In large-surface ready-mix concrete placements, CHRYSO Fibrin 6mm monofilament polypropylene fibre is typically dosed at 0.6 kg/m³ to 1.8 kg/m³. The 6 mm monofilament engages the capillary pore network during the first 2 h after screeding, when bleeding water evaporation raises pore-water tension beyond the incipient plastic cracking threshold. In slab-on-grade construction, the fibre is discharged onto the aggregate conveyor or into the truck mixer after batching; mixing at 14 rpm to 18 rpm for a minimum of 5 min disperses the individual filaments. The relevant cracking evaluation method is ASTM C1579-21, which uses a restrained panel to quantify plastic shrinkage crack area. Published studies on monofilament polypropylene fibres in cementitious matrices report crack area reduction values commonly between 50% and 70% at 0.9 kg/m³ under ASTM C1579-21 panel exposure; direct transfer to this specific CHRYSO grade requires verification against the manufacturer’s Declaration of Performance under EN 14889-2:2006. The end product is an industrial floor slab or logistics pavement with reduced surface crazing, not an increase in post-crack flexural capacity. Compressive strength measured to EN 12390-3 is generally unchanged at dosages up to 1.5 kg/m³, while slump measured to EN 12350-2 can drop by 10 mm to 20 mm; the mix should be corrected with a high-range water reducer rather than additional water. The fibre does not replace welded wire mesh or dowel baskets, and joint spacing remains governed by geotechnical and slab design assumptions. For exterior slabs with Dmax greater than 20 mm, pre-dispersing the fibre through the aggregate charging sequence prevents filament balling behind mixer discharge gates.

What Changes When 6 mm Monofilament Is Added to Self-Compacting Concrete in Precast Yard Moulds?

In self-compacting concrete for thin-wall precast elements, the 6 mm monofilament is introduced at 0.6 kg/m³ to 1.5 kg/m³ in a high-energy pan mixer with a planetary or turbine rotor. The addition raises plastic viscosity, which must be controlled against the flow criteria of EN 12350-8:2019. A target slump-flow of 650 mm to 750 mm is normally retained if the dosage is kept below 1.5 kg/m³; above this threshold, the V-funnel time may increase to a range where formwork filling slows beyond cycle time targets. Precast facade panels, stay-in-place shutters, and demountable interior partitions are the terminal components. The process conflict in precast production is between high early strength from a low water-cementitious ratio and the need for sufficient mixing energy to separate the monofilaments. A water-cementitious ratio below 0.40 increases yield stress and can trap fibre agglomerates at the mixer wall. Fabrication records from pan mixers show that total mixing time should be extended by 30 s to 60 s compared with the plain SCC reference, but not beyond 180 s total wet mixing, because over-shearing can cause filament breakage and reduce the effective aspect ratio. Demoulding green strength is governed by the concrete matrix rather than the fibre; polypropylene does not participate in hydration. The relevant harmonised product standard is EN 14889-2:2006, and CE marking under Regulation (EU) No 305/2011 requires the fibre to be supplied with a Declaration of Performance stating geometry, tensile strength, modulus of elasticity, and chloride ion content. Published data for the specific CHRYSO Fibrin grade is limited to manufacturer documentation; batch-level conformity should be assessed against the initial type testing results in the DoP.

During silo-blended dry-mix production, the first process bottleneck is not batching accuracy but electrostatic clumping of monofilament fibres on the ploughshare mixer wall. For cementitious screeds and self-smoothing floor toppings, the fibre is typically dry-blended at 0.6 kg/m³ to 1.2 kg/m³ into the sand-cement matrix before the addition of liquid admixtures at the end-user mixing stage. The dry-mix plant uses a low-speed ribbon mixer or a ploughshare mixer at 30 rpm to 40 rpm; blending time from 3 min to 5 min is required to reduce filament balls. The terminal products are 25 kg bagged screed mortars and pumpable floor levelling compounds produced under factory batch control. The performance criterion for the cured screed is cracking risk under restrained drying shrinkage; the relevant product standard is EN 13813:2002, which sets the basic requirements for screed material. Compliance testing for flexural and compressive strength is carried out to EN 13892-2 at 28 d. In unbonded screeds placed over compressible insulation layers with a minimum thickness above 50 mm, the fibre reduces early plastic shrinkage cracking but does not change the design requirements for movement joints, perimeter isolation strips, or nominal reinforcement mesh where specified by national floor design standards. The 6 mm fibre is not a substitute for wire mesh in floating floor constructions, and the elastic modulus of polypropylene is below 5 GPa, so it cannot control long-term structural deflection. Dry-mix producers should verify fibre moisture content by ISO 15512 Method A if storage humidity exceeds 60% RH; polypropylene itself is hydrophobic, but condensation on bagged fibres can introduce clumping that defeats the purpose of pre-blending. Sieve retention on a 2 mm screen after mixing can be used as a batch-release check of dispersion quality.

If Wet-Mix Shotcrete Is Pumped Through a 50 mm Hose at 0.3 m³/h

Adding the 6 mm monofilament to wet-mix shotcrete at 1.0 kg/m³ to 2.0 kg/m³ modifies fresh-state behaviour in two stages. First, in the holding hopper of a piston pump, the fibre increases cohesiveness and reduces bleed segregation before the nozzle. Second, in the nozzle aeration zone, the filaments protrude into the fresh layer and improve early cohesion of the placed material. The relevant spray application standard is EN 14487-1:2005, with sprayed concrete classification by EN 14487-2:2006. The terminal outputs are tunnel lining rehabilitation profiles, rock slope stabilisation, and temporary support shells. The operator must monitor pump line pressure at the rubber hose coupling; a rise of more than 2.5 bar above the plain reference at the same stroke rate indicates insufficient fibre pre-wetting or an excessively dry mix with a water-cement ratio below 0.40. Rebound can be reduced compared with unmodified shotcrete, but published data for this specific configuration is limited to field reports rather than reproducible panel tests. The fibre does not provide long-term flexural toughness in the manner of macro polymer fibres with a length above 30 mm and an equivalent diameter above 0.3 mm. Shotcrete beam tests to EN 14488-3 should be used to determine the residual strength class only if structural ductility is specified; for a 6 mm microfibre, residual flexural strength is typically negligible and should not be entered into design as a load-bearing parameter. Workability at the nozzle should be checked with the slump test to EN 12350-2 before pumping, with a preferred range of 120 mm to 180 mm for piston pumpability. The addition of a high-range water reducer can compensate for the viscosity increase without altering the water-cement ratio.

Repair mortar formulated to EN 1504-3:2006 class R3 or R4 requires a different dosage logic because the aggregate skeleton is finer than 4 mm and the water-cement ratio is often below 0.45. In this matrix, the 6 mm monofilament is added at 0.5 kg/m³ to 1.0 kg/m³, or equivalently 0.25 kg to 0.50 kg per 1000 kg of dry mortar, to intercept plastic shrinkage cracks along patch edges. The restrained shrinkage behaviour is evaluated using ASTM C1581/C1581M-18, where a steel ring imposes circumferential strain on the fresh repair material. The terminal products are concrete repair patches, edge replacement mortars, and thin-section build-up layers on columns and beams. The operational boundary is that polypropylene fibres do not increase the tensile adhesion of the repair mortar to the concrete substrate; adhesion must be tested separately to EN 1542:1999 at the specified minimum value, commonly 2.0 MPa for structural class R4. Adding more than 1.2 kg/m³ in a fine-grained repair mortar can reduce flow below the required application spread and create fibre clustering along trowel strokes. When the repair is applied at thicknesses below 10 mm, the 6 mm fibre can protrude from the surface after trowelling; the surface should be closed with a steel trowel or sponge float before initial set. Curing compounds must be applied per the repair specification; the fibre does not reduce the need for curing at relative humidity above 60% RH.

External Render and Basecoat Crack-Bridging Criteria under EN 13914-2

In external render and basecoat systems, the monofilament fibre is introduced at 0.5 kg/m³ to 1.0 kg/m³ of wet mortar. The mixing sequence in a slow horizontal paddle mixer begins with dry sand and cement, followed by fibre, then water and any air-entraining or water-retaining admixture. The paddle speed is restricted to 20 rpm to 30 rpm to avoid forming fibre ropes on the shaft. The end-products are one-coat render on masonry, basecoats under decorative topcoats, and patch-backing layers over spalled brickwork. The governing application standard is EN 13914-2:2016, which addresses the design, preparation, and application of external rendering. The fibre reduces early plastic shrinkage cracking during the first 24 h after exposure to wind and solar radiation. Water vapour permeability is not materially altered at this dosage; project validation under EN 1015-19:1998 remains required for heritage or insulated retrofit assemblies. Application is constrained by substrate temperature: below 5°C hydration is too slow, and above 30°C surface temperature the mortar skin can dry before the fibre has engaged. The fibre does not replace movement joints in large render panels, and panel distances specified in EN 13914-2:2016 remain mandatory. Do not use the fibre in renders that will receive a pigmented silicone topcoat without confirming alkalinity resistance of the fibre, as polypropylene is stable in cementitious environments but surface topcoat adhesion may be influenced by fibre protrusions.

For precast curbs, drainage channels, and lightweight architectural elements produced by vibration casting, the addition route is often through the charging belt rather than the high-shear mixer. The 6 mm monofilament is dosed at 0.9 kg/m³ to 1.5 kg/m³ and serves primarily to reduce corner spalling and surface cracking during demoulding and yard handling. The elements are governed by EN 1340:2003 for concrete kerbs or by the relevant product standard for the element type. In vibration casting, the fibre can be drawn to the vertical face by high-frequency vibrators operating above 6000 vibrations/min; the compaction time should therefore be limited to the minimum required to close surface voids, and the face mix should be placed before the backing mix. The fibre does not contribute to the characteristic flexural strength declared to EN 12390-5; flexural capacity remains a function of the fine and coarse aggregate packing and the water-cement ratio. Batch-to-batch variance in fibre count per kg should be verified against the supplier’s count certificate because a variation of more than 10% changes the total filament population in a 1 m³ batch by tens of millions of filaments, which affects dispersion quality at the same mixing time. The production yard should store the fibre in closed polyethylene bags below 60% RH and avoid stacking on external racks where condensation can wet the monofilament surface and initiate clumping in the weigh hopper.

Concrete block machine production requires the fibre to be added to the aggregate skip at 0.5 kg/m³ to 1.0 kg/m³. The standard dry blend phase of 60 s before water addition is sufficient.