Addition of Adfil Fibrin 660F to a conventional ready-mixed concrete at a dosage of 0.9 kg/m³ modifies the plastic-state settlement and bleed-water transport behaviour on slab-on-ground and suspended slab pours. The fiber is a micro-fibrillated polypropylene tape with a nominal cut length of 12 mm, which opens into a network of fibrils under normal compulsory mixing. This network increases the fine-particle surface area within the mortar fraction, reduces the rate of bleed water travelling through capillary channels, and interferes with the coalescence of plastic shrinkage cracks in the first 4–8 h after strike-off. In production, the fiber is added through the plant aggregate weigh hopper or a fibre batching unit after the coarse aggregate and sand are charged, before the cementitious binder and mixing water. The sequence prevents hydrophobic fiber clustering on wet aggregate surfaces. A twin-shaft compulsory mixer with full-speed mixing for at least 60 s after fiber introduction gives acceptable dispersion; truck drum mixing alone after wet batch discharge is not acceptable as the sole dispersion mechanism because aged drum fins and low-speed rotation do not generate sufficient shear to separate the micro-fibrillar bundles. The addition typically lowers slump measured under EN 12350-2 from a control value of 180 mm to 150–160 mm at the same water-cement ratio. When field placing requires the original workability, a polycarboxylate superplasticizer complying with EN 934-2 should be added, rather than increasing batch water because a higher water-cement ratio would compromise cured surface abrasion resistance and increase capillary porosity. In slabs, the function of the micro-fibrillated fiber is not to replace structural reinforcement or to increase post-crack flexural capacity; the fiber is a plastic-state additive for crack-width control and bleed reduction. Evaluation under ASTM C1579-21 on a constrained slab panel can be used to compare plastic shrinkage crack area against an unreinforced control mix; published data for this specific configuration is limited, so project-specific comparative testing is required before a performance specification is fixed. Terminal uses include residential slab-on-grade, multi-storey suspended slab soffits, parking decks, and industrial floor slabs where early finishing and steel trowelling generate surface evaporation rates above 0.5 kg/m²/h and elevate plastic cracking risk. If the relative humidity at the pour site is below 40% or the wind speed above 5 m/s, evaporation control under ACI 305R should remain the primary measure; fiber addition alone does not override inadequate curing. Dosages above 1.8 kg/m³ in conventional ready-mixed concrete can produce visible fiber clumping at the surface after power trowelling, particularly when using high-speed ride-on trowels with pan blades set at aggressive pitch.

What Limits Demoulding Cracking in Thin-Wall Precast Enclosure Panels?

Thin-wall precast concrete enclosure panels with thickness from 70 mm to 120 mm are sensitive to cracking during demoulding, tilting, and transport because the green concrete carries its own mass through a narrow cross-section before full hardening. In such mixes the micro-fibrillated polypropylene fiber is batched at 0.9–1.2 kg/m³ depending on the maximum aggregate size, which is usually 8 mm to 10 mm, and the cement content, which typically ranges from 380 kg/m³ to 420 kg/m³. The fiber is charged into a planetary or turbo compulsory mixer after the dry aggregates and before the first water addition; mixing continues for 90–120 s total. A critical production failure occurs when the high-range water reducer is injected before the fiber has dispersed, because the polymer chains of the superplasticizer and the hydrophobic fiber surface form low-water agglomerates that remain as fibrous nests on the panel face. The panel is compacted on a vibrating table operating at 40–60 Hz for 45–90 s, followed by a surface trowelling pass with a damp steel trowel; the fibrillated network raises green tensile strength sufficiently to reduce edge breakout at demoulding, but it does not function as a macro-synthetic reinforcement for lifting stresses. Compliance for precast elements is defined under EN 13369 common rules for precast concrete products, with the fiber itself covered by EN 14889-2. When severe fire exposure is specified, the fiber dosage may be increased toward 1.5–2.0 kg/m³ because polypropylene melting between 160 °C and 170 °C forms pressure-relief channels during fire-induced spalling; however, this upper dosage must be tested under the relevant fire curve because the mix workability and surface finish are affected. Terminal products include architectural spandrel panels, solid boundary wall panels, transformer enclosure walls, and utility chamber covers. Structural design must still allocate tensile forces to steel reinforcing bars or prestressing strands; the micro-fibrillated fiber does not contribute to characteristic flexural strength under EN 1992-1-1 or ACI 318-19 and is therefore excluded from conventional reinforced-concrete section capacity calculations unless a performance-based test program demonstrates otherwise under EN 14651 or ASTM C1609.

In dry-mix shotcrete production for structural and non-structural concrete repair, Adfil Fibrin 660F is metered into the pre-bagged dry blend at 0.1–0.3% by dry mortar mass, corresponding to roughly 1–3 kg per tonne of repair mortar. The fiber length of 12 mm is selected to remain below the typical nozzle restriction of 25–32 mm and to reduce the occurrence of blockages when sprayed material is conveyed through a rotor/stator spray machine. Dry blending is carried out in a horizontal twin-shaft or ribbon mixer with a fill level not exceeding 70% of gross volume; a mixing time of 3–5 min at low speed is required to distribute the fibrillated fiber without generating the electrostatic charge that separates the micro-fibrils from the mineral fines. High-shear pin mixers should be avoided because the rotating pin tools can wrap the fibrillated bundles into tight nests that survive dry conveying and appear as visible inclusions in the sprayed layers. At the nozzle, compressed air pressure between 0.4 MPa and 0.6 MPa and a nozzle distance of 0.5–1.0 m from the substrate provide acceptable compaction; the fiber tends to reduce early rebound of the coarse fraction, but the rebound reduction is mix-dependent and should be measured on a trial panel before a production specification is fixed. The hardened repair mortar is specified under EN 1504-3 class R3 or R4 for structural and non-structural repair; sprayed concrete quality is evaluated under EN 14488-1 for compressive strength and EN 14488-2 for energy absorption when relevant. The micro-fibrillated fiber is not a substitute for welded wire mesh or macro-synthetic fibers in structural shotcrete linings where post-crack energy absorption is required; for that function a macro-synthetic fiber with a length of 30–60 mm and a diameter above 0.3 mm is normally specified under EN 14889-2 Class II. Terminal uses include hand-applied repair mortars, dry-process shotcrete for tunnel repair, slope protection, swimming pool shell repair, and architectural rockwork where crack control between substrate and overlay is required. The maximum aggregate size should be kept at 10 mm or below to prevent fiber and aggregate interlock in the spray hose; if aggregate larger than 10 mm is unavoidable, the fiber dosage should be moved to the lower end of the range.

When Monolithic Screeds Are Placed Over Underfloor Heating Systems

Cementitious flowing or semi-dry screeds installed over underfloor heating pipes face differential drying shrinkage above the heated pipes, because the local temperature and moisture gradients promote early-age microcracking around the pipe crown. In this application, Adfil Fibrin 660F is dosed at 0.6–1.0 kg/m³ for pump-applied flowing screeds and up to 1.2 kg/m³ for semi-dry screeds that are compacted with a roller screed. The fiber is blended into the dry batch at the silo mixing station before the water content is set to achieve a flow spread of 260–300 mm under EN 12706 for flowing screeds. Because the fiber increases the yield stress of the fine mortar, the same flow class requires a slight increase in polycarboxylate superplasticizer dosage rather than an increase in water; adding water to restore flow would lower the compressive class and increase drying shrinkage, which is counterproductive in heated screeds. The hardened screed is specified under EN 13813:2002 with the designation CT-C30-F5 for flowing cement screeds, where the fiber is considered an additive and not a replacement for the standard mesh or mat reinforcement required by local floor design codes. During the heating cycle after 28 days, the fiber network does not reduce the coefficient of thermal expansion of the cement paste, but it limits the visible crack width that develops where thermal movement is restrained at door thresholds, floor drains, and column penetrations. Field failures observed in pumped screed lines include fiber accumulation at hose couplings when the fiber is added directly to the ready-mixed screed truck without pre-mixing; therefore, the fiber should be introduced through the dry aggregate stream at the batching plant and not into the pump hopper. Terminal floor products include monolithic residential screeds, commercial office raised-floor infill, industrial warehouse overlays, and underfloor heating screeds. The operating boundary for this use is that the fiber does not permit elimination of movement joints prescribed under BS 8204-1 or project specifications based on EN 13813, and crack control at restrained perimeters still depends on joint layout and curing. Overdosing above 1.5 kg/m³ in a flowing screed can produce visible fiber lift on the trowelled surface and should be avoided unless a test panel confirms acceptable surface appearance under the specified power trowel regime.

Gypsum plaster formulations containing the 12 mm micro-fibrillated fiber at 0.05–0.2% by dry mass are used in spray-applied fire protection plasters and manual interior wall renders. The fiber functions differently from its role in cementitious systems because gypsum paste has lower alkalinity and faster setting; the primary benefit is the reduction of surface tearing during the transition from plastic to set state and the improvement of green edge strength at reveals and window returns. The fiber is dry-blended with hemihydrate gypsum and lightweight aggregate in a continuous mixer or low-shear conical screw mixer at a fill level below 65%; using a high-speed disperser above 400 rpm can strip the fibrils from the parent tape and produce a fuzzy, difficult-to-trowel surface. Spray application is performed with a worm-pump plaster machine at air pressure 0.3–0.5 MPa; manual application uses a stainless steel trowel. The fiber addition does not increase the compressive strength of gypsum board cores and is not specified as a reinforcing fiber under EN 13279-1:2008 for gypsum binders and gypsum plasters. Terminal uses include interior plaster finishes, fire-protection plaster around structural steel, and board jointing compounds where a short fibrillated fiber reduces mud-cracking at high water demand. The dosage boundary is 0.3% by dry mass; above this level, trowel drag increases and sanding of the dried surface becomes more difficult. Published data for this specific configuration is limited, so a plant trial with a 1 m² test panel is required before film-thickness specifications are finalised.

Mechanised Production of Segmental Paving and Retaining Block Units

Zero-slump concrete used in segmental paving and retaining block machines requires sufficient green strength to survive immediate demoulding, stacking, and strapping without edge damage. Adfil Fibrin 660F is added at 0.1–0.2% by mass of the dry concrete, approximately 0.9 kg/m³ for a dense zero-slump mix, and is mixed in a paddle mixer for 45–60 s dry before the water and pigment dispersion are introduced. The low water-cement ratio, typically 0.30–0.38, means the fibrillated fiber must be dispersed by aggregate-to-aggregate shear rather than by fluid suspension; therefore, fiber addition to the wet mix after compaction begins is ineffective and leads to surface tufting. The mix is compacted on a vibration press with a frequency range of 50–70 Hz and variable compaction force depending on the block height; the fiber network does not alter the required compaction energy but reduces edge breakout when the product is pushed from the steel mould to the production board. Paving units are specified under EN 1338:2003 for concrete paving blocks, EN 1339:2003 for paving flags, EN 1340:2003 for kerbs, and ASTM C936/C936M-22 for solid concrete interlocking paving units in North America. The fiber does not contribute to flexural strength or freeze-thaw resistance directly; freeze-thaw performance is governed by the air-void system and water absorption limits in the product standard, not by fiber addition. Terminal products include interlocking pavers, permeable paving units, retaining wall blocks, and kerb units. The operational boundary is that the fiber must not be used to reduce the minimum thickness required by product standards, and mix designs with cement contents below 280 kg/m³ may show insufficient paste to bury the fibrillated fiber, leaving visible surface fuzz after weathering.