Fibra Nycon RSC15-PVA para reforço de concreto (8 denier)

Nycon RSC15-PVA is an 8-denier polyvinyl alcohol monofilament fiber specified for concrete reinforcement. Manufacturer technical literature associates the product with an 8 mm cut length, a nominal specific gravity of 1.30 g/cm³ when measured under ISO 1183-1, a single-filament tensile strength in the range of 1,000 MPa to 1,100 MPa, and a tensile modulus of approximately 33 GPa. Linear density measured under ASTM D1907 or ISO 1973 gives 0.889 g/km; from this value and the specific gravity, the nominal filament diameter is 29.5 μm. The calculated mass per filament at 8 mm cut length is 7.11 × 10⁻⁶ g, so 1 kg contains approximately 1.41 × 10⁸ discrete filaments. This fiber count is the primary engineering variable controlling dispersion, surface area demand, and early-age crack control. Under ASTM C1116/C1116M-23, the material is classified as a Type III synthetic fiber-reinforced concrete component when used as nonstructural secondary reinforcement.

In batching operations, the product is introduced after aggregate and cement but before final water adjustment, with the mixer running at high speed. Because 1 kg of the fiber provides more than 100 m² of filament surface area, the material competes with cement paste for free water. This is a processing conflict rather than a material defect. The lateral surface area per filament is approximately 0.742 mm²; multiplied by the filament count, the total surface area is approximately 105 m²/kg. In low water-to-cementitious ratio mixtures below 0.40, the result is often a measurable slump reduction that must be corrected with high-range water-reducing admixture, not by adding water. Trial batching to ASTM C94/C94M-24 is required to establish the mix adjustment for local cement and aggregate sources.

How Does the 8-Denier Geometry Raise Dispersion Demand in Forced-Action Mixers?

Dispersion difficulty is governed by fiber count and surface area, not solely by fiber mass. At 1.8 kg/m³ dosage, the product contributes approximately 2.54 × 10⁸ filaments per cubic meter. In a forced-action pan mixer or twin-shaft mixer, this population can be distributed uniformly if the fiber is dosed over 30 s to 60 s during wet mixing. In rotating drum mixers, the same dosage frequently produces rope-like clumps at the discharge gate because shear energy is nonuniform. The difference between these equipment types is not addressed by the fiber specification alone; it emerges only in production-scale behavior. Mixer paddle condition is a practical variable: worn paddles reduce shear and produce batch-to-batch variation in fiber distribution even when the batching sequence and dosage remain constant.

The product should be added after initial aggregate and cement mixing, followed by 60 s to 90 s of continued mixing before slump measurement. Slump should be measured under ASTM C143/C143M. If the mixture falls below the specified slump, water addition beyond the approved mix design is not permitted because it changes the water-cementitious ratio and offsets the plastic shrinkage reduction the fiber is intended to provide. Instead, the mix design should be adjusted with a superplasticizer based on trial batching. Published data for this specific configuration across all aggregate sources is limited; therefore, plant trials remain mandatory for repeatable workability retention.

The 29.5 μm filament diameter places the product in the microsynthetic range, but the chemical behavior differs from polyolefin microfibers. PVA is hydrophilic and takes up mix water more readily than polypropylene. At identical water-cementitious ratio, a PVA-dosed mixture may show greater apparent cohesiveness and lower slump. This is not an indicator of poor fiber quality; it is the expected rheological response of high-surface-area hydrophilic filaments. Mixture proportioning should therefore be based on the water demand of the entire system, including fiber surface area, rather than on the original plain concrete mixture.

In slab-on-ground work, nonstructural cracking-control dosages are commonly specified between 0.6 kg/m³ and 1.8 kg/m³. The material is placed by conventional laser-screed or paving equipment without special finishing requirements. Its tensile modulus is close to that of hardened cement paste, but the fiber is not intended to raise structural flexural stiffness. The design function is early-age crack-width control, reduction of plastic settlement, and restraint of bleed-induced surface cracking. Plastic shrinkage performance should be verified under ASTM C1579/C1579M-21, with acceptance criteria for crack area established by the project specification.

For shotcrete, the fiber is batched in dry or wet process mixes and conveyed through the nozzle. Dosages up to 2.6 kg/m³ are used for temporary ground support and slope protection where crack control and rebound reduction are required. Fiber-reinforced shotcrete performance should be qualified by toughness testing under ASTM C1550 or EN 14488-5 when post-peak energy absorption is specified. The 8-denier filament does not provide equivalent toughness to steel macrofibers at the same mass dosage; therefore, substitution is not permissible without project-specific beam or panel testing.

When PVA Is Substituted for Polypropylene in Plastic Shrinkage Control

Substitution of PVA for polypropylene is not a one-to-one mass replacement. Polypropylene monofilament fibers used for plastic shrinkage control generally exhibit tensile strengths between 300 MPa and 600 MPa and elastic moduli between 3 GPa and 8 GPa. The PVA product exhibits tensile strength above 1,000 MPa and modulus near 33 GPa. The critical difference is chemical: PVA contains hydroxyl groups that can form hydrogen bonds with calcium-silicate-hydrate surfaces, whereas polyolefin filaments rely primarily on mechanical anchorage and are hydrophobic. This interfacial bond can produce greater crack-bridging efficiency at small crack openings, but it also increases sensitivity to moisture and mix water demand.

Table entries are compiled from manufacturer technical literature and typical ranges in EN 14889-2:2006 and ASTM C1116/C1116M-23; they do not replace project-specific certification or batch test data. The steel macrofiber range is included because designers sometimes compare PVA with steel fibers at equal mass dosage, which is invalid for structural crack-width control. Steel fibers have higher density and much higher modulus but lower fiber count per kilogram; PVA fibers provide a high number of closely spaced filaments that bridge microcracks but do not produce the same residual flexural strength in cracked concrete.

Because PVA has a specific gravity of 1.30 g/cm³, it remains closer to the density of the fluid cement paste than polypropylene. This reduces buoyancy-driven segregation during vibration and finishing. Polypropylene fibers can migrate to the surface in low-viscosity paste, producing visible fuzz and surface defects under troweled finishes. The PVA product reduces this tendency, but overdosing or insufficient mixing can still produce surface fiber accumulation. Finishing operations should be timed according to the actual bleed rate of the fiber-dosed concrete, not according to the plain concrete baseline.

The 29.5 μm filament diameter and 8 mm length place this product near the upper end of microsynthetic fiber geometry. Compared with finer polypropylene microfibers, it gives lower fiber count at equal mass dosage but higher tensile strength and interfacial bond. Compared with coarser PVA macrofibers, it does not provide the same post-peak crack-bridging capacity. The model designation RSC15-PVA therefore identifies a crack-control fiber rather than a structural macrofiber. Any use in structural residual strength applications requires beam testing under ASTM C1609/C1609M-19a or equivalent project criteria.

Where specification requires formal compliance, the product is evaluated under EN 14889-2:2006 as a polymer microfibre and, in the United States, under ASTM C1116/C1116M-23 Type III. Single-filament tensile strength and elongation are reported using ISO 2062 or ASTM D2256/D2256M. Cut length is verified by ASTM D5103. Batch certificates should record denier, cut length, specific gravity, and tensile strength. For structural applications, the certificate is not sufficient; beam or panel testing on the actual concrete mixture is required because fiber-cement matrix interaction depends on cement chemistry, aggregate angularity, and mixing energy.

Operational Boundaries and Alkaline Stability Limits

The fiber is chemically stable in the alkaline pH range of portland cement concrete, typically pH 12.5–13.5. Prolonged immersion in water can plasticize the filament and change apparent elongation; therefore, mechanical comparisons after mixing should be conducted on hardened concrete rather than on wet-conditioned filaments. Storage should be limited to dry, covered conditions below 60% RH. If bags have been exposed to humid air and clumping is visible, the material should be dried to a moisture content below 0.5% by mass and re-tested for cut length distribution before use.

The product is not intended for autoclave curing above the PVA thermal degradation threshold. Published data for this specific configuration at elevated curing temperatures is limited, and the manufacturer should be consulted for cure regimes above 80°C. In precast elements where cure temperature exceeds normal ambient conditions, trial testing should include flexural and compressive tests on fiber-dosed specimens cured under the actual thermal cycle. This is necessary because PVA may lose strength or undergo dimensional change at extended high-temperature exposure.

The fiber should not be combined with hydrophobic surface coatings or admixtures that may interfere with the hydrogen bonding between PVA and cement hydrates. Compatibility is not covered by routine ASTM concrete testing and requires bench-scale mixing. In production, the most common failure mode is not chemical incompatibility but clumping caused by worn mixer paddles, insufficient wet mixing time, or excessive fiber dosage in low-shear equipment. When fiber clumps appear at discharge from a twin-shaft mixer, the first corrective action is inspection of paddle condition and batching sequence, followed by a reduction in dosage only if the mix design permits.