SINTA 18 mm - Monofilament Polypropylene Micro Fiber is a discrete synthetic filament additive for cementitious mixtures. The material is a single-strand polypropylene monofilament, not a fibrillated tape, supplied at a nominal cut length of 18 mm. In concrete technology it is classified as a Class I polymer micro fibre under EN 14889-2:2006 because the equivalent filament diameter is below 0.30 mm. At a nominal diameter of 18 µm to 30 µm and a polymer density of 0.91 g/cm³, the calculated filament count is approximately 86 million to 240 million filaments per kilogram. Production involves melt-spinning of polypropylene, controlled drawing to orient the polymer chains, and precision cutting to length. Unlike steel fibers, the monofilament is non-corrosive and does not significantly alter the magnetic or electrical conductivity of concrete. Unlike macro-synthetic fibers, the micro fiber is not intended to provide post-crack residual flexural capacity under EN 14651 or ASTM C1609/C1609M; its function is limited to bleed-water control, plastic settlement reduction, and fire-induced spalling permeability.

Which Dimensional and Mechanical Specifications Govern Certification and Batching?

Lot conformity for a polymer micro fibre is assessed under EN 14889-2:2006, with the product designated Class I where the equivalent diameter is less than 0.30 mm. Under the U.S. specification, concrete containing the fibre is classified as Type III synthetic fibre-reinforced concrete under ASTM C1116/C1116M-23. The values in the table are representative of an 18 mm monofilament polypropylene micro fiber; they are not a substitute for the manufacturer certificate of analysis.

The batching system should discharge the fiber within the aggregate weigh hopper or after aggregate transfer. Gravimetric dosing equipment with an accuracy of at least ±0.1 kg is required for dosages at 0.9 kg/m³; volumetric dosing is acceptable only if calibrated against fiber bulk density. Bulk density of chopped monofilament polypropylene can vary from 0.35 g/cm³ to 0.45 g/cm³ depending on packing and filament stiffness, so a loss-in-weight feeder should be calibrated for each bulk bag lot. At 0.9 kg/m³, the water demand is small; however, the high filament count increases total surface area, and slump loss of 10–30 mm has been reported when high-range water reducers are used without dosage adjustment. The product is added before or during initial mixing; extending mixing time beyond 120 s after fiber addition has not shown improved dispersion in published data for similar monofilaments, and may increase fiber breakage.

In high-shear mixing, the separation of monofilaments is governed by mixer speed, drum fill ratio, and filament surface energy. Twin-shaft compulsory mixers with rotor tip speeds of 2.0 m/s to 3.0 m/s distribute an 18 mm monofilament more consistently than gravity mixers, which may require longer dry-mixing intervals of 30–60 s before water addition. Balling in pan mixers is reported when fibers are introduced before aggregate or directly onto a wet batch. A batching sequence that places the fibers on the aggregate belt, between coarse aggregate and cement, reduces clumping because mechanical interlocking of the monofilament with wet fines is postponed. For ready-mixed concrete trucks, adding the bagged fiber directly to the drum at the plant and mixing at 12–18 rpm for 40–60 revolutions is commonly specified; published data for this specific configuration is limited, and a visual washout test of a fresh sample should be performed to confirm individual filament presence. The fiber does not affect setting time under ASTM C403/C403M and does not contribute to air-entrainment instability when dosed with air-entraining admixtures meeting ASTM C260/C260M or EN 934-2, although high dosages can reduce the spacing factor by increasing paste viscosity.

Plastic Shrinkage Crack Control and Fire-Induced Spalling Resistance

The primary use of 18 mm monofilament polypropylene micro fiber is the reduction of plastic shrinkage cracking in concrete slabs, pavements, screeds, and sprayed concrete linings. Under the restrained panel method of ASTM C1579-21, polypropylene micro fibers at 0.6–1.0 kg/m³ have been reported to reduce crack area by 50 % to 85 % relative to plain concrete, with the exact reduction controlled by evaporation rate, concrete depth, and paste volume. The mechanism is not an increase in tensile strength; the fiber network increases the apparent strain capacity of the fresh paste and arrests microcrack propagation by reducing plastic settlement and capillary pressure. Because monofilament polypropylene has an elastic modulus of only 3.5–4.5 GPa, it cannot bridge hardened cracks as steel or macro-synthetic fibers do, and its contribution to post-crack residual strength under EN 14651 or ASTM C1609/C1609M is negligible at dosages below 1.8 kg/m³.

In high-strength or dense concretes, the fiber is used to mitigate explosive spalling under fire exposure. At temperatures between 160 °C and 170 °C, the polypropylene filaments melt and form interconnected channels that increase the permeability of heated concrete. The resulting permeability increase allows water vapor pressure to dissipate; this effect is dosage-dependent and is generally specified at 1.5–3.0 kg/m³ for high-performance concrete exposed to hydrocarbon fire curves such as ISO 834-1:1999. The precise dosage must be determined by furnace testing because excessive polypropylene can increase residual porosity and reduce compressive strength after cooling.

Storage of SINTA 18 mm must avoid direct UV exposure, moisture ingress, and compression damage. Polypropylene is hydrophobic, with water absorption below 0.1 % under ASTM D570-98(2021), but surface moisture can cause filaments to clump or packaging to tear if stored in saturated conditions above 60 % relative humidity. Partially used bags should be resealed and used within the manufacturer-stated shelf life, commonly 24 months from production when stored at 5–40 °C. The product should not be combined with solvent-based curing compounds or aromatic hydrocarbons before mixing, because polypropylene swells in the presence of chlorinated and aromatic solvents. The fiber is chemically stable in the alkaline pore solution of concrete with pH 12–13; it does not hydrolyze like polyester fibers and does not rust like steel fibers. However, polypropylene is vulnerable to strong oxidizing acids, and is not recommended for concrete exposed to continuous high-temperature service above 100 °C, where polymer softening precedes melting and volatile release may occur.

When an 18 mm Monofilament Micro Fiber Replaces Fibrillated Polypropylene or Macro-Synthetic Reinforcement

Selection between monofilament and fibrillated polypropylene micro fibers is determined by dispersion characteristics, exposed-surface finish, and crack-reduction testing under ASTM C1579-21. A monofilament cut to 18 mm has a defined cylindrical cross-section, whereas a fibrillated tape fiber is initially a flat film that splits into interconnected fibrils during mixing. At equal mass dosage, the monofilament typically yields a higher number of discrete filaments per kilogram and a lower visible fiber density on troweled surfaces, but published data for the present product is limited; comparative laboratory trials are recommended. In precast facades and architectural concrete, the monofilament may be preferred because the smaller individual diameter leaves less surface fuzz after acid etching or form stripping. However, fibrillated tapes can provide a larger surface area per fiber mass and may be more efficient in certain mixers if they open fully; if the mixer energy is low, unopened fibrillated fibers can remain as visible tape fragments.

The contrast with macro-synthetic fibers is functional as well as dimensional. Macro fibers at lengths of 40–65 mm and diameters of 0.3–1.0 mm are used at dosages of 3–9 kg/m³ to provide post-crack flexural strength, with residual flexural strength classes defined under EN 14889-2:2006 and test methods in EN 14651 or ASTM C1609/C1609M. The 18 mm polypropylene micro fiber does not replace such macro reinforcement; it is sometimes combined with macro-synthetic or steel fibers when both plastic-shrinkage control and hardened-state ductility are required. The total fiber volume must then account for paste availability, because both fiber classes increase the demand for workability and may require high-range water reducers.

Quality control of SINTA 18 mm on project sites includes verification of bag weight, nominal length, and visual dispersion in fresh concrete. A washout test using a 5 kg sample may be performed on the first mixer, with the water added through a 0.075 mm sieve to retain fibers. The recovered mass should be compared with the expected fiber mass for the sampled volume; deviations greater than ±5 % require an inspection of the dosing gate and mixing speed. Mechanical property tests are generally not required for microfibers at low dosage. Acceptance should reference the manufacturer certificate, EN 14889-2:2006 CE marking where applicable, and the project specification. When the product is used for fire spalling mitigation, a furnace test of the exact mix design should be carried out before production because cement type, aggregate moisture, and silica fume content alter the required dosage. No additional curing temperature or maturity restrictions apply beyond those for the base concrete, but the use of polypropylene fiber does not reduce the minimum curing period specified by ACI 308 or EN 13670.