Adfil Sinta F (SINTA F) is a fibrillated polypropylene fibre supplied as a collated synthetic fibre for cementitious matrices. The product designation identifies the fibrillated film geometry rather than a monofilament, steel-fibre, or macro-synthetic structure. Under high-shear mixing, the collated bundles separate into a branched network of fine polypropylene fibrils that distribute through the fresh concrete. The polymer is a polypropylene homopolymer with a specific gravity reported by the manufacturer in the range of 0.90–0.92 g/cm³. Because the fibre is hydrophobic and resistant to alkaline pore solution, it does not corrode, does not absorb mixing water, and does not participate directly in cement hydration. The primary engineering function of SINTA F is control of plastic shrinkage cracking and plastic settlement cracking in slabs, overlays, precast units, and flatwork. It is not a substitute for structural steel reinforcement, deformed steel fibre, or macro-synthetic fibre intended to provide post-crack residual flexural performance.

Material Constitution and Physical Property Benchmarks

The fibrillated structure is produced by extruding polypropylene film, orienting it longitudinally, and then slitting or embossing to create a lattice of interconnected fibrils. The resulting fibre has a non-circular cross-section and a higher surface area per unit mass than a solid monofilament of equivalent denier. Because fibrillation makes direct diameter measurement ambiguous, specification of this product is best made by cut length, dosage rate, and compliance with ASTM C1116/C1116M-15 Type III synthetic fibre requirements. Manufacturer-published data for SINTA F should be verified against the batch certificate. Representative values for the fibrillated polypropylene fibre class are summarised below.

The cut length most frequently specified for slab-grade applications is 12 mm; alternative lengths may be produced by the manufacturer. Because fibrillation creates a non-circular and branched cross-section, equivalent diameter is not a reliably singular specification parameter. Published data for the exact number of individual fibrils per kilogram is limited, as the splitting ratio depends on mixing energy, aggregate angularity, and batch temperature. The product should therefore be specified by cut length, dosage, and standards compliance rather than by a single diameter value.

The fibre begins to soften near its melting point of 160–170 °C. It should not be exposed to steam-curing regimes above 150 °C because dimensional stability and fibre geometry may be degraded.

In a production-scale twin-shaft mixer of 1.0 m³ batch capacity, the product is introduced into the dry aggregate stream before cement and water. A dry pre-mix interval of 15–20 s allows the aggregate bed to strip the fibrillated bundles apart. At a forced-action pan mixer operating at 30–40 rpm, addition after the first water contact produced visible fibre balls on the paddle arms and reduced distribution uniformity across the discharge gate. The defect was eliminated by returning to dry-blend addition and by resealing opened bags after each withdrawal.

Slump loss measured under ASTM C143/C143M-20 at 0.9 kg/m³ is typically 5–15 mm; at 1.5 kg/m³, the reduction may reach 25 mm in low-slump concrete. A polycarboxylate-based high-range water reducer at 0.2–0.5% by cement weight may be used to restore target slump, but the admixture and fibre should be dosed at separate points in the mixer to avoid destabilising the air-entraining admixture.

Storage of opened bags above 70% relative humidity has been associated with fibre bundling and inconsistent feed behaviour. Bags should be stored flat, off damp floors, and opened at the point of use. If a dry handful does not separate under light mechanical action, the product should not be introduced into the automated batching line.

Fresh-state rheology under ASTM C1749-19 has shown that the relative plastic viscosity of concrete with 0.9 kg/m³ fibrillated polypropylene fibre may increase by 10–30% relative to the same mix without fibre, while the yield stress increase is generally below 10%. The torque response declines as mixing continues and the bundles open; a minimum wet mixing time of 90–120 s after water addition is used in high-shear mixers to reach a stable torque.

What Is the Mechanism of Action in Fresh Cementitious Pastes?

The product functions during the early plastic phase when bleeding, evaporation, and capillary pressure development control crack formation. In the first 8–12 h after placement, water moves upward through the fresh paste. When the evaporation rate at the surface exceeds the bleeding rate, water menisci in the capillary pores generate tensile stress. A plain cementitious matrix cracks when this stress exceeds the still-developing tensile capacity of the fresh paste. The fibrillated network interrupts bleed channels, reduces the continuity of water films around aggregate particles, and bridges incipient shrinkage cracks at multiple points within the same bundle.

Under ASTM C1579-21 restrained plastic shrinkage testing with surface evaporation held at 1.0 kg/m²/h, air temperature at 36 °C, and relative humidity at 30%, published laboratory studies on fibrillated polypropylene fibres of this class report total crack-area reductions of 80–100% at a dosage of 0.9 kg/m³ relative to a plain reference. Published data for the exact SINTA F formulation is limited; project concrete should be verified because cement content, silica fume, aggregate absorption, and admixture chemistry alter both the evaporation rate and the cracking response.

At 0.6 kg/m³ in a slab with water-cement ratio 0.55 and moderate wind exposure, field reports describe reduced but not eliminated early surface cracking. Increasing the dose to 0.9 kg/m³ eliminated visible plastic cracking in the same placement sequence. This dose-dependent response is consistent with the requirement that the fibre count per unit volume be high enough to bridge the active crack population before final set.

Because polypropylene is hydrophobic, the fibre does not corrode and does not undergo alkali-silica reaction. Its effect on the hardened air-void system is not neutral. Under ASTM C231/C231M-24, concrete containing fibrillated polypropylene fibre may show a 0.5–1.5% reduction in measured air content relative to the same mix without fibre, attributed to fibre-induced bubble coalescence during mixing and placement. Where freeze-thaw durability is specified under ASTM C666/C666M-15, the air-entraining admixture dose should be adjusted after fibre addition, and the air-void spacing factor should be checked to ensure it remains below 0.20 mm for critical exposure. The fibre is not a substitute for a correctly entrained air-void system.

In high-strength concrete exposed to fire, polypropylene micro fibres function as a pressure-relief mechanism after melting. The melting point of 160–170 °C is below the temperature associated with explosive spalling in dense low-permeability concrete. At dosages of 1.0–1.5 kg/m³, the fibrillated fibres create temporary channels that allow water vapour to escape under thermal gradients. Published fire test data for this exact product is limited, and the mechanism is documented for the broader class of polypropylene micro fibres under ISO 834-1:1999 and RWS temperature-time curves. Specification for structural fire resistance requires project-specific testing.

In rapid chloride penetration testing under ASTM C1202-22, addition of fibrillated polypropylene fibre at 0.9 kg/m³ has produced variable results depending on paste volume, curing age, and initial charge passed. Published data for this specific configuration is limited. The fibre increases interfacial transition zone volume but does not fundamentally alter the chloride diffusion coefficient of the cementitious matrix; it should not be specified as a chloride barrier.

When a Fibrillated Fibre Is Specified Instead of Steel Mesh or Macro Fibre

SINTA F is considered an alternative to welded wire mesh only for early-age crack control in non-structural slabs, overlays, and similar flatwork. It does not provide structural load capacity after cracking, and it does not satisfy positive moment reinforcement requirements. The distinction is defined by test method. Steel mesh and macro fibres are evaluated by ASTM C1609/C1609M-24 or EN 14651 for residual flexural strength after cracking; fibrillated micro fibres are not designed to deliver measurable post-crack residual strength at the same order of magnitude. In slab-on-ground work where crack-width control is the only requirement and structural flexural capacity is provided by the concrete section itself, the product provides a low-maintenance alternative to mesh that eliminates the risk of mesh misplacement and surface corrosion.

Under ASTM C1116/C1116M-15, both fibrillated and monofilament polypropylene fibres are classified as Type III synthetic fibres. The classification alone does not establish equivalent plastic shrinkage performance. The fibrillated architecture develops a branched mechanical anchor network in the fresh paste, while a solid monofilament relies on longitudinal bond along a smooth perimeter. Comparative selection should therefore be based on cut length, dosage, fibre count, and job-specific ASTM C1579-21 exposure, not solely on Type III designation.

Compared with cellulose fibres, polypropylene does not absorb water and does not degrade in the alkaline cement matrix. Compared with glass fibres, polypropylene is less susceptible to alkaline dissolution in ordinary portland cement, although glass fibre grades designed for cement resistance are outside this comparison. The operational boundary remains the same: SINTA F controls plastic-state cracking and does not provide structural flexural reinforcement.

The product is supplied under a factory production control system aligned with the provisions of EN 14889-2:2006 for polymer fibres for concrete, where applicable. CE marking information, when required, is declared on the packaging or delivery document. The polypropylene raw material is typically assessed for restricted substances under the relevant articles of REACH (EC) No 1907/2006 and, where applicable, RoHS Directive 2011/65/EU. Food-contact approval under FDA 21 CFR is not normally applicable for a concrete reinforcement fibre. Batch certificates should state cut length, specific gravity, and declared dosage tolerance. The purchaser should verify that the received product matches the reference sample because fibrillation geometry may vary with raw material lot and extrusion conditions.

In sprayed concrete and dry-mix application, fibrillated polypropylene fibres of this class are introduced at the dry-mix hopper or in the pre-dampened aggregate stream. The fibre can reduce rebound loss of fines and can control plastic cracking in the fresh sprayed layer, but the addition rate must be limited to avoid hose blockages at restrictive bends. Published data for this exact product in sprayed concrete is limited; spray trials under the intended nozzle configuration are required to establish a workable material flow.

At a pump boom configuration with 50 mm internal diameter hoses and a 90° elbow, adding fibre at 1.0 kg/m³ did not produce a measurable increase in pumping pressure. Increasing the dose to 1.5 kg/m³ produced a higher line pressure and transient blockage at the reducer in one observed placement. This operational limit is equipment-specific and should not be extrapolated without a trial.