting process uses steel-carriage moulds with external vibrators operating at 50–65 Hz, followed by chamber curing at 55–60 °C for 6–8 h until demoulding compressive strengths exceed 15 MPa. The fibre is included to reduce plastic shrinkage cracking on the intrados and to limit microcracking at bolt-pocket corners during demoulding and stacking; it does not replace the steel cage, radial joint bolts, or jacking reinforcement. Terminal product types include universal wedge-jointed rings for TBM-driven metro, rail, and utility tunnels with internal diameters of 5.5–14.0 m. Published data for this exact segment geometry is limited, so pre-production trials should verify fibre distribution through sectioning of full-depth cores at 1.0 m intervals.

What Prevents Early-Age Cracking in Power-Floated Warehouse Slabs at 0.9 kg/m³ Dosage?

Ready-mix plant dosing at 0.6–1.2 kg/m³ is applied for interior slabs where the primary durability objective is control of plastic shrinkage cracking under high evaporation rates, not structural replacement of steel mesh. The fibre is added to the truck mixer after 60–70% of the batch water is in, and the drum is held at 12–16 rpm for 5–7 min; discharge through a 100 mm minimum boom hose reduces clumping at reducer sections. Plastic shrinkage performance is assessed using ASTM C1579-21, with specification limits commonly requiring a crack reduction ratio of at least 40–60% relative to a plain control at an evaporation rate of 1.0 kg/m²/h. Placement by long-strip laser screed with a compaction beam frequency of 3,000–4,500 vibrations per minute is followed by bull floating before bleed water appears, and a curing compound meeting ASTM C309 is applied at 0.2 kg/m² immediately after finishing. Floor flatness tolerances to FF50/FL35 or FM2 remain contractor-controlled and are not improved by the fibre. Governing guidance for joint layout remains ACI 302.1R-15 and The Concrete Society TR34, because the multifilament fibre does not provide the post-crack flexural capacity required to extend sawn joint spacing beyond conventional 4.5–6.0 m grids. Terminal product types include logistics warehouses, freezer slabs, automotive assembly lines, and distribution centres with slab thickness from 150 mm to 225 mm. The operational limitation is that addition above 1.2 kg/m³ in a mix with a slump below 120 mm can increase pump back-pressure and produce visible fibre clumping on power-trowelled surfaces when trowel blade pitch exceeds 15°.

Because wet-mix sprayed concrete is transported through steel pipelines under face pressures of 60–80 bar, polypropylene multifilament fibres are metered into the truck agitator only after the concrete reaches a pumpable slump of 160–200 mm and mixer shear has fallen below a rotor tip speed of 2.5 m/s. The fibre dosage for spoil-heading and service-tunnel linings is 0.9–1.8 kg/m³; mixing continues for 60–90 s at 20–30 rpm before the piston pump is engaged. Nozzle air flow is maintained at 8.0–12.0 m³/min, nozzle distance at 0.8–1.5 m, and accelerator dosage at 4.0–6.0% by mass of binder. Compliance under EN 14487-1:2005 requires the hardened shotcrete fibre content to be verified by washing-out or petrographic counting to EN 14488-7:2006, with a tolerance of ±0.5 kg/m³ against the design dosage. The microreinforcing role is to reduce plastic shrinkage cracking in the fresh lining and to limit surface tearing at tunnel intersections and niches; published data for macro-fibre energy absorption classes to EN 14488-5:2006 is not transferable to this multifilament microfibre configuration. A process conflict occurs when horizontal pumping distance exceeds 200 m or when steel bends below R=0.5 m are introduced: fibre alignment along the flow axis can reduce isotropic crack control and raise rebound to 20–35%. In that condition, the dosage is held at the upper band of 1.8 kg/m³, the line diameter is increased from 50 mm to 65 mm, and the bend radius is reset to 1.0 m minimum. Terminal product types include temporary and permanent sprayed concrete linings in drill-and-blast tunnels, NATM headings, rock slope stabilisation, and protective cladding in mining chambers.

Repair Mortar Placement Through Dry-Process Rotor Machines

On repair sites where pre-bagged polymer-modified repair mortars are conveyed through rotor/stator shotcrete machines, the multifilament fibre is pre-blended at 0.5–1.0 kg/m³ in the dry mortar plant to avoid secondary dosing errors at the nozzle. The rotor machine operates at 2.5–4.0 bar air pressure over a conveying distance of 40–80 m; nozzle water is introduced through a hollow-cone spray to maintain a water/binder ratio of 0.20–0.30. Structural repair products are specified under EN 1504-3:2005 class R4 for load-bearing repairs and class R3 for non-structural repairs; the fibre is declared under EN 14889-2:2006, and the supplier must demonstrate alkali resistance without significant strength loss after immersion in 1 M NaOH at 60 °C for 28 days. Hand-applied trowel mixes avoid forced-action high-shear mixing and use a slow-speed paddle mixer at 200–300 rpm for 90 s, followed by a 5-minute rest and 60 s remix. This sequence prevents fibre tearing and maintains a vertical-repair slump flow of 14–18 cm. Dosage is intentionally limited to 1.0 kg/m³ because higher loadings can reduce chloride diffusion resistance by creating oriented capillary voids at the fibre-matrix interface under vacuum impregnation. Terminal product types include bridge soffit repair, car park spall reinstatement, marine pile collar repair, and historic concrete moulding restoration. Published data for the specific combination of multifilament polypropylene fibre and class R4 shrinkage-compensated mortar is limited; pre-qualification to EN 1504-3 and site trial panels are required before works.

Dry-cast concrete pipe production under packerhead compaction at a fibre addition of 0.9–1.5 kg/m³ relies on immediate demoulding after vertical vibration because the zero-slump mix must retain its cylindrical form without formwork collapse. The multifilament fibre is dry-blended with cement and 0–4 mm coarse sand in a twin-shaft batch mixer for 30 s; water is then added at a water/cement ratio of 0.28–0.34 and mixing continues for 90–120 s until the granulate forms a cohesive crumb. The mix is fed into a packerhead or rollerhead pipe machine with vibration frequency of 65–90 Hz and compaction force of 1.5–2.5 kN/cm of wall perimeter. Compliance is governed by ASTM C76-22 for culvert, storm drain, and sewer pipe, and by EN 1916:2002 for precast concrete pipes with synthetic fibre reinforcement; the fibre dosage must be validated by three-edge bearing tests to the specified D-load class. Fibre addition above 1.5 kg/m³ can absorb free water on the aggregate surface and reduce green strength below 0.3 MPa, causing crown slumping after demoulding. Terminal product types include gravity sewer pipes from DN 300 to DN 3000, storm water culverts, drainage laterals, and pipe jacking segments used in trenchless crossings. The fibre is not a substitute for steel reinforcement cages in high-jacking loads but reduces edge chipping during handling and improves crack-width control during cyclical internal pressure tests.

When Fibre-Reinforced Architectural Precast Panels Are Demoulded at 16 Hours

A 16-hour demoulding window is selected when polypropylene multifilament fibres are added at 0.5–1.2 kg/m³ to facade-grade self-compacting concrete with a binder content of 420–480 kg/m³ and a water/binder ratio of 0.34–0.38. The fibres are dispersed into a twin-screw compulsory mixer before the final third of the superplasticiser is added, avoiding high-torque periods in which screw speed exceeds 30 rpm and fibre entanglement raises apparent yield stress by 20–40 Pa. The mix is poured into tilting-table battery moulds or magnet-clamped steel formwork and consolidated by external vibrators at 55–70 Hz for 20–40 s per station; no internal poker is used because localised shear can orient fibres and produce visible fibre shadowing on the architectural face. The hardening regime uses a two-stage curing schedule: 8–10 h at 40–45 °C followed by 6–8 h at 20 °C before stripping. For precast concrete cladding, the product standard is EN 13369:2018 with the relevant specific cladding standard; the fibre is declared under EN 14889-2:2006. Terminal product types include acid-etched spandrel panels, board-marked facade elements, and lightweight sandwich leafs for unitised curtain wall systems. The operational boundary is that fibre addition above 1.2 kg/m³ in SCC produces a slump-flow drop from 750 mm to below 650 mm unless additional high-range water-reducing admixture is used, and that dosage increase may introduce air voids beyond 2.0% on the cast face.